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4.ARC WELDING PRO-CESSES

In arc welding, the joint betweenthe pieces to be assembled ismade by filling an appropriateshape (Vee, cross, bell) with a fillermetal (rod or wire) which is meltedstep by step. The joint can be filledin one or more passes. As the fillermetal melts, so do the edges ofthe components that are beingjoined together (unlike in brazing).

Ever since the arc welding ofaluminium in inert gases (argon orhelium) came into widespreadindustrial use, there have alwaysbeen two main processes but theytend to complement rather thancompete with one another (table48, p. 97). One, TIG, is mainlymanual, while the other, MIG, canbe fully automated. MIG weldinghas advanced in great stridessince the early Nineties to thepoint where the conditions underwhich aluminium is welded arenow greatly enhanced.

The mechanical properties of theweld seams are identical in bothprocesses, all other things beingequal, i.e. parent alloy, filler metaland material thickness.

4.1TIG welding(Tungsten Inert Gas)

In TIG welding (16), the electric arcforms between a refractorytungsten electrode and the pieceto be welded. The shielding gas –usually argon – is blown outthrough the nozzle of the torch(figure 77).

In manual TIG welding, the fillermetal in the form of a straightenedwire rod (0.8 mm to 4.0 mm indiameter) is held manually by thewelder. In automated TIG welding,the filler metal is fed automatically

from a reel of wire of diameter 0.8mm to 2.0 mm by a motoriseddispenser.

Welding machines operate withstabilised HF alternating currentfor manual welding or continuousor pulsed d.c. current forautomatic welding. Machinesmust be fitted with an electroniccircuit board designed foraluminium welding, with a pulsearc stabiliser and an arc re-igniter.

The geometry of the refractoryelectrodes is an important factorinfluencing the quality of the weld.The electrode must be groundsharp unless the welding machineruns on a.c. current. For d.c.current, the electrode tip must beinside a cone of 30 to 60 degrees,and machining (or grinding) marksmust run parallel to thelongitudinal axis of the electrode(figure 78).

6. WELDING

93

PRINCIPLE OF TIG WELDING

Welding torchCurrent input

Argon gas inletWater return

Shielding gasGaseous atmosphere

Solidified metal

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Direction of welding

Nozzle

Filler metalBase metal

Tungstenelectrode

Coolingwater inlet

GRINDING OF TIG ELECTRODESGOOD BAD BAD

Correctelectrode Currenttoo high Contaminatedelectrode

30 à 60°

TIG continuousA.C.TIG

Figure 78

Figure 77

(16) The process is known as WIG inGermany (tungsten in German is‘Wolfram’) and GTAW in America (GasTungsten Arc Welding).

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TIG uses less power than MIG, sothe heat affected zone is wider(because of the diffusioncoefficient) and there is moredistortion due to expansion. Therate of welding which is controlledby the welder is relatively slow, inthe region of 0.2 m.min-1.

TIG welding is above all a manualprocess and simple to use,allowing meticulous workmanshipand precision results. Welding ispossible in all positions. It issuitable for material 1 to 6 mmthick. It can be used to weld withclearances that are over twice thethickness of components under1.5 mm thick.

TIG is difficult to automate so islimited to use in the developmentof prototypes and in the repair ofdefective welds.

4.2MIG welding (Metal Inert Gas)

In MIG welding (17), the filler wirealso acts as the electrodesupplying the power (figure 79).The wire is automatically uncoiledfrom a reel and fed to the weldingtool (gun or torch) as it is used up.

The welding power is proportionalto the amount of wire that is fed tothe weld seam, and is supplied bya d.c. power source which can becontinuous or pulsed. Connectionis made with reverse polarity, i.e.the workpiece is alwaysconnected to the minus (negative)pole to ensure descaling of theoxide film.

MIG welding is ‘self-pickling’because the transfer of electronsfrom the workpiece to the fillerwire breaks the oxide film(provided it is very thin, severalnanometers).

A thick oxide layer that has formedfollowing long exposure toambient humidity cannot be fully

removed, and the weld seam willhave oxide inclusions (defect 303,cf table 54, p. 104). Semi-finishedproducts should therefore bestored under cover in a dry place(18).

The welding current varies from40 to 700 Amps depending on anumber of parameters such as thediameter of the filler wire, theposition of the weld, the size ofthe components etc.

The classic MIG process usingcontinuous current has manyadvantages: ■ excellent productivity due to thehigh rate of filler metal deposition,■ good penetration, ■ low splatter, ■ the process can be automated.

4.3Synergic pulsed MIG

MIG welding has made greatadvances since the appearance inthe early Eighties of so-called“synergic pulsed current” genera-tors in which the current is sup-plied by power transistors.

Prior to this, power was suppliedby thyristor generators whosepulse frequency was a direct func-tion of the mains frequency.Settings were difficult and lackedflexibility because the speed ofthe wire had to be adjustedaccording to the frequency.

Synergic pulsed current genera-tors allow the welding cycle to beregulated (figure 80) to give:■ high current at the start of theweld to avoid lack of fusion andpenetration, and■ low current at the end of theweld to prevent crater formation.

94

PRINCIPLE OF MIG WELDING

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Welding torch

Nozzle

Contact tube

Electrode wireGaseous atmosphere

Base metalSolidified metal

Molten metalElectric arc

Shielding gas

Positive polarity(+) at the electrode

Figure 79

(17) Still also known as MAG (MetalActive Gas) or GMAW (Gas Metal ArcWelding). (18) Cf. Section 5.

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6. WELDING

The welder can control threeparameters to optimise the weldseam:■ the speed of the wire, propor-tional to the welding current,■ the welding speed,■ the height of the arc, proportio-nal to the welding voltage.

With these machines, theparameters adjust automatically tothe displayed speed of the wire.Settings can be refined byadjusting the height of the arc.

In this system, the metal istransferred “drop by drop” (i.e.

one drop of metal per pulse),allowing the minimum weldablethickness to be reduced from 3 toaround 1 mm (19).

Pulsed MIG offers a number ofadditional benefits overconventional MIG welding withcontinuous current:■ welds can be made in any posi-tion,■ distortion is limited (low powerinput),■ limited weld repairs and fewer innumber,■ wide range of thicknesses withthe same diameter wire,

■ good joint quality and goodmechanical properties,■ good appearance of the weldseam, especially with spraytransfer,■ process can be fully automated.

95

SYNERGIC WELDING CYCLE

> 700 Aoverco-mes the aluminalayerWelding current Striking ls peak

Start-up current (hot start) Welding current Crater filler

currenttime

Good penetrationfrom the start(avoids incipientfracture)

No craters at theend of the bead(avoid cracking)

From Air Liquide WeldingFigure 80

(19) With the old-type generators thetransfer of metal by spraying was onlypossible at 20 V and over. Below thisvoltage, globule or short-circuit transferis unsuited to the welding of aluminium,which accounts for the minimumthickness of 3 mm.

