US2797161A - Magnet alloy - Google Patents

Description

United States.

2,797,161 MAGNET ALLOY No Drawing. Application September 3, 1953, Serial No. 378,396

1 Claim. c1. 75-124 This invention relates to improvements in magnet alloys of the type represented by the alloys known as Alnico V and Alnico VI.

In their general formula, the Alnico V and Alnico VI type magnet alloys contain from 6% to 11% aluminum, from 10% to 20% nickel, from 16% to 30% cobalt, and up to about 7% copper. High magnetic strength alloys of this general formula also contain small amounts of additive constituents, that is, up to about 1.0% manganese, and up to about 1.0% silicon. One of the higheststrength Alnico V alloys also contains a small percentage of zirconium. One of the highest-strength Alnico VI alloys contains, in addition, a small percentage of titanium. The balance, in each case, is substantially all iron.

It is an object of the invention to provide an improved magnet alloy having higher magnetic properties than have heretofore been obtained. It is an object of the invention to provide a magnet alloy having high magnetic properties in combination with desirable physical properties. It is an object of the invention to provide an alloy formula which will give magnets of the desired properties with a high degree of uniformity, and which will facilitate the regular commercial production of highstrength magnets of desirable physical properties. It is an object of the invention to provide a magnet alloy in which the presence of impurities, especially carbon, is less critical than has heretofore been the case.

In accordance with our invention, we include in the magnet alloy at small percentage of columbium, and preferably also a small percentage of sulphur. The columbium eliminates the need for zirconium, and we find that by the use of columbium instead of zirconium, we obtain improved results and provide an alloy of less cost than the known zirconium-containing alloys.

We find that the use of columbium, preferably also with sulphur, greatly improves the uniformity with which alloys of (this type can be produced. We find, especially with Alnico V alloys, that the use of columbium produces a magnet alloy of substantially improved magnetic properties. While with columbium alone, the alloy tends to give magnets of poor physical properties, which may be so brittle that they crumble during production grinding operations, the addition of sulphur with the columbium avoids such poor physical properties and gives an alloy of improved magnetic properties combined with adequate physical toughness.

In accordance with our invention, the amount of columbium included in the alloy can be between 0.05% to 1.0%, and preferably between about 0.05% and 0.4%. The amount of sulphur used is desirably at least one quarter the amount of columbium used, and can be between 0.01% and 0.3%, and preferably between 0.02% and 0.1%.

Our new magnet alloy containing columbium and sulphur provides higher magnetic properties than have heretofore been obtained with Alnico V alloys. It permits those increased magnetic properties to be obtained uniformly on successive heats, and provides an alloy of adequate strength and toughness, so that there is a substantial reduction in the amount of material lost as scrap. In addition, like the addition of zirconium, our

2,797,161 Patented June 25, 1957 use of columbium and sulphur permits a reduction in the percentage of cobalt and nickel from that required to obtain best results with the standard Alnico V alloy; and while columbium is itself more expensive than zirconium, the amount required is substantially less so that the cost of the added ingredient and of the over-all alloy is less than when zirconium is used. Further, we find that the use of columbium and sulphur permits the obtaining of good results even when carbon is present to a relatively high degree, say up to about 0.05%, so that there is a less critical necessity for extreme reductions in the amount of carbon present. Our new alloy does not require the presence of manganese, but a small percentage of manganese may be present.

The following Table 1 shows in column I the preferred range of constituents for alloys embodying our invention, and in column II a range which we have found to be most desirable:

TABLE 1 I Preferred Range, percent Constituents Aluminum Nickel- Cobalt Copper...

Carbon..- Manganese Silicon (Alnico V).

Titanium (Alnico VI) Columbium Sulphur 1 At least the amount of columbium.

Tests were made under conventional testing conditions of (A)The commercial zirconiumand silicon-containing Alnico V was selected for comparative purposes, as representative of the best available Alnico V alloy. Twenty-five heats of this alloy were used, having an average analysis as follows:

Aluminum 7.77%. Nickel .13.40%. Cobalt 22.70%. Copper 2.83%. Carbon Impurity, 0.026%. Manganese Impurity, 0.08%. Silicon 0.54%. Zirconium 0.26%. Columbium None. Sulphur None.

Tests of the twenty-five heats of this zirconiumand silicon-containing Alnico V alloy give results as shown in the following Table 2.

TABLE 2 Alnico V with zirconium and silicon Br He (BH) max.

High 13, 550 664 5. 76 LOW 12, 600 5. 15 Average 12, 800 630 5. 50- Pereent Range .8 11.3 11. 8

i In this Table 2, as in comparative tables given below,

Br represents the residual magnetism per unit of the test piece after the test piece has been magnetized to its maximum value and the magnetizing force then reduced tQ zero; Hc represents the value of the. dem'agnetizing force per unit of the test piece required to reduce the magnetizati'on of the test piece from its Br value to zero; .(BH) max. is the maximum product, .in millions, of B and H values at various points along the magnetization curve, and represents the amount of magnetic energy that eachcubic centimeter .of the test material is capable of supplying; the big values are the highest obtained with any test piece of the series; the low? values are'the lowest obtained with any test piece of the series; .the average values are the average values of all the test pieces of the series; and percent range is the percentage of the rangeof values, i. e., the high value minus the low value, as compared to the low value.

