FR2504154A1 - PROCESS FOR REFINING HYPEREUTECTICAL ALUMINUM SILICON PRIMARY SILICON - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR REFINING THE PRIMARY SILICON OF HYPEREUTECTIC ALUMINUM-SILICON ALLOYS. IT IS CHARACTERIZED BY PRE-REFINING BY MEANS OF A PHOSPHORUS-BASED PRODUCT FOLLOWED BY MAGNESIUM REFINING IMMEDIATELY BEFORE CASTING. IT FINDS ITS APPLICATION IN THE MANUFACTURING OF LINERS FOR INTERNAL COMBUSTION ENGINES OR ANY OTHER PART SUBJECT TO FRICTION.

Description

-1 PROCESS FOR REFINING SILICIU ML PRIMARY ALUMINUM-SILICON HYPEPR

  The present invention relates to a method for refining primary silicon of hypereutectic aluminum-silicon alloys. The person skilled in the art knows that we classify aluminum-silicon alloys

  in three groups according to their content of additive element

  Those containing about 12.5% by weight of Si are said to be eutectic; those who contain less than or greater than

  value are respectively hypo or hypereutectic.

  In the present case, only hypereutectious alloys are considered

  which, in their elaboration, give successively

  cold, a solid phase containing mainly crystals

  primary silicon then aluminum-silicon eutectic.

  Such alloys trowuvent their application in particular during the manufacture by molding of shirts of internal combustion engines, because such a structure of hard primary silicon crystals embedded in a softer eutectic matrix is particularly suitable for

  to form a surface with microporosities favorable to the re-

  Lubricants and Rubbing Behavior However, it is necessary, however, to obtain suitable results, that these crystals

  have dimensions not exceeding 100 minutes.

  However, this requirement is difficult to respect on the founding parts.

  especially when they are large.

  Therefore, it is necessary, during the development of these alloys, to add elements or compounds called "refining" which multiply

  in the liquid metal the number of centers of germination and

  during cooling, to the formation of small crystals

your dimensions.

  Numerous refining agents have been described in the literature.

  However, we can not use them indifferently because each one of them -2-

has a specific effect.

  If some have an action on silicon crystals

  others, on the contrary, act only on the crystals of

  It is the same that can cause a magnification of the crystals of one of the phases at the same time as they refine

the crystals of the other.

  S. CIIU, in his article "The effect of various elements on the modi-

  fication of Al-Si Alloys "published in the magazine METALLKUNDE n 57 of? Mi

  1966, showed the specificity of these elements and, in particular, in the

  on page 399, he gives a list of elements with their concen-

  which are likely to refine the primary silicon crystals

  mayor ;, Chromium, molybdenum, manganese, tungsten, phosphorus, sulfur, iodine, copper, silver, zinc, tin,

  lead, nickel, cadmium, mercury.

  It can also be read in this article on page 396, in Table 2, that magnesium added to a hypereutectic alloy, unlike all the elements mentioned above, has the effect of swelling the crystals.

  primary silicon and refining the eutectic crystals.

  However, the applicant, in a detailed study of the refining of

  hypereutectic bonds, particularly by phosphorus, was surprised to discover that adding magnesium to such refined alloys did not have the effect of reducing this refining, but, on the contrary,

  the amplified; which goes against the teaching given by (MIU.

  In addition, she noticed that the complementary refining action was fleeting, that is to say that it disappeared gradually over time and that it was therefore necessary to add this magnesium shortly before casting

  to get the most out of its effect.

  Thus, the present invention relates to a process for refining primary silicon of hypereutectic aluminum-silicon alloys

  pre-ripening with a phosphorus product, which is

  by adding a magnesium-based product to this alloy.

4 C 54

-3-

  immediately before pouring it The alloy is prepared in such a way

  re classical and refined by adding 50 to 1000 ppm of phosphorus or a

  corresponding quantity of one of its derivatives, we add to it

  Gnesium The latter may be in the elemental state or aluminum-magnesium parent alloys and in the form of turnings, powder or even

  massive pieces of dimensions compatible with a speed of dissolu-

sufficiently large.

  The quantity used is such that it makes it possible to achieve, in the alli-

  final age, a magnesium content of 500 ppm but, in the case of

  alloying magnesium alloys in their composition,

  can add the amount needed to achieve the desired content.

  The addition is made at a time as close as possible to that of the pouring and in all cases, less than 30 minutes before solidification, because, beyond this lapse of time, the ripening effect fades and becomes practically zero Preferably, the addition is less than five minutes

  before casting to be in optimum ripening conditions.

  It is thus possible to obtain a reduction by about half the size of the primary silicon crystals compared to that obtained in

presence of phosphorus only.

  It is also possible, for a desired crystal size, to reduce the amount of phosphorus required for such refining and to compensate for it by

  a quantity of magnesium Cel has the advantage of reducing the consumption of

  this metalloid and to reduce the quantities present in the

ovens.

  The invention can be illustrated by means of the following examples

EXAMPLE 1

  From a metal bath of A 517 ultra pure, containing a few

  ppm of phosphorus, and at a temperature of 7650 C,

  a sample which has solidified in 13 seconds.

  was, at the examination, primary silicon crystals of medium size

close to 50 Vm.

C 4 1 54

  0.1% of magnesium was then added to the same bath and then, two minutes after the introduction, the samples were taken, solidified and examined in the same

  conditions than previously, a new sample: the size of

  The same operations were repeated one hour after the introduction of magnesium and then led to the observation of crystals of 40 μm, thus showing the fugacity of the effect.

of this refining element.

EXAMPLE 2

  A metal bath of A 517 has been divided into three separate volumes

  added to each of the different amounts of phosphorus,

  between 10 and 50 ppm Each of them was sampled

  solidified in thirteen seconds and the structure of which was examined

  ture: the size of the primary silicon crystals observed was:

40 60 pm.

  At each volume, 0.1% Mg was added and, two minutes after introduction,

  of this element, the same operations were carried out as those performed on the non-magnesium-treated alloy.

  grains was respectively, for each of the samples: 11 19 -

32 rn.

  It can be seen that magnesium has the effect of dividing the size of

  primary silicon grains by a factor of about 2.

EXAMPLE 3

  From a bath of A 517 U 4 C, at a temperature of 780 C, to which was added cuprophosphorus at 15% of phosphorus, so as to reach a phosphorus content of 700 ppm, a certain amount was taken. of liquid to cast it in the form of tensile test pieces After solidification, the size of the primary silicon crystals observed

  these specimens exceeded 50 minutes.

  In the remaining bath, 0.6% magnesium was added and the medium was immersed immediately.

  after the introduction and fusion of the latter, other test pieces; these had, after solidification, a grain size of

  Thus confirming the role of magnesium as a refining element.

-

  The present invention finds application in the refining of alloys

  hypereutectic aluminum alloys and is of great interest,

  when these alloys are intended for the manufacture of

  internal combustion engines or any other parts subject to rubbing

clothes.

Claims (3)

  1 / Process for refining primary silicon of aluminum alloys   hypereutectic silicon in which is carried out a pre-refining with a product based on phosphorus, characterized in that one adds to this alloy a magnesium-based product imnédiatement immediately before casting. 2 / A method according to claim 1, characterized in that the product   magnesium-based is added less than thirty minutes before casting.   3 / A method according to claim 1, characterized in that the quantity   added magnesium product is such that it allows   dyeing, in the final alloy, a magnesium content of 500 O ppm less.