Time

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4.4“Spray MODAL”synergic MIG withmodulated current

There is now a variant of thesynergic welding technique – the“Spray Modal” process (20). Itoperates with modulated currentwhich falls very rapidly over a veryshort period of time (severalmilliseconds) with every pulseduring which several drops of fillerare projected into the weld pool(figure 81). These rapid variationsin voltage within the arc cause theweld pool to vibrate, encouragingthe evacuation of hydrogenbubbles from the metal while it isstill liquid.

Compared with synergic pulsedMIG, Spray-MODAL welding ■ reduces or even eliminatesporosity in the weld (figure 82).■ enhances penetration,■ increases welding speed..

4.5Filler wires

An evenly dispensed filler wire willensure good arc stability andhence the quality of the weld.The low rigidity of the filler wiresrequires the use of suitable

dispensers to minimise thechances of the wire snagging inthe torch tube which must bemade of PTFE (“Teflon”) toeliminate risks of abrasion.

A torch with a push/pull wiredispensing system isrecommended to ensure optimumdispensing regularity, especiallywhen using the 4043A wire gradeand in automated welding.

Filler wire is usually 1.2 mm indiameter, although there are also1.6 mm gauge wires; these aremore rigid and their use is growingwith pulse MIG. They are alsoused when the rate of depositionis high.

Shaving the filler wires in the finaldrawing pass has a number ofeffects, all of which enhance thequality of the weld:

■ it eliminates the outer zonewhich can be the site of magne-sium segregation,■ it removes traces of grease,■ it ‘sizes’ the weld which removessurface irregularities that are areasof moisture retention (figure 83).

96

THE SPRAY-MODAL PROCESS

MIG PULSED CURRENT

➤

➤Frequency

➤

➤

➤

➤

Background current

Pulse voltage

MIG SPRAY MODAL - SAFFrequency

Spray current

➤

➤

Weldingvoltage

➤

➤

Background current

➤

➤

MIG pulsed current Spray MODALTM

Average current

±10 drops perpulse1 drop perpulse

Figure 81

EFFECT OF SPRAY-MODAL ON POROSITY

Spray Arc

Spray MODALTMPoros

ity su

rface

(mm2 )

for a

100 m

m we

ld be

ad

Wire speed in cm/min

25

20

15

10

5

0 25 30 35 40 45

Welding conditions :• part : part in 5456A - thickness 10 mm• wire : wire in 5356 - diameter 1,2 mm• H2 : 2000 ppm• I : 216 A• U : 23 V• wire speed : 12,5 m/min

From Air liquide WeldingFigure 82

GX50From Air liquide Welding

SURFACE CONDITIONOF FILLER WIRES

Figure 83

(20) Patented by Air Liquide.

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6. WELDING

5.STORAGE OF SEMI-FINISHEDPRODUCTS AND FILLER WIRE

Given aluminium’s very strongaffinity for hydrogen when in theliquid state (figure 60, p. 86), it isessential to remove all possiblesources of that element, especiallymoisture which can deposit onsemis and filler wire in storage andhydrate the oxide layer.

Filler wire is always supplied insealed packs that must be storedin an enclosed, covered roomthat is at the same temperatureas the welding shop. The packsshould not be opened untilrequired for use.

When welding operations arecomplete, any wire left on the reelmust be stored in a cabinetmaintained at a constant 40 °C. 97

PARAMETERS OF TIG AND MIGWELDING

Thickness 1 mm andover, in several passes ifnecessaryAll welded fabrications

Thickness 1 to 6 mmPrototypesRepairing defective welds

Thickness 0.1 to 10 mmAutomated welding withgood weld quality

Application

Faster: 0.40 to 1 m/min-1Slow: 0.15 to 0.30 m/min-10.30 to 0.60 m/min-1Welding speed

Argon or a mixture of 30%argon, 70% helium (*, **) Flow 1 l/min-1 for a nozzle18 to 25 mm in diameter

Argon or mixture of 70%argon, 30% helium(*) Flow 10 l/min-1

HeliumGas

80° in the direction ofmotion

80° in the direction ofadvance

80° in the direction ofadvance

Torch angle

Filler wirePure tungstenZirconium tungstenElectrodes

Direct, with very shallowtrailing edge. A pulsedsource is a good option forslender work.

Alternating with HF andarc decay (speciallydesigned for aluminiumalloys).

DirectCurrent source

d.c. MIGa.c. TIGd.c. TIG

(*) The helium in argon/helium mixtures increases the welding speed and improves penetration. Table 48(**) Pulse MIG and Spray MODAL™ synergic MIG methods operate mainly with argon.

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6.SURFACEPREPARATION

Other sources of hydrogen are therolling and forming greases andoils left on the surface of themetal, and other impurities of dif-ferent types, such as traces ofpaint.

The surface of the metal musttherefore be cleaned very carefullyon both sides, starting by degreas-ing with a non-chlorinated solventto dissolve the greases and oils(21). Solvents are themselveshydrocarbon compounds contain-ing hydrogen atoms, so great caremust be taken to ensure no traceis left prior to welding.

After degreasing, the edges mustbe brushed (after chamfering asnecessary) on both sides of themetal and over a sufficient widththat is at least equal to the widthof the heat affected zone, i.e. 25mm. A rotary brush with stainlesssteel wires should be used forthis.

Whatever method of brushing isused (manual or mechanical) thebrush itself must be very cleanand operators must wear gloves.

The “life” of surface preparation iscertainly no more than one day,after which time the oxide filmmay well absorb moisture oncemore, especially in humid environ-ments (22).

To eliminate moisture, just prior towelding an oxy-acetylene torchcan be used to pre-heat the edgesat a temperature above dew pointin the region of 30 to 40 °C.

7.JOINT PREPARA-TIONAND SETUP

These operations are veryimportant, and will determine thequality of the weld and its fatigueresistance. For example,excessive clearance between theworkpieces can cause the weldseam to collapse and lead to theformation of undercuts that can bevery detrimental to the quality ofthe weld and its fatigueresistance.

The type of edge preparation willdepend on: ■ the thickness of the work,■ the type of weld: butt, flat or fillet,vertical, overhead or horizontal,■ the use of a liner, whether per-manent or not.

As a general rule, the edges ofmaterial up to 4 mm thick are notchamfered.

Ideally, edges that are to bewelded should be prepared bymachining with a coarse-toothcutter or if this is not available,manually using a coarse file. Avoidgrinding with corundum or resinwheels.

Workpiece configuration is alsoimportant; this relates to:■ the clearance between theworkpieces – this must be assmall as possible (23) to preventdistortion,■ the size and shape of the liner(stainless steel).

Tables 49 and 50 illustrate anumber of examples of edgepreparation and configurationfound in shipbuilding.

8.FILLER METAL

The filler metal must becompatible with the chemicalcomposition of the parent alloysthat are to be welded, and mustensure the best possibleweldability.

