US2461229A - Method of producing magnesium base alloys - Google Patents

Description

Patented Feb. 8, 1949 METHOD OF PBGDUCING. MAGNESIUIVI BASE ALLOYS Alfred .lohn Murphy, Petts Wood,

James Malcolm Payne, assignors to Magnesium don, England, a company of Great Britain:

No Drawing. Application July 4, 1945, Serial No.

1 Claim. 1

This invention relates to improvements in magnesium alloys and the manufacture thereof.

A serious difficulty in the practical manipulation of magnesium-cerium-zirconium alloys in the foundry is the reactivity of cerium and zirconium with the fluxes normally used to protect molten magnesium alloys. This reactivity gives rise to erratic and expensive losses of cerium and zirconium when the alloys are melted for casting.

In order to avoid these difiiculties the present improvements make use of the protection against oxidation conferred by the addition of beryllium to magnesium alloys. This protection is sufficlently efiective to allow the alloys to be melted in air without flux or with a greatly reduced proportion of flux, or without flux in an atmosphere containing a gas such as sulphur dioxide.

Processes for the production of binary alloys of magnesium and beryllium cannot be operated at present on an economic basis and according to the present improvements, therefore the beryllium is introduced through the medium of some pre-alloy made with a third metal, which can itself be alloyed with magnesium. It is also difficult, if not impossible, to cause alloying directly between magnesium and zirconium metal, and in this case also the present improvements provide for the making of a preliminary alloy of the zirconium with a third metal, other than magnesium. The nature of this third metal is restricted in the present connection, however, by the consideration that the beneficial grain-refining action of zirconium is prevented if certain specific metals are also present as alloying constituents. In carrying out this invention silver is adopted as a suitable third metal, for it can be alloyed with beryllium and also with zirconium and it does not interfere with the grain-refining influence of zirconium in magnesium alloys.

The improved procedure, then, is to prepare pro-alloys of silver with beryllium and with zirconium respectively. The silver-beryllium prealloy is added to magnesium which has been protected from combustion during melting as by flux in the normal manner or by any other suitable medium. Sufficient silver-beryllium alloy is added to introduce a proportion of beryllium in the order of 0.01 to 0.1 per cent. When the silver-beryllium has been incorporated in the magnesium the flux, if present, is removed from the surface of the molten metal which has now become, by virtue of its beryllium content, so resistant to oxidation that the protection of the flux or other covering is no longer required. The silverzirconium pro-alloy, in sumcient amount to inand Ronald New Malden,. England, Elektron Limited, Lon- Great Britain July 11, 194.4.

troduce about 0.75 per cent zirconium, is added to the melt, and finally the desired amount of cerium (between 1.0 and 4.0 per cent) as cerium metal (or mischmetall) or as ma nesium-cerium alloy is incorporated. The final product is thus a magnesium-base alloy containing silver, beryllium, zirconium and cerium. A typical composition is:

Per cent Silver 2 Beryllium 0.05 Zirconium 0.75 Cerium 3.0 Magnesium Remainder In any treatment the silver-zirconium alloy is proportioned so as to introduce an addition of zirconium equal to 0.1 per cent to 0.8 per cent by weight of the magnesium base. This introduction of zirconium would involve the introduction of silver in amounts between 0.5 and 5.0 per cent.

The functions of the constituent metals in this alloy are as follows: the cerium and zirconium together confer useful mechanical properties at ordinary temperatures and resistance to creep under load at elevated temperatures, the zirconium is particularly beneficial in refining the grain size, and the beryllium produces a high resistance to oxidation, enabling the alloy to be remelted without the use of fluxes, thus avoiding serious loss of the alloy constituents cerium and zirconium. The silver is present as a consequence of the method of producing the alloy but it has, incidentally, a beneficial effect in strengthening the alloy at ordinary and at elevated temperatures.

In some circumstances it may not be desired to forego the use of fluxes entirely in the manufacture of these alloys. It may not be convenient for example to protect the molten metal by sulphur dioxide or it may be desired to treat the metal with flux for the removal of dross. In such a case it would be permissible to use flux and to make good any loss of alloying constituent by an addition of such constituent at the end of the melting operations. The alloy thus prepared would still possess the advantage that it could be remelted for casting in the foundry without the use of protective flux.

The present improvements are not specially concerned with the method of making the prealloys of silver with beryllium and zirconium, but such pro-alloys can be produced conveniently by melting silver with massive beryllium on the one hand, and with zirconium metal powder or zirconium hydride powder on the other, in vacuo in a high-frequency electric furnace.

We claim:

Process for the manufacture of a, magnesium base alloy containing additions of cerium and zirconium, comprising melting a body of magnesium under protection of a flux cover, introducing into the molten body a. silver beryllium pre-alloy in such quantity as to incorporate in the base between 0.01 to 0.1 per cent by weight of beryllium, removing the flux cover from said body, introducing into said body a silver-zirconium prealloy, and finally introducing the desired amount of cerium.

ALFRED JOHN MURPHY. RONALD JAMES MALCOLM PAYNE.

REFERENCES CITED UNITED STATES PATENTS Name Date Gauthier Dec. 10, 1940 Number Number 15 Number Name Date Burkhardt Dec. 31, 1940 Sauerwald Jan. 14, 1941 Von Zeppelin et al. Mar. 18, 1941 Von Zeppelin July 29, 1941 Nelson et al Nov. 4, 1941 McDonald Jan. 13, 1942 Dallenbach Feb. 10, 1942 Sauerwald June 16, 1942 Beck Dec, 22, 1942 Stroup July 10, 1945 Willmore et a1 Aug. 21, 1945 FOREIGN PATENTS Country Date Great Britain Aug. 9, 1939 OTHER REFERENCES Alien Property Custodian application of Sauer- 20 Wald, Serial Number 369,749, published June 15,

1943 (abandoned).

Beck, Technology of Magnesium and Its Alloys, by F. A. Hughes and Co., London, England published 1940, page 317.