hot working of alnico 5 alloys

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Hot Working of Alnico 5 Alloys C. L. Kolbe and D. L. Martin Citation: Journal of Applied Physics 31, S84 (1960); doi: 10.1063/1.1984614 View online: http://dx.doi.org/10.1063/1.1984614 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/31/5?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Microstructure and domain studies in Alnico 5 and Alnico 7 (abstract) J. Appl. Phys. 57, 4173 (1985); 10.1063/1.334654 Intercrystalline Fracture in Alnico 5 J. Appl. Phys. 37, 1106 (1966); 10.1063/1.1708355 Microstructure of Alnico Alloys J. Appl. Phys. 37, 1100 (1966); 10.1063/1.1708351 Reversibility of the Coercive Force in Alnico 5 J. Appl. Phys. 27, 1250 (1956); 10.1063/1.1722242 Shape and Crystal Anisotropy of Alnico 5 J. Appl. Phys. 26, 1217 (1955); 10.1063/1.1721876 [This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP: 137.189.170.231 On: Fri, 19 Dec 2014 17:36:51

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Page 1: Hot Working of Alnico 5 Alloys

Hot Working of Alnico 5 AlloysC. L. Kolbe and D. L. Martin Citation: Journal of Applied Physics 31, S84 (1960); doi: 10.1063/1.1984614 View online: http://dx.doi.org/10.1063/1.1984614 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/31/5?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Microstructure and domain studies in Alnico 5 and Alnico 7 (abstract) J. Appl. Phys. 57, 4173 (1985); 10.1063/1.334654 Intercrystalline Fracture in Alnico 5 J. Appl. Phys. 37, 1106 (1966); 10.1063/1.1708355 Microstructure of Alnico Alloys J. Appl. Phys. 37, 1100 (1966); 10.1063/1.1708351 Reversibility of the Coercive Force in Alnico 5 J. Appl. Phys. 27, 1250 (1956); 10.1063/1.1722242 Shape and Crystal Anisotropy of Alnico 5 J. Appl. Phys. 26, 1217 (1955); 10.1063/1.1721876

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Page 2: Hot Working of Alnico 5 Alloys

84S K. ]. KRONENBERG AND M. r\. BOHLMANN

measurements in the light of Neel's theory suggest a grouping of reversing portions of the magnet into larger cooperating regions. This agrees with earlier findings obtained by observing colloid patterns. 5 To explain

5 R. K. Tenzer, Proceedings of Conference on Jifagnelism and Jllaterials, AlEE Spec. Publ. T-91, pp. 203-211.

relatively large domain-like regions of reversal w h_~ h .. , e '''llII

to assume t at magnetic regIOns cooperated durin be magnetization reversal. The stability behavi g t oriented barium ferrite suggests similar condition:

r tf

tends to confirm our assumptions of domain groups ~ versing cooperatively. r-.

J 0 U R :\ .\ L 0 F .\ P P LIE D PH Y SIC S SCPPLEMENT TO VOL. 31. :\0. 5 MAY. 19611

Hot Working of Alnico 5 Alloys

C. L. KOLBE AND D. L. MARTIN

General Electric Research Laboratory, Schenectady, New York

Alnico permanent magnet alloys have been successfully shaped into rod, wire and strip by hot working at elevated temperature. It has been found that by careful processing, certain Alnico alloys can be fabricated by extrusion, swaging, and rolling. The wrought Alnico after heat treatment was found to have comparable permanent magnet properties and improved mechanical properties compared to cast specimens of the same alloy.

INTRODUCTION

AL~ICO magnets are made commercially by casting molten metals or by pressing and sintering of

powders. The brittleness of these alloys, which makes them unworkable at room temperature, and moderately high temperatures, is associated with a two-phase microstructure.

At a high temperature the Alnico alloys usually transform into a ductile body-centered cubic phase. This transformation is the basis of the successful hot fabrication of Alnico. In practice, the solution to the hot shaping problem is more involved because of the effect of alloying elements on the phase fields, and the effect of impurities, segregation, etc. on the workability.

Alnico-type alloys have been successfully hot de­formed before. Bieberl added 2% titanium to a 25 Ni, 9 AI, 64 Fe alloy and hot forged to !-in. fiats. He also added titanium to Fe-Ni-AI-Co alloys2 and hot rolled to i-in. strip. Finch and WhiteS hot forged Fe-Ni-AI­Co-Cu alloys containing 4.8% vanadium. Hansen4 de­scribes successful 180° hot bend tests on alloys to which titanium and zirconium had been added. The alloys covered in these three investigations were of the Alnico 1-4 types with energy product values under 2 million gauss-oersteds in contrast to values of 4-5 million gauss­oersteds reported in the present investigation.

Earlier studies by R. Ahles, W. Reich and R. lVIcKechnie5 in General Electric had established the

1 C. G. Bieber, lPermanent Magnet, U. S. Patent 2,285,406 (1942).

2 C. G. Bieber, Alloy for Permanent Magnet, U. S. Paten,t 2,384,450 (1945).

3 O. J. Finch and J. H. White, Permanent Magnet Material, U. S. Patents 2,347" 817 and 2,349, 857 (1944).

4]. R. Hansen, Permanent Magnet and Magnets Therefor, U. S. Patent 2,499,862 (1950).

5 R. Ahles, W. Reich, and R. McKechnie (private communica­tions).

workability of Alnico 5 alloys. This present study is an extension of their work and includes several of the alloys melted by R. McKechnie.