The choice will also depend on themechanical properties andcorrosion resistance that the jointis required to have.

For the aluminium alloys that areused in shipbuilding (and othermarine applications), the fillermetals are:■ silicon alloys, mainly 4043A,4045, 4047A,■ magnesium alloys, mainly 5356,5183, 5556A.Their compositions are shown intable 51, p. 100.

Table 52, p. 101 - taken from EN1011–4 (24) - shows possiblechoices of filler metal according tothe hierarchy of criteria used forthe weld. 5183 is the best fillermetal for welding Sealium®.

98

(21) Chemical pickling in alkaline bathsshould be avoided at all cost. Thoroughwashing is essential and experienceshows that this is often inadequate, witha risk of subsequent corrosion by tracesof the alkaline medium.(22) BS 8118 “Structural use ofaluminium, Part 2 Specification formaterials, workmanship and protection”states that the time between cleaningand welding must not exceed 6 hours.(23) Zero clearance is the ideal. (24) Standard EN 1011-4. Welding –Recommendations for welding ofmetallic materials. Part 4: Arc welding ofaluminium and aluminium alloys.

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6. WELDING

99

EXAMPLES OF EDGE PREPARATION FOR BUTT WELDING MIG WELDING

α = 70/90° for flatand overheadweldsα = 70° for verticalwelds

t > 10none2 sidesalternately

Flat,vertical,overhead

Material over 12 mmthick should be weldedautomatically with ahigh current (+).Improvement andvisibility of the weld

8 < t < 30none2 sidesalternately

Flat

Max. gap 2 mmtemporary

Max. gap 1.5 mm Back-weld advisablefor h = 3 mm (*)

3 < t < 25none1 side only Flat,vertical,overhead

t1 = t + 1 mm with max. 6 mm

permanent

Max. gap 3 mmtemporary

Max. gap 1.5 mm Back-weld advisablefor t > 4 mm (*)

3 < t ≤ 6none1 side onlyAll

RemarksPreparationThickness(mm)LinerWeldingPosition

(*) Where a back-weld is advisable, it must be welded after gouging to the base of the first pass. Table 49(*) Taken from standard NF 87-010 "Aluminium et alliages d'aluminium – Soudage – Préparation des bords" (Aluminium and aluminium alloys – Welding – Edge preparation).

➤

➤

➤

➤t

t 1

t

Weld or track

➤

➤

➤

➤

➤

➤

➤

➤

➤

➤

➤

➤

➤

➤

➤

Gaph h 1

t

70°

➤

➤

➤➤

➤ ➤

Gap

0,5mm

For visibility if required 0,5mm

➤

➤70°

Gap ➤

➤

➤

➤

➤

➤ht

➤

➤

➤

➤➤

➤

t

(Broken corners)(+)

1mm

1mm

➤

➤α

➤

➤➤

➤t

1,5to

3mm

➤

➤

t

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9.FINISHING

The purpose of weld finishingoperations is to:■ repair defective weldments,■ remove any black deposits leftby welding,■ correct structures with exces-sive distortion,

■ shave the seam,■ put the seam in compression byshot-peening,■ complete the concavity of theseam.

100

EXAMPLES OF EDGE PREPARATION FOR FILLET WELDS MIG WELDING (WELDS IN ALL POSITIONS, NO LINER)

α = 70 °. Back-weld if possiblet > 61 side

If possible 1 back pass on otherside, 5 mm groove (*)

t > 41 side

t > 42 sides alternatelyor simultaneously,automatic flatwelding

RemarksPreparationThickness(mm)Welding

(*) Where a back-weld is advisable, it must be welded after gouging to the base of the first pass. Table 50(*) Taken from standard NF 87-010 "Aluminium et alliages d'aluminium – Soudage – Préparation des bords" (Aluminium and aluminium alloys – Welding – Edge preparation).

➤

➤

➤

➤

2mm

➤ Max.

gap

t➤

➤

➤

➤

1,5mm

➤

➤

Max.

gap

➤

➤

3mmt

60°

➤

➤➤

➤

➤

➤

➤tht

h=t/4 to t/3

➤

➤α

CHEMICAL COMPOSITION OF FILLER METALS (*)Alloy Si Fe Cu Mn Mg Cr Zn Ti4043A 4,5 0,6 0,30 0,15 0,20 0,10 0,15

6,04045 9,0 0,5 0,30 0,03 0,05 0,10 0,20

11,04047A 11,0 0,6 0,30 0,15 0,10 0,20 0,15

13,05356 0,25 0,40 0,10 0,05 4,5 0,05 0,10 0,06

0,20 5,5 0,20 0,205183 0,40 0,40 0,10 0,50 4,3 0,05 0,25 0,15

1,0 5,2 0,255556A 0,25 0,40 0,10 0,6 5,0 0,05 0,20 0,05

1,0 5,5 0,20 0,205556 (**) 0,25 0,40 0,10 0,50 4,7 0,05 0,25 0,05

1,0 5,5 0,20 0,20(*) According to standard EN 573-3, Part 3: Aluminium and aluminium alloys – Chemical composition, except for the 5556. Table 51(**) According to the Aluminum Association.

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9.1Repair of defectivewelds

If inspection (X-ray, ultrasonic etc.)reveals unacceptable weldimperfections then the weld mustbe repaired.

On material under 4 mm thick,defective areas can be removedwith a rotary tungsten carbidecutter mounted in a pneumatic

drill. The axis of rotation of thecutter must be parallel to the axisof the weld so as to avoid incipientcracks.

For material over 4 mm thick, thedefective areas should beremoved with a pneumatichammer fitted with a gouge (25).

The weld is then repaired by thesame process (TIG or MIG) as wasused to make the initial joint.

Minor imperfections are nearlyalways repaired by TIG weldinghowever, thickness allowing.

6. WELDING

101

Each combination has three possible choices - indicated where the lines intersect - depending on the selected criterion: Optimum mechanical properties: top line – Optimum resistance to corrosion: middle line – Optimum weldability:bottom lineThe filler metal indicated is: 4 : series 4xxx → 4043A, 4045, 4047A – 5 : series 5xxx → 5356, 5183, 5556A

Alloy A

Wrought 55000 Series 5 (a)Mg < 3 % 4 - 5 (b)Wrought 5 5

5000 Series 5 5Mg > 3 % (a) 5 5

Wrought 5 - 4 5 - 4 5 - 46000 Series 5 5 5

4 4 4Wrought 5 - 4 5 - 4 5 - 4 5 - 4

7000 Series 5 5 5without copper 4 4 4

Cast 4 (e) 5 - 4 (e) 4 4 4 (d)Si > 7 % 4 5 4 4

(c) 4 4 4 4Wrought Wrought Wrought Wrought Cast

Alloy B 5000 Series 5000 Series 6000 Series 7000 Series Si > 7 %Mg < 3 % Mg > 3 % without copper (c)

(a) 5000 series alloys with more than 3.5 % Mg are sensitive to intergranular corrosion Table 52when exposed to temperatures over 65°C and when used in certain aggressive environments (26).(b) 5000 series alloys with less than 3 % Mg and 3000 series alloys that contain magnesium may be sensitive to hot cracking.(c) The mechanical performance of the weld depends on the internal soundness of the castings. Gassed materials and injection mouldings are considered to be non-weldable.(d) The percentage of silicon in the filler wire must be as near as possible to that in the casting.(e) The welding of aluminium-silicon castings (40000 series) to 5000 series alloys should be avoided where possible as Mg2Si intermetallics form in the weldment and weaken the joint.