B.--The Alnico V alloy containing silicon as its only additive was tested as a basis for comparison to show the effect of adding columbium and sulphur. Five heats of the silicon-containing Alnico V alloy were used. The same amounts and proportions of constituents were used in all five heats, and the five heats had the following average analysis: a

7 Percent Aluminum 7.63 Nickel 13.14 Cobalt 22.53 Copper 2.76 Carbon ".028 Manganese .076 Silicon .446

Tests of the five heats of this silicon-containing Alnico V alloy gave the results shown in the following Table 3.

TABLE 3 Alnico V with silicon alone Br He (BH) max.

High 13, 400 616 5. 64 Low 12, 200 565 3. 76 Average 12, 720 592 4. 87 Percent Rang 9.8 9.0 50

C.The Alnico V alloy containing columbium and TABLE 4 Heat NO. Al Ni Cu O Mn Si S Cb Charge 8 13.4 24 3 .47 .05 .10 2009 7. 86 13. 52 23. 21 3 06 04 08 49 031 1 Represents amount charged, not analysis result.

Permeameter test bars were castfrom these eleven columbiumand sulphur-containing Alnico V heats, were heat treated by standard AlnicoV treatment, and were (Table 3 then tested, and gave the magnetic data shown in the following Table 5.

TABLE 5 Heat No. Br Ho (1311) max . 530 5. 77. 623 5.84 632 5. 83 544 5. 37 54s 5. 9a 635 5. so 638 5. 64 545 5. 75 510 5. 70 524 5. 71 53s 5. 95

These results are summarized in the following Table 6:

TABLE 6 Alnico V with Si, S, and Cb.

Br Ho (BH) max.

13, 550 648 5. 96 13,200 610 v 5.64 13,361 633 5.80 Bercent Range.. 2 7 6. 2 5.7

Samples of the eleven heats of the new alloy were tested for brittleness, and subjected to commercial working operations, and all were found to have good physical properties. All withstood the working operations, and none showed excess brittleness.

In comparison with Alnico V containing silicon alone the new columbium-containing Alnico V (Tables 5 and 6) is substantially improved. The high (BH) max. value was 5.96 as compared to 5.64, an improvement of 5.6%. The low (BH) max. value was 5.64 which was equal to the highest value obtained with the silicon-Alnico V. The average (BH) max. value was 5.80 as compared to 4.87, an improvement of nearly 20%. Moreover, the improved results were obtained uniformly, and the several heats of the new alloy were less subject to variation and gave substantially uniform high quality. Where the silicon-Alnico V heats varied over a range of of the low value, the several heats of the new alloy varied only 5.7%. The addition of columbium, with sulphur, thus not only gave higher strength magnet metal, but gave improved uniformity as between successive heats.

The new columbium-containing Alnico V (tables 5 and 6) is also substantially improved over the zirconium-containing Alnico V alloy (Table 2) which represents the highest-strength material heretofore available. The high and low (BH) max. values of the new alloy are substantially higher than the corresponding values for the zirconium-containing alloy. The lowest value obtained with the new alloy was only about 2% below the highest value obtained with the zirconium-containing alloy. The new alloy gave an average (BH) max. value 5.5% higher than the zicronium-containing alloy. The new alloy gave much more uniform results, and the range of variation of results was less than half that obtained with the zirconium-containing alloy.

' These improved results were obtained with a charge of only 0.10% of columbium, whereas the best available previous alloy contained 0.26% of zirconium, which is more expensive than the 0.10% of columbium. The new alloy was improved in magnetic properties, was obtained more uniformly, and was less in over all cost.

The improved Alnico V alloy, of the formula shown in Table 4, has been repeatedly made in regular commercial production, where a zirconium-containing Alnico V had previously been manufactured with the same facilities and under the same general conditions. It has been found that the new columbium-containing alloy not only gives an improved product, but that the results of commercial manufacture are substantially more uniform than occurred with the zirconium-containing alloy. A similar comparative experience has been had with the Alnico VI alloy, and it has been found similarly that there was a substantial improvement in the uniformity of commercial production when the columbium-containing alloy was used instead of the zirconium-containing alloy.

We claim as our invention:

A permanent magnet consisting of an alloy containing from about 7.4% to about 8.5% aluminum, about 12.5% to about 14% nickel, about 21.5% to about 24% cobalt, about 2.5% to about 3.5% copper, about 0.4% to about 0.7% silicon, 0% to about 1.5% titanium, at

References Cited in the file of this patent UNITED STATES PATENTS 2,229,065 Franks Jan. 21, 1941 2,395,285 McKibben Feb. 19, 1946 2,499,861 Hansen Mar. 7, 1950 2,694,166 Hadfield Nov. 9, 1954