Chapter 11-16

• Particles impede dislocations.• Ex: Al-Cu system• Procedure: --Pt A: solution heat treat (get solid solution) --Pt B: quench to room temp. --Pt C: reheat to nucleate small crystals within crystals.• Other precipitation systems: • Cu-Be • Cu-Sn • Mg-Al

Pt A (sol’n heat treat)

Pt B

Pt C (precipitate )

Temp.

Time

Adapted from Fig. 11.22, Callister 6e. (Fig. 11.22 adapted from J.L. Murray, International Metals Review 30, p.5, 1985.)

Adapted from Fig. 11.20, Callister 6e.

PRECIPITATION HARDENING

300

400

500

600

700

0 10 20 30 40 50wt%Cu(Al)

L+L

+L

T(°C)

A

B

C

composition range needed for precipitation hardening

CuAl2

Chapter 11-16

PRECIPITATION HARDENING

Chapter 11-17

• 2014 Al Alloy:

• TS peaks with precipitation time.• Increasing T accelerates process.

• %EL reaches minimum with precipitation time.

Adapted from Fig. 11.25 (a) and (b), Callister 6e. (Fig. 11.25 adapted from Metals Handbook: Properties and Selection: Nonferrous Alloys and Pure Metals, Vol. 2, 9th ed., H. Baker (Managing Ed.), American Society for Metals, 1979. p. 41.)

PRECIPITATE EFFECT ON TS, %EL

precipitation heat treat time (h)

tensi

le s

trength

(M

Pa)

300

400

500

2001min 1h 1day 1mo1yr

204°C

149°C

non-

equi

l. so

lid s

olut

ion

man

y sm

all

prec

ipita

tes

“ag

ed”

fe

wer

larg

e

pre

cipi

tate

s

“ove

rage

d”%

EL

(2in

sam

ple

)10

20

30

0 1min 1h 1day 1mo1yr

204°C 149°C

precipitation heat treat time (h)

Chapter 11-18

• Peak-aged --avg. particle size = 64b --closer spaced particles efficiently stop dislocations.

Simulation courtesyof Volker Mohles,Institut für Materialphysik der Universitåt, Münster, Germany (http://www.uni-munster.de/physik/MP/mohles/). Used with permission.

SIMULATION: DISLOCATION MOTION PEAK AGED MATERIAL

Chapter 11-19

• Over-aged --avg. particle size = 361b --more widely spaced particles not as effective.

Simulation courtesyof Volker Mohles,Institut für Materialphysik der Universitåt, Münster, Germany (http://www.uni-munster.de/physik/MP/mohles/). Used with permission.

SIMULATION: DISLOCATION MOTIONOVERAGED MATERIAL

Chapter 11-20

• Steels: increase TS, Hardness (and cost) by adding --C (low alloy steels) --Cr, V, Ni, Mo, W (high alloy steels) --ductility usually decreases w/additions.• Non-ferrous: --Cu, Al, Ti, Mg, Refractory, and noble metals.• Fabrication techniques: --forming, casting, joining.• Hardenability --increases with alloy content.• Precipitation hardening --effective means to increase strength in Al, Cu, and Mg alloys.

SUMMARY