US2385685A - Magnesium base alloy - Google Patents

Description

Patented Sept. 25, 1945 MAGNESIUM BASE ALLOY Robert s. Busk, Midland, Mich., asslgnorto The Dow Chemical Company, Mi

poration of Michigan dland, Mi'ch., acor- No Drawing. Application April 13, 1942, Serial No. 438,783

Claims.

The invention relates to magnesium base alloys and in particular concerns alloys of this nature having reduced burning or oxidation characteristics in the molten state.

Magnesium alloys are now widely used in the industrial and structural arts for forgings, castings, and extruded shapes where a light .weight metal having good strength properties is highly desirable. It is, of course, generally necessary to melt themagnesium as produced commercially and alloy it with other elements to give it the desired properties priorto use. Additionally, it may be necessary to remelt the so-formed alloy a number of times as when it is used for casting operations. It is well known that when magneslum and its alloys are handled in the molten state it is necessary to maintain the metal under a protective blanket of a suitable flux in order to control the oxidation and burning or the metal to the extent that it may be commercially used and, even then, an appreciable waste occurs due to burning. In case the materal is to be used in casting operations more waste occurs as the molten metal is ladled from the melting pot and poured into molds since this operation is carried out while the metal is in direct contact with air.

It is, therefore, the principal object of the invention to provide commercial alloys of magnesium exhibiting markedly decreased burning tendencies upon exposure to air.

Another object oi the invention is to provide magnesium base alloys which may be ladled in the molten state and poured into ingots without exhibiting marked burning tendencies.

Other objects and advantages of the invention I will be apparent as the description proceeds.

My invention is based on the discovery that the burning characteristics of some of the well known commercial magnesium alloys are greatly improved by alloying therewith a comparatively small amount of lithium. The quantity of lithium to be added -to produce the desired eiiect ranges between about 0.001 to 0.01 per cent. Specifically. it has been found that the effect oi the lithium is obtained in magnesium alloys in which aluminum, manganese, silver, and zinc are present either alone or in combination in the usual amounts for commercial alloys of magnesium containing these elements, such as from l-to 12 per cent of aluminum, 0.01 to 3 per cent of manganese, depending upon the amount of aluminum present, 1 to per cent of silver, and from 1 to 10 per cent of zinc, providing the magnesium content is maintained above about 80 per cent. In the case of manganese, it the amount of aluminum exceeds about Zr-per cent, more than about 0.5 per cent of manganese cannot be alloyed with the magnesium-aluminum alloy. It will be understood that these alloys may also contain the ordinary impurities that are found in the commercially known alloys, such as traces of iron, copper, nickel, and silicon.

Although the improved property of decreased burning of the new alloy is manifest over the entire range of composition indicated, a preferred quantity of lithium is about 0.005 per cent.

The following table compares a commercial al- 10y containing aluminum, manganese, and zinc having no lithium alloyed therewith with a siml6 ilar alloy containing 0.001 per cent of lithium.

Table. I

Per cent composition ma esium-rema det Crucible burning Ingot burning Al Zn Mn Li 1 o 2 0.2 Markedbuming.- Markedburning. 2 9 2 0.2 .001 Greatly improved lm rovod over over Example 1. xsmple 1.

. The tests labeled "Crucible burning" were made using alloys compounded .by adding the alloying 80' ingredients with stirring to a quantity of molten magnesium maintained under a suitable flux blanket. The test consisted in skimming the flux blanket from the surface of the melt and observing the comparative burning in the presence 5 and absence of lithium. In the case 01' the tests labeled Ingot burning" the molten metal, compounded in the foregoing manner, was poured into a suitable ingot mold and the. swim of the metal examined from time to time to determine 40 the degree of oxidation in the presence and absence of lithium.

It is clear from an examination of the table that the new alloy provides a distinct improvement as regards burning and oxidation over the well known commercial magnesium alloys. This improvement is observed in both the open crucible and when the metal is poured in ingot molds. Although the addition of the stated amounts o1 lithium greatly decreases the burning tendency of the noted alloys, it has been discovered that if the lithium content of the alloy exceeds 0.0l

per cent by any great amount, the burning characteristics of the known commercial alloy are not improved, but instead are deleteriously at- 56 iected to a very marked desree. Thus it is necesmelting and alloying metals with magnesium,

such as by adding the alloying ingredients as desired to-a bath of molten magnesium which is preferably protected from oxidation by providing a surface blanket of a suitable flux. It is be- 1 lieved that the flux should be substantially free from magnesium chloride if the highest alloying efllciency is to be obtained from the lithium.

I claim: 1. In a method of reducing the tendency to burn of a magnesium base alloy in the molten state. the step which comprises incorporating in the alloy while molten lithium in an amount from about 0.001 to 0.01 per cent of the weight of the alloy.

2. A magnesium base alloy containing from 0.001 to 0.01 per cent of lithium, said alloy being additionally characterized by a reduced tendency to burn compared to a similar alloy not containing lithium in'the aforesaid proportions.

3. The method of reducing the burning characteristics in the molten state of a magnesium base alloy' containing from 1 to 10 per cent of aluminum, from 1 to 10 per cent of zinc, and from 0.1 to 3 per cent of manganese, the total of the alloying metal not exceeding 20 per cent and the balance being magnesium, which comprises incorporating in the alloy in the molten state from 0.001 to 0.01 per cent of lithium.

4. The method of reducing the burning characteristics in the molten state of a magnesium base alloy containing from 1 to 10 per cent of aluminum and from 0.1 to 3 per cent of manganese, the balance being magnesium, which comprises incorporating in the alloy in the molten state from 0.001 to 0.01 per cent of lithium.

5. The method of reducing the burning characteristics in the molten state of a magnesium base alloy containing from 1 to 10 per cent of ;aluminum, from 0.1 to 3 per cent of manganese, and from 1 to 10 per cent of silver, the total of -the alloying metal not exceeding 20 per cent and the balance being magnesium, which comprises incorporating in the alloy in the molten state from 0.001 to 0.01 per cent of lithium.

ROBERT S. BUSK.