(25) Carbon arc gouging is not advisableas it may introduce carbon into the weldseam.(26) Cf. Chapter 10, Section 10-2.

CHOICE OF FILLER METALS AS A FUNCTION OF THE ALLOY COMBINATION

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9.2Cleaning

Very fine black deposits of “soot”can often be seen sticking to thesurface of the metal at the edge ofthe weld seam after MIG welding,especially when 5000 seriessemis are welded with 5356 alloyas the filler metal.

4043A filler wire leaves nodeposits (except possibly at thestart and finish of the weld) pro-vided the welding equipment isset correctly.

This “soot” consists of particles ofoxides (of aluminium and magne-sium) caused by small amounts offiller metal vaporising in the arc,

the temperature of the arc beinghigher than the boiling point of alu-minium and magnesium. Thevapour immediately condenses oncold parts of the sheet near to theweld.

These deposits only affect theappearance of the weld and haveno impact on its mechanical prop-erties or corrosion resistance.

This “soot” can be brushed off witha metal brush. This should be doneas soon as possible after weldingas it becomes much more difficultto remove if left for several hours.

9.3Correcting distortion

Minor distortion in sheet under 3mm thick can be corrected with ahammer or mallet.

When sheets are bulged (figure84), the welding torch can beused to apply “shrinkage heat” aslocally as possible to the bulges.The heat makes these con-strained areas expand (thewelded zones are shorter thanthe sheet), and they are com-pressed. Rapid cooling – with ajet of water if necessary – thencauses shrinkage which placesthe piece under stress and so cor-rects the warp. “Shrinkage heat”may also be combined with ham-mering.

It is trickier to apply “shrinkageheat “ to aluminium than to steelbecause of the high diffusion ofheat. Unlike steel, aluminium doesnot change colour so the tempera-ture must be checked with tallowor thermocolour pencils.

Shrinkage heat does not affect themechanical properties of 5000alloys in the O or H111 condition.However it anneals 6000 seriesalloys and so reduces theirmechanical properties.

9.4Shaving

Shaving the weld seam very sig-nificantly improves the fatigueresistance of the joint provided theseam is free from internal flawswhich shaving would expose.

According to BS 8118 for example,shaving increases the endurancelimit of a seam from 24 MPa for a120° angle to 50 MPa for a shavedseam (27).

Welds are normally shaved with afine abrasive wheel (50 to 80 grit).

9.5Shot-peening

Shot-peening a weld seam puts itssurface in compression, neutralis-ing internal stresses detrimentalto the weldment’s fatiguestrength.

Different types of shot can beused – glass, ceramic or steel –but it is the latter two which signif-icantly enhance fatigue strength(figure 85).

Although there is no way of verify-ing the efficiency of these treat-ments, they can be applied to thewelds of “hot spots”.

102102

DISTORTION OF PARTS IN COMPRESSION

Dishing

➤

➤

EFFECT OF PRE-STRESS SHOTPEENING

As weldedGlassshot

CeramicshotSteelshot

Failure Failure NofailureNofailure

107

106

105

104

103

Fatig

ue st

rength

at 90

MPa

, R =

0,1

5086 H111, 6 mm MIG butt weldsFigure 85

Figure 84

(27) Cf. figure 45, p. 65.

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6. WELDING

103

10.INSPECTION

The purpose of inspection is toevaluate the quality of fabricatedproducts and more specifically tograde the quality of a weld againstan acceptable level of defects.

The acceptable level of defects isdetermined by a number ofparameters:

■ the load modes and load condi-tions – static and dynamic, ■ the levels and variations ofstress,■ the safety of persons and pro-perty,■ the technical and financialconsequences of failure,■ the options for routine operatio-nal inspection and control.

10.1Approval procedures

Approval procedures are contrac-tual but they also make referenceto standards (if any) and to the reg-ulations of classification societies,especially as regards the qualifica-tion of welders.

They may be complemented bythe fabricator’s own inhouse pro-cedures, governing welding meth-ods in particular.

Tensile and bending tests are con-ducted on test specimens follow-ing approval procedures laid downby the classification societies.These tests are very important asthey can help:■ to detect a lack of fusion that ishard to identify by NDT testing,and■ to adjust parameters so as tolimit defects.

10.2Testing welded joints

The frequency and extent of weldtesting will depend on a number ofcriteria, such as: ■ structure, ■ rate of stress, ■ any loads imposed on thewelds.

In the course of fabrication it ispossible to perform: ■ non-destructive tests includingrandom X-ray testing (28), ultraso-nic etc.,■ visual inspection and dye-pene-tration (29) which can be perfor-med over the whole of somewelds to detect incipient cracks,■ tests of mechanical propertiesand bending tests on specimenstaken from batches of weldedmetal according to the currentmethods

11.WELD IMPERFEC-TIONS

The causes of weld imperfectionsare numerous, and are a result ofeither the preparation of the metalor poor workmanship.

The most common defectsencountered in aluminium weldingare virtually the same as are foundin the welding of steel: isolatedcracks (‘star cracks’) or longitudinalcracks, incomplete penetration,poor bonding (fusion), porosity andundercuts.

Standards define weld imperfec-tions based on measurements ona cross section (figure 86) of theweld and observations on itsappearance.

An international nomenclature ofdefects has been established andis given in EN ISO 6520-1 (30)which lists 6 groups of imperfec-tions, as shown in table 53, p. 104).

GEOMETRICAL CHECKING OF WELDS

➤

➤➤

➤

➤

➤

➤

➤➤

Butt welds

dθ

s

rry

➤

➤

➤

➤

➤

➤

➤

s ry

θ

a

Fillet

Misalignment : dToe angles at base of bead : θToe radii at base of weld : ry

Misalignment : dToe angles at base of bead : θToe radii at base of weld : ry

All numerical values are expressed in degrees or mmFigure 86

(28) X-ray testing is not normallypossible on fillet welds. (29) According to NF A 09-120. Non-destructive tests. General principles ofdye-penetration testing. June 1984. ( 30) EN ISO 6520-1 Classification ofgeometric imperfections in metallicmaterials. Part 1: Fusion welding.

