US3032412A - Nondisintegrating alloy - Google Patents

Description

Unite rates 3,032,412 NONDISINTEGRATHNG ALLOY Robert W. Freeman, St. Catherines, Ontario, Canada, as-

signor to Union Carbide Corporation, a corporation of New York No Drawing. Filed Apr. 8, 1960, Ser. No. 2%),340 4 Claims. (Cl. 75-438) This invention relates to an addition agent for refining aluminum alloys and, in particular, to a phosphorusbearing silicon-base addition agent.

It is common practice in the aluminum industry to use small amounts of various addition agents for the purpose of improving the structure of aluminum alloy castings. Heavy-sectioned castings show a marked improvement in properties as a result of the finer grain structure afforded by the use of modifiers for example.

Another suggested procedure involves the addition of phosphorus which is known to function effectively in hypereutectic aluminum-silicon alloys as a nucleating agent for refinement of the primary silicon phase during the precipitation of this phase.

A commercially acceptable means for providing for an addition of phosphorus is needed, however. Alloy addition agents consisting of phosphorus and copper are used but are not always suitable because the copper addition is sometimes detrimental to the finished casting. Addition agents composed of phosphorus and silicon, a seemingly useful combination for use with-aluminum-silicon alloys, have been suggested but have heretofore been unacceptable for general foundry use because of the tendency of a silicon-phosphorus alloy to disintegrate during storage.

The disintegration of such silicon-phosphorus alloys is not due to the mere crumbling of a brittle material, but rather is a spontaneous crumbling or disintegration of a previously sound silicon-phosphorus alloy upon standing. The tendency to disintegrate is accelerated by excessive moisture conditions.

The disintegration of these silicon-phosphorus alloys is detrimental in that such materials are not suitable for use in present-day foundry practice; and also because the disintegration of the alloy liberates potentially dangerous phosphine gas.

It is the primary object of this invention, therefore, to provide a nondisintegrating silicon-phosphorus alloy.

It is also the object of this invention to provide a stable, nondisintegrating silicon-phosphorus alloy for use as a refining agent for alumnium alloys.

Other aims and advantages of this invention will be apparent from the following description and the appended claims.

In accordance with these objects a silicon-phosphorus alloy is provided consisting essentially of a maximum of 1 percent by weight phosphorus, less than 0.1 percent by weight aluminum, and the balance substantially all silicon and incidental impurities.

The alloy should preferably contain less than 0.13 percent by weight in the aggregate of aluminum and calcium even when the aluminum content is less than 0.1 percent. Furthermore, the alloy should preferably not contain more than 2 percent by weight iron since iron contents higher than this are often detrimental to the finished casting.

The silicon-phosphorus alloy of this invention is seen to contain certain maximum allowable amounts of the SfifiZAlZ Patented May 1, 19%.?

elements phosphorus, aluminum, calcium, and iron. The limit set on these materials is made in view of the discovery that the disintegration of silicon-phosphorus alloys as currently produced was due to the chemical union of aluminum and/ or calcium impurities with phosphorus. When alloys are produced in accordance with this invention, wherein the stated materials are present only in the indicated amounts, the alloys produced will be stable and nondisintegrating.

Aluminum and calcium are found in these siliconphosphorus alloys because aluminum and calcium are contained in the silicon metal used in producing the alloy. Iron contents result from the use of ferrophosphorus to supply the phosphorus addition. By using silicon metal having low aluminum and calcium contents, alloys can be produced within the indicated ranges.

It is believed that the actual mechanism of disintegration involves the formation of phosphides of aluminum and calcium in silicon-phosphorus alloys when these materials are present as impurities in certain amounts. These phosphides are extremely hygroscopic and, when exposed to a humid atmosphere, decompose to a white substance and evolve a gas that is believed to be primarily phosphine. The decomposition reaction can be microscopically observed to result in the expansion of a unit area containing the phosphide. The pressures generated by this expansion cause the formation of cracks, and the eventual disintegration of the alloy.

Specific amounts of these materials are required before disintegration takes placer Aluminumis a very strong inducer of disintegration and so aluminum contents are always kept below 0.1 percent. Calcium also induces disintegration and it has been found that the aggregate of aluminum and calcium is preferably kept below 0.13 percent. Therefore, even if less than 0.1 percent aluminum is present, the calcium content should be low enough to keep the aggregate amount of aluminum and calcium below 0.13 percent. The phosphorus content is preferably limited to 1 percent and may be varied safely up to this amount provided the aluminum and calcium contents are kept below the indicated maximums. Phosphorus contents of 0.5 percent have been found adequate for most foundry uses.

It has also been found that the rate of cooling of these alloys affects the tendency to disintegrate. The slow cooled specimens have a greater tendency to disintegrate into powdery material than chilled or rapidly cooled specimens which tend to disintegrate into chunks with a lesser amount of powder. Specimens of heretofore produced silicon-phosphorus alloys, whether slow cooled or rapid cooled, still show objectionable amounts of disintegration, however.

