US1845694A - Treatment of alloys - Google Patents

Description

mama Feb. 16, 1 32 UNITED STATES PATENT OFFICE 10mm 1. WOOD, 01' LLIIWOOD, OHIO, ASBIGNOB '1'0 comm 0! amazon, 0] PENNSYLVANIA, A. OODORATIOR OI rmsnvun mum on armors In Drawn. Application fled April 1,

The invention relates to methods of im proving the internal structure and mechanical properties of easily oxidizable metals,

. such as aluminum and magnesium, or the alloys of easily oxidizable metals.

It is known to the art that the easily oxidizable metals, when molten, have a tendency to absorb gases and hold them either in mechanical suspension or in solution, principally the latter. This absorption is particularly troublesome in connection with the melting of aluminum and magnesium. These gases inay come from various sources, usually mm the furnace atmosphere during melting of the metal and in maintaining its heat until pouring, but possibly also from the atmosphere or other source. It is known that hydrogen may penetrate even the pots in which the metal is being heated. In addition to hy drogen, certain other ases such as nitrogen, carbon monoxide, car on,dioxide methane, etc. have been noted by investlgators in studies of the gases absorbed by molten alloys of the light metals.

The greater part of such absorbed gas may be held in solution in the molten metal and as the metal cools it becomes super-saturated with respect to the gas. When a casting is poured, escapin gases are frequently observed to distur the surface of the molten metal in the gate but this never affords a complete method ofescape for all the gases in the metal and sometimes a casting solidifies while still retaining a large and injurious quantity of entrapped as. Occasionally, if a castin be fractured, t e cavities formed by gas bub les in the metal are visible to the naked eye, frequently the porosity from this source appears under the microscope, and, in many cases, there may be an appreciable amount of diffuse metallic unsoundness which, though submicroscopic, may be, under some circumstances, reflected either in reduced mechanical properties or unexpected failure of the article in service. In addition to being in'urious in a casting, entrapped.

or dissolve gases are very undesirable in r ingots which are subsequently to be worked n forming process.

1m. sem a. 557,057.

This invention is directed to a method of producing soundness in easily oxidizable metals and 1s particularly efiicacious in producmg internal soundness in articles fabricated from aluminu and magnesium and alloys of these metals. The invention resides in the discovery that if helium gas be passed through the molten metal before pouring into mgots or castings the subsequent articles are greatly improve and the gas content is considerably diminished.

A secondary-benefit arising from the treatment of the metal with helium resides in the fact that dross or oxide films suspended in ,the molten metal are caused to rise to the surface of the molten metal from whence they may be skimmed before pouring. Previously, such a method of removing dross skins has met with little success since an gases psed reacted injuriously with t e mo ten metal or dissolved, with the undesirable results mentioned hereinabove. Additional advantages resulting from ,the use of helium in the treatment of molten metal are that it is chemically inactive with respect to the metal, that it will-not ignite or explode on escaping from the surface of the metal, and, as I have discovered, it does not appear to dissolve in the metal but will carry out the other gases which are dissolved therein, with the efl'ect that the-resulting casting or ingot is considerably sounder than one not similarly treated.

The amount of improvement which can-be effected is dependent upon the previous condition of the molten metal. If extensive presuspended matter, the beneficial effect will not be so noticeable as if the metal has been prepared and melted under ordinary commercial conditions. It is economically'advantageous to eliminate tedious and expensive preliminary precautions and to subject the metal to the simple and relatively short treatment hereinafter described.

With aluminum base alloys which are particularly prone to dissolve gases, the principal function of the treatment seems to conp the surface of the metal.

Althou h I have found the treatment with helium a vantageous with a number of different alloys of the easily-oxidizable metals, I have found it of particular usefulness-in that type of alloy which contains substantial quantities of magnesium in an aluminum base. Alloysof this class have just recently come into commercial use by reason of new develo ments in their casting and fabricatin tec 'que and I have found their desirabIe properties to be markedly enhanced-by treatment. with helium.

: As an instance of the improvement roduced bylthe practice ofthe invention, a eat of an a oy of 10 per cent ma esium, balance aluminum, was prepare and, after pouring a number 'of test specimens for the purpose of comparison, the balance of the molten metal was given several treatments 'with helium gas. In Table I, A indicates the average physical properties of a number of specimens of the alloy from the melt-which was not treated with helium; B indicates the average properties of a number of specimens of the alloy from a portion of the melt through which helium gas had been bubbled for one minute; C indicates the average properties of a number of specimens of the alloy from a portion of the melt through which helium gas had been bubbled for two minutes; and D indicates the average properties of a number of specimens of the alloy from the portion of the melt through. which helium had beenbubbled for five minutes. After casting in sand, the specimens were heat treated for twenty hours at 800 Fahrenheit and quenched.

Table I Time of treatment Yield Tensile Per cent 11: 1a li nu ri 2 um per on gas in sq. sq. in. inches c aoo 000 as 1 It 100 2:: M 9. 0 2 25, M 40, (IX) 9. 2 5 27, mo 43, 000. 10. 0

, The results given in Table I indicate clearly the improvement in ,yield stress, tensile strength, and elongation as additional amounts of helium are passed through the molten metal. There is an increasing and marked beneficial effect. This beneficial effect does not continue'to increase in direct ratio to the amount of helium sup lied, since the dissolved gases and mechanica inclusions are rapidly removed and the molten metal is soon in the optimum condition for pouring. After a period readily determined by expennifent, further treatment has no appreciable e ect.

Table II contains results showing the efi'ect of helium treatment on the physical properties of an aluminum base alloy containing about 4' per cent copper. This metal was known to'be badly gassed and the treatment with helium was intended to restore, if possible, its ori 'nal properties. In the table, A

indicates t e result of tests on untreated Y metal and B indicates the result of on metal after a three-minute treatment with helium gas.

Any method or apparatus for molten metal with gas can be'used. I have found it convenient to use a tank of helium gas (which is obtainable commercially) by connecting the tank through a flexible hose to a section of heat resistant tubing which can be dipped into the molten metal. The molten metal may be conveniently stirred, using the tube as a stirring rod, while the gas bubbles through the molten metal. A short time, usually less than six or seven minutes, is sufli cient for small heats in the neighborhood of one or two hundred pounds of metal, but, in dealing with larger heats, itis well to extend (the time until experimentshows that all potential improvement has been effected.-

In this specification and in the appended claims, the term aluminum? defines both the metallic aluminum and aluminum base alloys in which the aluminum contentis more than 50 per cent while the term magnesium defines not only magnesium but magnesium al- L loys in which the magnesium content is more than about 50 per cent.

I claim: 1. The method of improving easily oxidizable metals, comprising treating the molten metal by passing therethrough helium gas.

2. The method of treating easily oxidizablemetals to remove therefrom dissolved gases and mechanical inclusions, comprising melting the metal and fluxing the molten metal with helium.

3. The method of improving the internal structure and mechanical properties of aluminum, comprising fluxing molten luminmn -v with helium as.

I 4. The met 0d of improving the internal 5 structure and mechanical properties of magnesium, com rising neslum with ehum fiuxing the molten mag- OBERT T. WOOD.