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11.1Common weld imper-fections

Table 54 lists the most commonimperfections together with theirlikely causes.

104

GROUPS OF WELD IMPERFECTIONSGroup Type of Imperfection

100 Cracks 200 Cavities and wormholes 300 Solid inclusions 400 Lack of fusion and penetration 500 Defects of shape 600 Sundry defects

Table 53

N° Type of Defect Likely Cause Photos of Imperfections101 Cracks Base alloy unsuitable

Poor choice of filler metalIncorrect welding sequenceExcessive clampingSudden cooling

104 Crater cracks Pass finished with sudden arc cutoff2012 Irregular wormholes Work inadequately degreased

Work and/or filler wire dirty or wetInsufficient protection by inert gas (low gas flow or leak in the system)Pass begun on cold componentHigh arc voltageWeld cooled too quickly

2014 Aligned wormholes Incomplete penetration (double pass)Temperature gradient between liner and work too abruptExcessive gap between edges of the joint

300 Solid inclusions Dirty metal (oxides, brush hairs) 303 Oxide inclusions Poor gas shielding

Metal stored in poor conditionsCastings

3041 Tungsten inclusions Electrode diameter too small(TIG) Poor handling by welder

Excessive current densityPoor quality of tungsten electrode

402 Incomplete penetration Inadequate cleaning (presence of oxide)Incorrect bevel preparation on thick work (too tight, excessive shoulder)Gap between workpieces too small (or incon-sistent) Low current, especially at the start of the seamWelding speed too fastHigh arc voltage

TYPICAL WELD IMPERFECTIONS

Defect 101

Defect 104

Defect2012

Defect 300

Defect 402

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11.2Effect of weld imper-fections on fatiguestrength

Some weld defects have a signifi-cant impact on the fatiguestrength of the weldment:

■ cracks (emergent or otherwise)and incomplete penetration arevery serious flaws, as shown bytests carried out on welddefects [5] (figure 87),■ defects of geometry, especiallysudden breaks in curves (angle at

the base of the weld seam, mis-alignment etc.) aggravate stressintensity factors.

6. WELDING

N° Type of Defect Likely Cause Photos of Imperfections4011 Lack of fusion High arc voltage

on edges Low current, especially at the start of the seamWork cold (difference in thickness between materials to be welded)

502 Excessive thickness Poor power control (poor U/I match)Welding speed too slow Poor edge preparation on thick workInsufficient starting current

507 Misalignment Work positioned incorrectlyIncorrect welding sequence

508 Angle defect Excessive welding powerIncorrect welding sequence

509 Collapse Wire speed too fastTorch speed too slowPoor torch guidance

602 Splatter (or beads) Incorrect arc controlProblem in electrical contact to ground

BUTT WELD IMPERFECTIONS

MisalignmentBlistersExcessive thicknessSide undercutsLack of penetration, exposedV-groove weld, no imperfection (reference)Double V-groove weld no imperfection (référence)Lack of penetration, exposed

5083 O∆σ = 90 MPa

MisalignmentBlistersExcessive thicknessSide undercutsLack of penetration, exposedV-groove weld, no imperfection (reference)Double V-groove weld no imperfection (référence)Lack of penetration, exposed

6061 T6∆σ = 99 MPa

103 104 105 106 107 Nb of cyclesEndurance limit (R = 0,1)

Figure 87

Table 54

Defect 402

Defect 502

Defect 507

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12.REPAIRS AND FIT-TINGS

European shipyards have respondedto needs for the maintenance andmodification of aluminium highspeed ships by adapting to and spe-cialising in this new activity [6, 7, 8].

These yards repair damage toships and modify onboard installa-tions. The very long service life ofaluminium ships means that fromtime to time they must be adaptedin line with changing conditions ofservice, new equipment must beinstalled etc.

Work on aluminium alloy struc-tures is based on classical sheetmetalworking operations as iscommonly carried out on steelships (and their equipment), e.g.sheet and plate cutting, preparingedges for welding, making welds,correcting distortion etc.

The rules discussed previously foraluminium alloy forming and weld-ing apply equally to these opera-tions.

A number of basic precautionsshould be taken when weldingitems that are being repaired ormodified:■ clean surfaces near to the weldwith great care, using a brush toremove all traces of paint, oil or fuelthat could have fouled the plates,■ dry thoroughly before weldingto remove all traces of moisture,■ weld under cover of weatherand away from draughts; if neces-sary, work under a tarpaulin whenthese operations are carried outin dock,■ pay particular attention to thedirection in which welds are made– this will limit distortion and mini-mise the risks of hot cracking dueto shrinkage,■ select the correct welding pro-cess: TIG (for work less than 6 mm

thick) or MIG. TIG is more suitablefor minor repairs where backaccess is difficult or impossible,being easier to use in such situa-tions and providing better controlof penetration than MIG.

For localised repairs such as a tornhull, the repair patch must be per-fectly matched to the shape of thetear but will be bigger (achieved byhammering) to compensate forthe contraction caused by weld-ing. Without this precaution, theresidual stress would attain a levelwhere it would cause systematiccracking. The smaller the patch,the more pronounced this phe-nomenon.

Important note: Never work with a torch or electricarc on or in any enclosed space,tank etc. that has held water(including seawater) or which hasbeen in contact with moisturewithout first airing or thoroughlyventilating it to disperse the hydro-gen produced by possible corro-sion of the metal in contact withwater. Failure to take this precau-tion may lead to an explosion haz-ard with consequences that couldprove catastrophic for the opera-tors (31). It is also a mandatoryprecaution for any work on fuel oiltanks.

13.LASER WELDING

Since the early Nineties, the usesof welding by laser (32) havespread widely in shipbuilding [9].

13.1Principle of the laser

The laser is a device that gener-ates an intense beam of coherentmonochromatic radiation. In weld-ing machines, this radiation is con-centrated to obtain power densi-ties in excess of 106 W.cm-2 whichis sufficient for the industrial weld-ing of aluminium alloys.

This power is used to generate acapillary filled with metallic vapourwhose walls are lined with liquidmetal in fusion. The resulting weldpool bath is displaced and the liq-uid metal solidifies after the beamhas passed, ensuring metallurgicalcontinuity between the work-pieces (figure 88).

13.2Welding lasers

Two types of industrial laser areused for welding metals:

■ in CO2 lasers the activemedium is a gaseous blend of car-bon dioxide (CO2), nitrogen (N2)and helium (H2) at low pressure.The wavelength of the laser beamis 10.6 µm. Industrial CO2 laserscan generate power ranging from1.5 to 40 kW. The beam is trans-mitted by mirrors.

(31) The amount of hydrogen that buildsup in a ballast tank can be considerableeven though corrosion is only superficial.In a tank with sides 1 metre long forexample, i.e. 5 m2 of area in contactwith water, superficial corrosion onemicron deep releases 16.8 litres ofhydrogen !!!32) Light Amplification by StimulatedEmission of Radiation.

