US2244146A - Alloy for making castings - Google Patents

Description

Patented June 3, 1941 2,244,146 ALLOY roa MAKING cns'rmos John P. Gerhauser, Alexandria, Ind, assignor to The Mantle Lamp Company of America, Chicago, 111., a corporation oi Illinois No Drawing. Application Apr-i126, 1940, Serial No. 331,153

2 Claims.

This invention relates to an improved alloy for making castings, particularly castings such as slush castings, where it is required that the casting alloy shall be of substantial strength and relatively fluid when molten, that castings made of it shall be free from deterioration with age, and that it shall be relatively cheap to produce.

Heretofore, a type of casting alloy has been considerably used for casting purposes and particularly for making slush castings, which is known as "white meta and consists substantially of 95% zinc and 5% aluminum. This alloy has met with some measure of success but its use has indicated the need for acasting alloy to serve the same and other purposes, that will remain unaffected by the effect of atmosphere, that will be stronger and preferably more fluid when molten.

Heretofore, lack of initial strength, and poor resistance to corrosion over a period of time due to crystal or grain growth and excessive intercrystalline corrosion, have been barriers to the use of said white metal for thin walled castings wherein considerable strength is required together with a definite resistance to atmospheric corrosion.

Attempts have heretofore been made. to overcome these inherent weaknesses of said white metal by the addition of other metals, particularly copper. Such zinc-aluminum-copper and other prior modified alloys have in some instances exhibited increased initial strength and increased resistnce to atmospheric corrosion, but the increased strength and resistance to corrosion have been obtained only at a sacrifice of the fluidity of the molten alloys. This lack of fluidity has prevented the application of the alloys last mentioned, to general use in making slush castings and die castings wherein fine detail must be reproduced and wherein the alloy must flow into minute crevices of the mold.

As far as I am aware, I am the first to produce an alloy adapted to commercial casting purposes and containing over 90% of zinc by weight, which is substantially stronger and substantially more fluid than said white metal, and

which is substantially free from crystal or grain growth and inter-crystalline corrosion under atmospheric conditions.

The present invention provides a casting alloy overcoming the objections referred to in said white metal, and is the result of combining zinc, aluminum; copper, and silicon in the casting alloy, in the ranges of proportions below given,

the amount of the copper employed being preferably not over 3% by weight, and the amount of silicon being preferably not over one-fourth A) of 1% by weight, to secure the desirable results of greater fluidity than said white metal when molten, greater strength, and substantially complete freedom from deterioration of castings made of the new al-ioy due to the action of the atmosphere, even over long periods of time.

In connection with said white metal, it has been found that two effects frequently take place in castings made from the alloy; first, grain growth, by which the grain size in the structure of the casting increases markedly from what it was immediately after the casting operation, with the result of very materially changing the internal structure of the casting and weakening it, and second. inter-crystalline corrosion, which has apparently resulted from the penetration into the structure of the casting, of corrosive elements in the atmosphere, so that in many cases the casting which originally was firm and relatively strong, becomes extremely weak and of fragile nature due to the corrosion, so that it may be crushed easily with the bare hands. In certain tests made to determine the effect of this corrosion, test bars cast of said white metal and consisting of approximately zinc and 5% aluminum by weight, were kept for 10 days in an atmosphere saturated with water at 98 C. and at the end of the tests the rods were found to have become entirely corroded throughout their structure with the result that they crumbled under slight pressure and fell apart and had no appreciable strength. Similar test bars cast from the alloy forming the subject of the present invention, when subjected to the same tests, showed no appreciable corrosion and were but slightly impaired in strength by the trea ment.

