Alloys or metallic compositions – Aluminum base
Patent
1984-06-04
1986-06-17
Brody, Christopher W.
Alloys or metallic compositions
Aluminum base
420590, 75 68R, C22C 110, C22C 2100
Patent
active
045955590
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the production of composite alloys based on aluminum, which may or may not be alloyed, and boron, and application thereof.
It is general practice among those involved in the melting and casing of aluminum to add boron to the molten metal to cause the production of TiB.sub.2 crystals which play an important part in regard to seeding of the Al crystals upon solidification and which constitute an excellent way of refining the grain size upon casting.
It is also known for aluminum alloys to be doped with that element in order to precipitate titanium in the form of TiB.sub.2 crystals, thereby to enhance their electrical conductivity.
In such uses, boron is added to the aluminum at relatively low levels of concentration, which are in the range of a few hundreds of ppm, and, if the introduction of such small amounts gave rise to problems at a certain period of time, that has been overcome since then by virtue of using mother alloys such as AT5B. The situation is not the same when the levels of concentration of boron to be attained are of the order of several percent.
It is known in fact that the solubility of boron in aluminum is very low and is on the order of 300 ppm at the melting point of aluminum, so that, if the attempt is made to produce boron-charged alloys using the conventional process of melting and casting in the form of ingots, difficulties are encountered due to incomplete dissolution, substantial losses of boron, and a severe degree of segregation of the boron. The effect of that is to result in composite alloys which overall do not comply with the compositions expected and which are of a heterogeneous structure.
It is for that reason that research workers and companies have sought to remedy such disadvantages, and have proposed various solutions of greater or lesser attractiveness.
In French Pat. No. 1,265,089 concerning an aluminum alloy containing from 2.5 to 10% of boron, the inventor recalls that hitherto it had been necessary to prepare such alloys either by adding boron to molten aluminum or by reducing a boron compound such as borax, with the molten aluminum. However, in the former case, the alloys contained only a very small amount of boron in alloy form and required excessively long periods of dissolution, while in the latter case the use of borax resulted in occlusions of undesirable nature of oxygen and other impurities. The inventor then proposes incorporating the boron by the reduction of an alkali metal fluoborate in contact with the molten aluminum. However, it should be noted that such a process, besides the burdensome installation that it requires for the process to be carried into effect, results in poor yields, a part of the boron being lost both in the form of KBF.sub.4 and BF.sub.3, which is a highly toxic compound by virtue of the emissions of HF to which it gives rise in a humid atmosphere.
Moreover, the alloy produced in that way serves as a mother alloy for the refining of aluminum, that is to say, a very small amount thereof is introduced into the bath to be refined and consequently the problem of its homogeneity is not a matter of substantial importance, as what counts above all is a mean concentration of boron in the bath.
The problem becomes more severe when alloys with a high boron content are intended for example for the production of components which must have either a high level of resistance to abrasion or a suitable capacity for absorbing neutron radiation, as in that case the boron must be regularly distributed so that it is capable of performing its function in a uniform fashion throughout the component.
Thus, the solutions which have been proposed hitherto move away from the process of producing mother alloys and are oriented rather towards powder metallurgy. Thus, French patent No. 2,231,764 claims a process for the production of metal boron-containing products which are intended for the nuclear industry, characterized in that the metal material and the boron-base substance are in the form of powders, said powder
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Brody Christopher W.
Fonderies Montupet
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