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■ in Nd:YAG lasers (NeodymeYttrium Garnet), the activemedium is a solid and the radiationwavelength is 1.06 µm, with amaximum available power of 3 to4 kW. Despite their low power,Nd:YAG lasers offer a number ofadvantages over CO2 lasers: thesources are more compact, andNd:YAG beams can be carried byfibre optics which makes it possi-ble to weld along complex pathsusing welding robots.

13.3Laser welding of alu-minium alloys

Aluminium alloys can be laserwelded with no particular difficultyand at speeds as high as severalmetres per minute.

Laser welding offers a number ofadvantages :■ simplicity of preparation beforewelding,■ high welding speeds, severalmetres/minute on butt welds in 6mm plate made from 5000 alloy,■ reduced distortion owing to thehigh welding speed and narrow-ness of the weldment,■ high penetration by the beam; itis possible to weld (CO2 laser)5000 series plate up to 12 mmthick in a single pass,■ high mechanical properties ofthe weld: nearly 90 % of theparent metal on 5083 H116 and70% for 6082 T6,■ different thicknesses can bewelded,■ ‘invisible’ welding,■ good final condition (minimalfinishing required),■ advanced automation.

Nevertheless laser welding requiresclose preparation tolerances andits energy efficiency is low.

13.4Laser weldability of aluminium alloys

Aluminium alloys have a relativelylow light absorption rate in the far-infrared: 3 % with the CO2 laserand 25 % with the Nd:YAG laser.However this coefficient of absorp-tion rises rapidly above fusion tem-perature and is approximately 90% when the material’s vaporisationtemperature is reached (figure 89).

For welding therefore, vaporisa-tion of the metal must be initiatedin the laser beam. Two very differ-ent types of interaction areobserved according to the powerdensity at the surface of the mate-rial (figure 90) :

6. WELDING

LASER WELDING

HAZ

Laser beam

Capillary

HAZ

Resolidifiedmoltenmetal

➤

➤

➤

➤

Laser beam

Upstream weldpool

Capillary full offmetallic vapour

➠Weldin

gdire

ction

Figure 88

COEFFICIENT OF REFLECTIONOF LASER BEAMS

100806040200

Tf Tv T

Coeff

icient

of ref

lectio

n of la

ser b

eams

λ = 10,6 µ (CO2)

λ = 1,06 µ(Nd : YAG)

%

Tf : fusion temperatureTv : Vaporisation temperature

Figure 89

INTERACTION BETWEEN LASER BEAM AND ALUMINIUM

➤ ➤ ➤

Fusion zone Fusion zone Fusion zonePlasma Absorbent plasma

Beam Beam Beam

p < 106 W/cm2

Surface fusion over some tens

of microns

106 < p < 107 W/cm2

Formation of« Keyhole » (optimum)

p > 107 W/cm2

Screen effect

Figure 90

➤

➤

➤

Downstream weld pool

Welding direction

➤

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■ at low densities, fusion is verysuperficial,■ at high densities a vapourcapillary forms, i.e. a narrow anddeep zone of fusion in the metal. Itis this interaction which is neededfor welding.

The threshold of interaction, i.e.the power density needed to forma vapour capillary, is of the order of106 W.cm-2. The value of thisthreshold depends on the compo-sition of the alloy – alloys that con-tain magnesium in the 5000 series(5754, 5083, 5086, etc.) have alower threshold of interaction thanother alloys (figure 91) and can bewelded with less power.

It is important to note that usingtoo high a power density iscounter-productive as the metalvapours will form a plasma thatacts as a shield. This is particularlytrue of CO2 lasers.

A shielding gas must be used toprevent the immediate oxidationof the weld pool, and with CO2lasers the best results areobtained with argon/helium blendsor pure helium. Argon can also beused with Nd:YAG lasers.

14.FRICTION STIR WEL-DING (FSW

Friction welding with a tool (33)was invented by the TWI (34), thefirst patent being filed inDecember 1991 [10].

It is clear that this has been a deci-sive advance in the joining of met-als in general and aluminium alloysin particular. In under ten yearsthis new welding technique hasenjoyed significant industrialdevelopment and growth in anumber of sectors including ship-building, aerospace and the rail-ways [11].

Since 1995 many publicationshave appeared and presentationsgiven on the applications of FSWwelding in shipbuilding at interna-tional conferences on High SpeedShips made from aluminium [12].These publications reflect theobvious interest shown by navalarchitects and yards in this newtechnique, one which is alreadymaking very significant changes toaluminium shipbuilding and givingit fresh impetus [13, 14].

14.1Principle of frictionstir welding

The process is a simple one, con-sisting of shearing the metal with-out melting it (it turns ‘pasty’) witha rotating tool that has a ‘probe’ orpin on a level slightly below that ofthe weld. As it rotates the toolstirs the metal of the workpiecestogether and discharges it to therear where the weld thus formedis softened and consolidated.

The metal is made to flow by theheat from the friction of the rotat-ing shoulder against the surface ofthe metal. The shoulder, which islarger in diameter than the probe,contains the moving particles ofmetal and maintains a pressurethat prevents the metal frombeing ejected outside the weldedzone (figure 92).

The very significant forces that areexerted on the work mean that itmust be clamped very firmly tothe table of the welding machine.

14.2Microstructure of the FSW joint

The specific properties of the FSWjoint are due to its microstructurewhich is very different from themicrostructure of an arc weld(MIG or TIG) owing to the simplefact that there is no process offusion / solidification. An FSW weld has four very dis-tinct zones (figure 93) [15] :

■ zone A, outside the weld, is theparent metal of each of the work-pieces on either side of the joint.Its structure is unaffected by wel-ding,■ zone B is the heat affectedzone. It does not undergo anyplastic deformation. As with theHAZ of conventional MIG or TIGwelds, its mechanical properties

THRESHOLD OF LASER INTERACTION

Pene

tratio

n de

pth

mm2

1

0

Specific power in focal plane lm1 2 3 4 5

106W/cm2

Welding speed Vs = 6 m/minFocusing plane ∆z = + 0,5 mmFocal length f = 150 mmConvergence factor F = 5,0Radius of final point rf = 136 µm

–– 5182 –– 5754 –– 6082

Figure 91

(33) Friction stir welding (FSW). (34) TWI: The Welding Institute.

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are low (figure 94). This zone isannealed in strain hardened alloysand over-aged in age hardenedalloys (35). However no deforma-tion occurs because the heatingup of the metal and the tempera-ture level attained are much lowerthan in arc welding,■ zone C is the thermomechani-cally affected zone that has under-gone plastic deformation and hea-ting. The structure of this zonedepends on a number of parame-ters including the type of alloy,■ zone D is the “nugget” formedfrom recrystallised grains in whichthe metallurgical constituents ofthe parent alloys are dispersed.The grains are usually smaller thanin the parent metal. This structureenhances the fatigue resistance ofthe welded joint.