EXPERIMENTAL

~lore than forty compositions were prepared and evaluated for their hot fabrication characteristics. Iu this paper only a general summary of results is given. The twelve alloys listed in Table I to illustrate our ob­servations are divided into four groups: The first, Nos. 1-3, second, Nos. 4--8, and fourth, Nos. 11-12, groups are vacuum melted. Groups two and three, Nos. 4--10, contain zirconium additions, and the fourth group has high cobalt-titanium Alnico 10 modifications (Ticonal X).

Extrusion

In the early experiments it was found that the alloys containing zirconium successfully extruded at low tem­peratures in the range of 1050-1100°C. Sounder bars with fewer surface cracks were obtained than with the straight Alnico 5 composition.

An improved surface condition of the extruded bars was obtained by encasing the billet in a steel jacket. In one case (Alloy 9) the surface cracked badly when the alloy was extruded bare, 'but had a crackfree surface when re-extruded within a steel jacket. A heavy steet jacket is not necessary. A wall thickness of i in. was found satisfactory.

Extrusion Was a method of preconditioning prior to further working by swaging or rolling. Extrusion, how­ever, is not a prerequisite for satisfactory swaging and rolling results. Cast bars of several alloys were swaged without prior extrusion (Alloys 5 and 11). .

While acceptable extrusions were obtained with. mr­melted as well as with vacuum-melted alloys, prOVIded

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HOT \\1 0 R K I X G 0 F A L .\; leo 5 .\ L LOY S 85S

TABLE 1. Chemical analyses and summary of fabrication results. The evaluation of fabrication is based on surface condition and soundness of the bar.

=== Alloy Chemical analysis~

no. :\1 Ni Co ~

1 7.9 14.9 23.5 2 8.1 14.3 25.9 3 8.9 14.1 24.0 4 6.9 14.3 24.6 5 7.4 14.5 24.0 6 7.6 14.3 23.6 7 7.8 14.4 23.7 8 9.3 13.6 23.4 9 7.6 13.8 24.2

10 8.1 14.3 23.9 11 6.7 14.8 34.4 12 6.7 15.1 33.7

• Balance of al1o:r is mainly iron. bA vacant space indicate~ 110 tests made. < Specimen was enca::;ed in steel jacket.

Cu Zr

1.1 nil 3.0 nil 2.1 nil 3.0 0.36 2.7 0.24 2.3 0.25 2.7 0.26 3.1 0.29 2.7 0.22 3.5 0.33 4.0 nil 4.1 . nil

the billets were jacketed, the best results in regard to all types of deformation were obtained on vacuum­melted material.

Swaging

The swaging tests ,vere conducted on cast and ex­truded samples. In general, the extruded bars swaged much better than the cast bars. Alloys 5 and 11 were two outstanding exceptions. These cast bars had ex­cellent working characteristics and swaged to wire without cracking. Alloys 8 and 10 extruded very well, hut could not be swaged without serious cracking. The smallest wire swaged was O.040-in. diameter. Below that size the wire lost heat too rapidly for successful swaging.

Rolling

Only a few attempts were made to roll Alnico. Those alloys whIch swaged well, such as Nos. 7 and 11, could also be hot rolled. Alloy 4 strip was hot rolled at 1050°C from ~-in. diameter rod to O.090-in. thick. It was possibl~" to make O.005-in. strip of Alloy 7 by pack rolling.

TABLE II. Comparison of peak permanent magnet properties of cast and swaged specimens.

~================================== Cast Swaged

Br He (BIJ) 111 X 106 Br He (BH,lmXlO" Alloy k". oe goe kg oe goe --" 1 12.8 585 4.8 12.3 585 4.5 i 12.6 580 4.7 12.5 590 5.1 11 8.5 1310 4.6 8.7 1260 4.4 12 85 1310 4.7 7.9 1240 3.5 ~

Type Evaluation of results!' of

Ti melt Extrusion Swaging Rolling

nil vac. Poor nil vac. Fair nil vac. Fair nil vac. Goode Excellent Excellcnt nil vac. Excellent nil vac. Fair Excellent nil vac. Good' Excellent Exccllent nil vac. Fair' Poor nil air Good' Good" nil air Poor Poor 5.0 vac. Excellent Fair 5.1 vac. Goode Good'

Discussion of Hot Working

Vacuum melting alloys were found to work better than air-melted alloys. The beneficial effect of zirconium and titanium may be related to their high reactivity with oxygen, sulfur, and other elements that could cause hot shortness; or perhaps these two elements cause a shift in the alpha-gamma phase boundary.

Encasing the billets in a steel jacket prevents a serious drop in the billets surface temperature and at the same time introduces a surface easier to lubricate.

Hot working refines the grain structure. The finer grained extruded bars were in general easier to swage. Wrought alloys ground to an improved surface smooth­ness, and had increased strength and toughness.

The results indicate that the alloys with aluminum higher than 8% did not work as well. This effect may be related to the generally poor workability of the high alloy binary iron-aluminum and nickel-aluminum alloys.

Magnetic Studies

Only a few of the wrought alloys were heat treated and tested for their magnetic properties. These are listed in Table II together with the peak properties ob­tained on the cast specimens of the same alloy. The results show comparable permanent magnet properties for the swaged bars.

ACKNOWLEDGMENTS

We would like to acknowledge the assistance of the following during the course of this program: R. :\IcKechnie, :\Iiss Eleanor Freeman, T. Doig, D. 'Wilkins and L. Hibbs.

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