Tests were conducted wherein the nondisintegrating nature of the alloys of this invention are shown in comparison to alloys in which aluminum contents and calcium contents are not regulated. In Table I the results of studies made on several specimens of silicon-phosphorus alloys containing over 0.1 percent aluminum and some calcium are shown. The balance of the alloys is silicon. These alloys all disintegrated to a greater or lesser degree. Those alloys containing relatively large aggregate amounts of aluminum and calcium, such as alloys 7 and 8, exhibit severe disintegration. It is also seen that the slow-cooled specimens are more subject to disintegration than rapidly cooled specimens.

TABLE I Dismtegratmg Alloys Percent Alloy No. Method of Amount of Disin- Cooling tegration P Ca Al 1 0.42 0.02 0.26 Chilled h'Ioderate-to-heavydisintegration to chunks. 2 0.42 0.02 0.26 Slow-eeoled Moderate to fine disintegration to fine material. 3' 0.46 0.04 0.32 Chilled Heavy disintegration to chunks. 4'. 0.46 0.04 0.32 Slow-cooled. l ioderate-to-heavydisintegration to fine material. 5; 0. 40 0.004 0.26 Chilled Slight amount of disintegration to chunks. 6 0.40 0.004 0.26 Slow-cooled- Moderate-to-heavydisintegration to fine material. 7 0.45 0.08 0.18 Chilled Heavy, 75% disiutegration to chunks. S 0.45 0.08 0.18 Slow-cooled Heavy, 90% disintegration to line material.

In Table II several specimens of alloys made according to this invention are shown. These alloys were produced fromsilicon metal containing low aluminum and calcium contents and ferrophosphorus containing 26 percent phosphorus metal. These alloys are prepared by melting the silicon and adding the ferrophosphorus. The iron-content of these alloys is not shown but was less thanZ percent and the balance is silicon. All of these alloys contain less than 0.1 percent aluminum and are able to contain relatively large amounts of phosphorus without any disintegration. The method of cooling does not afiec't the alloy. Slow cooled specimens do not disintegrate more severely than chilled alloys as did ordinary silicon-phosphorus alloys. However, a rapidly cooled or chilled alloy is preferable over a slow cooled material to minimize any possibility of disintegration.

TABLE II N ondisintegrating- Alloys A'lloyNo. P Ca A1 Method of Amount of Cooling Disintegration 0.29 0. 01 0. 042 Chilled N o disintegration. 0. 29 0. 01 0. 042 Slow-cooled Do. 0.51 0. 01 0. 042 Chilled Do. 0. 51 0. 01 0. 042 Slow-cooled. Do. 0. 60 0. 016 0. 028 Chilled D0. 0. 00 0. 016 0. 028 Slow-coolecL Do. 0. 94 0. 01 0. 068 Chilled Do. 0. 94 0. 01 0. 068 Slow-cooled- Do. 0. 54 0. 04 0. 043 Chilled D0. 0. 54 0. 04 0. 043 S1owcooled Do. 0. 59 0 04 0. 051 Chilled D0. 0. 59 0. 04 0. 051 Slow-cooled- Do.

Several of these alloys were placed in a wet desiccator for disintegration tests. Even after extended periods of time no disintegration occurred as is the case when alloys having high aluminum contents are similarly tested.

It is apparent, therefore, thatv these low-aluminum silicon-phosphorus alloys are suitable for foundry use, possessing great stability in severe transit and storage conditions, the alloys constitute a useful contribution to the metallurgical field.

The description of the invention above has been in terms of its specific embodiments. Modifications and equivalents will be apparent to those skilled in the art and this disclosure is intended to be illustrative of, but not necessarily to constitute a limitation upon, the scope of the invention.

What is claimed is:

1. A nondisintegrating silicon-phosphorus alloy consisting essentially of from about 0.3 to '1 percent by weight phosphorus, less than 0.1 percent by weight aluminum, and the balance substantially all silicon and incidental impurities.

2. A nondisintegrating silicon-phosphorus alloy consisting essentially of from about 0.3 to 1 percent by weight phosphorus, less than 0.1 percent by weight aluminum, less than 0.13 percent by weight in the aggregate of calcium and aluminum Whencalcium is present in the alloy, less than 2 percentby Weight iron, and the balance substantially all silicon and incidental impurities.

3. A nondisintegrating silicon-phosphorus alloy cohsisting essentially of about 0.5 percent by weight phosphorus, less thanill percent aluminum, less than 2 percent by weight iron, and the balance substantially all silicon andincidental impurities.

4. A nondisintegrating silicon-phosphorus alloy consisting essentially of about 0.5 percent by weight phosphorus, less than 0.1 percent by weight aluminum, less than 0.13 percent by "weight in the aggregate of calcium and aluminum when calcium is present in the alloy, less than 2 percent by weight iron, and the balance substantially all silicon and incidental'impuritie's.

2,402,839 Ohl June-2s, 1946

Claims (1)

1. A NONDISINTEGRATING SILICON-PHOSPHORUS ALLOY CONSISTING ESSENTIALLY OF FROM ABOUT 0.3 TO 1 PERCENT BY WEIGHT PHOSPHORUS, LESS THAN 0.1 PERCENT BY WEIGHT ALUMINUM, AND THE BALANCE SUBSTANTIALLY ALL SILICON AND INCIDENTAL IMPURITIES.