In age hardened alloys the nuggetis in a condition close to T4 (solu-tion heat treated, natural ageing atambient) (figure 95).

14.3Comparisonswith arc welding

The FSW process operates at atemperature below the meltingpoint of the metal, offering anumber of advantages:

■ conditions of use are simpli-fied: surface preparation is confi-ned to degreasing only. Whereedge preparation is necessary,surfacing is adequate. The processrequires no filler metal or shieldinggas,■ the applications of FSW are farmore extensive than with arc wel-ding: all types of aluminium alloyproducts can be welded, whethercastings or wrought semis, ■ the quality of the weld: thereare no risks of hot cracking (36) orporosity as hydrogen is not for-med (37),■ the quality of the assemblies:distortion is minimal owing to thelow temperature levels and thefact that welding takes place in asolid medium,

6. WELDING

FRICTION WELDING TOOLS

➠

➠

Downward forceTooladvance

Probe

Trailing edge of tool

Shoulder

➤

➤

➤

Weld

➤

Figure 92

MICROSTRUCTURE OF THE FSW JOINT

A : Parent metal unaffected by weldB : Heat affected zone (HAZ)C : Unrecrystallised area found in aluminium alloysD : Recrystallised nugget found in aluminium alloys

Width of tool shoulder➤

➤

CC DBA B A

CHANGE IN HARDNESS IN THE HAZ OF 5083 [15]

100

90

80

70

60-40 -30 -20 -10 0 10 20 30 40

Hardn

essH

b

Distance from weld centre (mm)

5083 O5083 H321

CHANGE IN HARDNESS IN THE HAZ [16]

1201008060402000 10 20 30 40

Centre of weld6082 T6

As weldedaged 3 h at 185 °C

Hardn

essH

b

Distance across weld (mm)

1201008060402000 10 20 30 40

Centre of weld6082 T4

As weldedAged 3 h at 185 °C

Hardn

essH

b

Distance across weld (mm)

Figure 93

Figure 94

Figure 95

(35) As a result the alloys are in themetallurgical condition indicatedpreviously.(36) It is possible to weld copper alloys(2000 and 7000 series).(37) If hydrogen did form it would not bedissolved because its solubility in solidaluminium is zero.

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■ environmental and workingconditions: there are no fumes,no flying particles of metal, noozone emissions and no ultravioletradiation. The process is alsoenergy efficient, requiring about20 % of the power of MIG wel-ding.

Its present state of industrialdevelopment makes FSW highlysuitable for prefabricating sub-assemblies such as deck sections,walls, panels etc. [17] in the work-shop for subsequent installation inships and assembly by conven-tional welding techniques such asMIG (38).

A prototype “portable” machinedesigned by the University ofAdelaide in Australia with TheWelding Institute was presentedrecently [18]. This is in fact a toolconnected to a hydraulic motorand mounted on a trolley for weld-ing hull plates 5 mm thick.However although the tool is“portable”, the components to bebutt welded must be firmly fixedto withstand the forces necessaryfor welding.

14.4Possibilities of wel-ding with FSW

In its present state of advance,FSW allows the welding of mate-rial up to 25 mm thick. Researchinto 6000 series alloys has shownthat it is possible to go up to 50mm thick with a single head (fig-ure 96), and 75 mm with twoheads (figure 97).

Given the current level of industrialdevelopment of the process, FSWcan be envisaged in a number ofconfigurations for butt welds and‘invisible’ welds as shown infigure 98.

(38) A welding code is in the process ofbeing approved by the classificationsocieties.

TOOL WHORLTM

75 mm section of 6082

FSW WELDING WITH TWO HEADS

Adjustable roller guides Contra rotating tools

TYPICAL FSW WELD CONFIGURATIONS

➤

a b c

d e f

a : Butt weldb : Invisible weldc : Invisible weld in several

thicknesses

d : Welding brackets in Teee : Invisible Tee weldf : Fillet weld inside

Figure 97

Figure 96

Figure 98

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14.5Performance of FSW welds

There have been numerous stud-ies characterising the properties ofFSW welds – their mechanicalproperties, fatigue strength andcorrosion resistance of the weld-ment [19].

■ Mechanical propertiesThe mechanical properties of FSWwelded metal are superior to thoseof MIG welded metal (table 55).

Fractures usually occur at theedge of the friction zone, neverinside it, most probably becauseof the strain hardening caused bythe base of the tool.

The limit of elasticity is at least10% higher in FSW welded metalthan MIG welded.

■ Fatigue resistanceThe limit of endurance of FSWwelded metal is superior to that ofa MIG weld (figure 99) [21].

The limit of endurance of an FSWweld is always superior to that of aMIG welded joint, and this is true

for all alloys. This is because FSWensures a very good connectionbetween the joined workpieces.There is no ‘sticking’ (i.e. lack offusion). It goes without saying thatthis applies only when the FSWjoint is free from imperfections.

■ Corrosion resistanceInvestigations carried out so farhave not indicated any particularsensitivity to corrosion by FSWwelds. Their resistance to corro-sion is at least equal to that of MIGor TIG welds.

6. WELDING

Alloy Welding Rp0,2 (MPa) Rm (MPa) A % 5083 H116 MIG 134 287 12,8

FSW 157 335 17 Sealium® MIG 150 308 13,5

FSW 165 354 17

MECHANICAL PROPERTIES OF WELDED 5083 AND 5383 6 MM THICK [20]

Table 55

LIMIT OF ENDURANCE ON 5383 (AT 107 CYCLES FOR R = 0.1) [11]

Alloy Welding Limit of Endurance (MPa)Sealium® Parent metal 228

FSW 172 MIG 144

Table 56

MPa

N

➤

➤

➤

400

100

50

20104 105 106 107 3.107

5083 plate5083 welded

Recommendations ECCS,class B3

Stres

sran

ge

LIMIT OF ENDURANCE OF FSW JOINTS

Figure 99

ENGINE AND DRIVE SHAFT BEARER

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15.STANDARDS

The main standards that governthe welding of aluminium arelisted in table 57..

Reference Date Subject

BS EN 1011-4 Dec 2000 Welding. Recommendations for welding of metallic materials. Part 4: Arc welding of aluminium and aluminium alloys.

NF A 89-310 April 1973 Aluminium et alliages d'aluminium - Soudage - Assemblages élémentaires types - Critères de choix.

NF A 87-010 April 1973 Aluminium et alliages d'aluminium - Soudage - Préparation des bords.BS EN 288-4/A1 August 1997 Specification and approval of welding procedures for metallic materials.

Welding procedure tests for the arc welding of aluminium and its alloys.NF A 89-220 April 1973 Aluminium et alliages d'aluminium - Soudage - Classification et contrôle

des joints soudés.BS 8118 Structural use of aluminium. Part 2. Specifications for materials,

workmanship and protection.BS EN ISO 9692-3 Dec 2001 Welding and allied processes. Recommendations for joint preparation.