Where in the specification and claims I use the term fluidity and its variants in referring to an alloy, I mean the fluidity oi the alloy in its molten condition in readiness for a casting operation. I do not find it necessary to attempt to express the fluidity in absolute terms or units, as I have devised a simple means for showing the relative fluidity of various alloys and metals which is quite suflicient for present purposes. I have prepared a metal or heat-conductive mold having an elongated and slender cavity, the thickness of the cavity at its entry end being suilicient to freely receive the fluid alloy or metal and the thickness of said cavity at its other end being zero or substantially so;

from the entry end thereof toits other end. The

width of the mold cavity is preferably uniform ,or substantially so throughout its length, and

said width may be of any convenient amount and is preferably uniform. The mold is of Sep: arable parts to remove the cast wedges, the lengths of which indicate the relative fluidity of the alloys or metals used in making the wedges, the most fluid alloy or metal producing the longest wedge. In testing the fluidity of the different alloys examined in connectionwith producing the alloy of the present invention, I found that a mold constructed as described of steel and having a fiat-'side d-cavity of an inch thick at its entry end, zero thickness at its other end, 12 inches long and from 1 inch toU/ inches wide, servedthe purpose effectively. In making said fluidity 'tests', 'care was used to have the mold at the same startin temperature before casting the test wedge from each of the alloys to be'compared-and the mold-was pro ded with an admission pocket laterally displace from the upper end of the moldto insure entry of the molten alloy into the mold atsubstantialiy zero velocity. I

The casting alloy of the present invtion consists preferably of 91.8%'zinc, 6% aluminum, 2% copper, and .2% silicon, by weight. The marked advantages of the casting alloy are not limited to these exact percentages, but are observed to be present to a marked degree for-ranges of proportions of the constituent metals departing from the preferred composition stated, as follows: The

in the proportions referred to, is to produce a casting alloy having greater fluidity than, the said white metal, which is an advantage in providing freer flow into the molds and also in providingfor more perfect engagement of the casting alloy with the surface of the mold so that fine line detail may be employed on the mold surface and be accurately reproduced in the cast surface; the strength of the new casting alloy is substantially 50% greater than the strength of said white metal; the new casting alloy appears to be substantially free from grain .growth, that isto say; the granular internal structure of castings made of the alloy is preserved substantially unchanged for long periods of time in atmospheres and under temperature conditions found heretofore to have most deleterious effects on the structure of castings made from the white metal referred to. It should be noted that although the copper constituent in the new alloy appears to have the effect of increasing the strength of the alloy, it also, unless the effect were counteracted, would have the tendency of making the alloy when molten substantially more sluggish and less fluid, for which reasons the amount of copper used in the new alloyv should not be large. It

is the said-white metal when molten, in addition to securing the very desirable results of preventing grain growth and inter-crystalline corrosion in castings made from the new alloy. I

As is well known, there is no way of predicting the characteristics with any accuracy, of alloys of the kind under consideration, before the alloys are made and tested, as a result of which the eutectic proportions of the constituents of said alloys can only be determined by trial. With a four-element alloy, the number of possible different proportions is so vast that complete experimentation to determine the eutectic proportions is practically prohibitive. When, however, as in the present case, the desirable characteristics of such an alloy are observed to improve with proportions producing a decrease in its melting temperature, and to decrease with proportions producing an increase in its melting temperature, the variation in said-characteristics for different proportions affords a reliable indication as to what the eutectic proportions may be.

In the present case, relatively to said white metal, increased fluidity and increased strength are desired accompanied by elimination of grain growth and inter-crystalline corrosion. Many tests were made with different proportions of the constitutents. With some proportions it was observed that the strength was increased with a decrease in fluidity, and with other proportions that the fluidity was increased with a decrease in strength. With still other proportions and particularly with substantially the preferred proportions above described, it was found that both the fluidity and strength were markedly increased free from grain growth and inter-crystalline corrosion. In view of this, I regard the said preferred proportions of the constituents of the alloy of the invention, as substantially the eutectic proportions of said constituents for the purposes described.

In this connection, however, I desire to point out that the said valuable and desirable characteristics of the improved alloy are realized to a high degree for departures from the said preferred proportions in the ranges above described.

While I have described my invention in the above embodiment, I do not limit myself thereto, as I may; employ equivalents thereof without de parting from thescope of the appended claims.

Having thus described my invention, what I claim is? 1. An alloy for making castings including zinc, aluminum, copper and silicon in substantially the proportions by weight of 91.8% of zinc, 6% of aluminum, 2% of copper and 2% of silicon.

2. An alloy for making castings including substantially 5.5% to 6.5% of aluminum, substantially l to 3% of copper, substantially 0.15% to 0.25% of silicon and zinc to constitute the remaining percentage of the alloy.

JOHN P. GERHAUSER.