Part 3: Metal inert gas welding and tungsten inert gas welding of aluminium and its alloys. (ISO 9692-3:2000).

BS EN 12584 June 1999 Imperfections in oxyfuel flame cuts, laser beam cuts and plasma cuts. Terminology.

BS EN 30042 July 1994 Arc-welded joints in aluminium and its weldable alloys. Guidance onISO 10042 quality levels for imperfections.BS EN ISO 13919-2 Dec 2001 Welding -- Electron and laser beam welded joints -- Guidance on quality

levels for imperfections -- Part 2: Aluminium and its weldable alloys(ISO 13919-2:2001).

BS EN ISO 6520-1 Dec 1998 Welding and allied processes -- Classification of geometric imperfectionsin metallic materials -- Part 1: Fusion welding (ISO 6520-1:1998).

NF EN 83-100-1 Dec 1995 Construction d'ensembles mécano soudés. Techniques de soudage. Partie 1 – Généralités : Terminologie, Classes de qualité de soudure – Etendue des contrôles.

BS EN 12062 1998 Non-destructive examination of welds. General rules for metallic materials.

BS EN 970 May 1997 Non-destructive examination of fusion welds. Visual examination.NF A 09-120 June 1984 Essais non destructifs. Principe généraux de l'examen par ressuage.

MAIN EUROPEAN STANDARDS FOR WELDING OF ALUMINIUM

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Bibliography[1] “Soudure et chaudronneried’aluminium”, Revue de l’aluminium,No. 99, March 1938, pp. 1128-1135. [2] “Le soudage à l’arc des métauxlégers avec électrode fusible enrobée”,CHARLES GUINARD, Revue de l’aluminium,No. 167, June 1950, pp. 237-244.[3] “Die Fügetechniken des Aluminiumsim Laufe der Jahrzehnte“, G. AICHELE,Aluminium, Vol. 75, pp. 743-753, 1999.[4] “Construction of the All-Welded Twin-Screw Auxilliary Motor Yacht”, J. G.YOUNG, British Welding Journal, January1955, pp. 1-18.

[5] “Nocivité des de soudage suréprouvettes soudées MIG” D. ALBERT, C.HANTRAIS, M. MÉDIOUNI, M. TRICOT,Rapport Pechiney CRV 3535, December1994. [6] “Repair yards show their versatility”,Speed at Sea, April 1998.[7] “Routine repairs provide annualreturns”, Speed at Sea, January 1999.[8] “Aluminium skills are part of routineworkload”, Speed at Sea, October 2000.[9] “Developments in welding techniquesfor aluminium alloys”, J. D. RUSSEL, C. J.DAWES, R. L. JONES, TWI, ConferenceSouthampton 1996.

[10] “Improvements relating to frictionwelding”, W M THOMAS, E D NICHOLAS, JC NEEDHAM, MG MURCH, P TEMPLE SMITH,CJ DAWES, (TWI), Patent GB 91 25978.8,International PCT/GB92/02203 andEuropean Patent Specification 0 615 480B1.[11] “Application of Friction Stir Weldingfor manufacture of aluminium ferries”, S.W. KALLE, E. D. NICHOLAS, P. M. BURLING,TWI, 4th International Forum onAluminium Ships, New Orleans, May2000.

6. WELDING

Reference Date Subject

BS EN 1289 August 1998 Non-destructive examination of welds. Penetrant testing of welds. Acceptance levels.

BS EN 1712 Nov 1997 Non-destructive examination of welds. Ultrasonic examination of weldedjoints. Acceptance levels.

BS EN 1713 Sept 1998 Non-destructive examination of welds. Ultrasonic examination. Characterization of indications in welds.

BS EN 1714 Oct 1997 Non-destructive examination of welded joints. Ultrasonic examination of welded joints.

BS EN 1712/A1 February2003 Non-destructive examination of welds. Ultrasonic examination of weldedjoints. Acceptance levels.

BS EN 1714/A1 February 2003 Non-destructive examination of welded joints. Ultrasonic examination of welded joints.

BS EN 444 April 1994 Non-destructive testing. General principles for radiographic examination of metallic materials by X- and gamma-rays.

BS EN 1435 Oct 1997 Non-destructive examination of welds. Radiographic examination of welded joints.

BS EN 12517 Sept 1998 Non-destructive examination of welds. Radiographic examination of welded joints. Acceptance levels.

BS EN 287-2 June 1992 Approval testing of welders for fusion welding. Aluminium and aluminium alloys.

BS EN 287-2/A1 August 1997 Approval testing of welders for fusion welding. Aluminium and aluminium alloys.

BS EN ISO 9956-10 Nov 1996 Specification and approval of welding procedures for metallic materials --Part 10: Welding procedure specification for electron beam welding.

BS EN ISO 9956-11 Nov 1996 Specification and approval of welding procedures for metallic materials --Part 11: Welding procedure specification for laser beam welding.

BS EN 12345 June 1999 Welding. Multilingual terms for welded joints with illustrations.BS EN 1792 2003 Welding. Multilingual list of terms for welding and related processes.

Table 57

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[12] “4th International Forum onAluminium Ships”, New Orleans, May2000“European Shipbuilding in the 21thCentury”, London, December 2000. “The Third International Forum onAluminium Ships”, Haugesund, May1998.“Lightweight Construction – LatestDevelopments”, The Royal Institution ofNaval Architects, London February 2000.[13] “Studies extend Friction Stir Weldingpotential”, Speed at Sea, October 1998,p. 45. [14] “Friction Stir benefits include costsaving”, P. HYNDS, Speed at Sea, October1999, p. 33.

[15] “Friction Stir Welding in aluminiumalloys, preliminary microstructuralassessment”, P L THREADGILL, TWIBulletin, Vol. 28 (2), March 1997,pp. 30–33 .[16] “Friction Stir Welding – Weldproperties and manufacturingtechniques”, Proc INALCO-7, CambridgeApril 1998, pp. 171–181. [17] “Application of prefabricated FrictionStir Welding panels in catamaranbuilding”, O. T. MIDLING, J. S. KVÄLE, S.OMA, 4th International Forum onAluminium Ships, New Orleans, May2000.

[18] “Exploiting friction stir welding inexplosevely-formed aluminium boat hullconstruction”, I. HENDERSON, Joints inaluminium, INALCO 98, 1998, pp. 261-267.[19] “Friction Stir Welding – The state ofthe art”, P. L. THREADGILL; Report TWI7417.01/99/1012 [20] Pechiney Report CRV February 1999.[21] “Friction Stir Welding aluminiumalloy 5083, Increased welding speed”, C.J. DAWES, E. J. R. SPURGIN, D. G. STAINES,Report TWI 7735.1/98/993.2.

MARINA AT TRINITÉ-SUR-MER