Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Metal and nonmetal in final product
Patent
1984-02-13
1987-03-17
Lechert, Jr., Stephen J.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Metal and nonmetal in final product
123193C, 419 23, 420548, B22F 706, F02F 7506
Patent
active
046506446
DESCRIPTION:
BRIEF SUMMARY
This invention relates to liners of internal combustion engines whose structure exhibits silicon grains that are graded in size and dispersed in a eutetic aluminum-silicon alloy matrix. It also relates to some of the processes for obtaining them.
Engine liners having an aluminum base are not new but their use has always caused problems of compatibility of their working surfaces with the engine elements such as the pistons that are in contact with them. Efforts have been made in various ways to reduce the difficulties encountered such as providing a steel lining, coating the surface of the cylinder bore with harder metals such as iron or chromium, without, however, being able to overcome the difficulties completely.
Then alloys were used having a better mechanical resistance such as hypereutectic aluminum-silicons but it was noticed that the primary silicon crystals that appeared during casting of the liner had, because of their relatively large size and their angular shape, a troublesome tendency to score the surface of the pistons and this led to protecting the piston surface with a covering.
Then, still desiring to benefit from certain advantages offered by the hypereutectic aluminum-silicons, an effort was made to change the structure of these alloys, particularly at the level of the silicon grains to try to give them the necessary compatibility without having to resort to further surface treatments. Of the attempts made, there can be noted aluminum matrix was used to bring in relief the silicon grains then these grains were polished and, is the case of French Pat. No. 2 235 534 in which the liner is cast under such cooling conditions so that it does not exhibit any primary silicon phase but rather fibrous or spheroidized particles with dimensions less than 10 .mu.m.
More recently, the applicant in Pat. No. 2 343 895 also resorted to new hypereutectic A-S structures but by substituting the casting process with that of extrusion of powders obtained by atomization. Actually, this technique offers the advantage of using powders formed at a high cooling speed and in which the primary silicon grains have a relatively small size and in any case one that is smaller than that resulting from conventional casting. This size is not modified by the extrusion and thus a new structure is obtained exhibiting fine, well distributed silicon particles that notably improve the compatibility of the liner with the piston.
However, under particularly severe test conditions, a deterioration of the liner was still observed.
A thorough study of the phenomenon found that it was linked with too great a fineness of the silicon grains. Starting with these results, the present inventors realized that it was possible to improve this compatability. For this reason, the present inventors have developed liners whose structure exhibits silicon grains carefully graded in size in a relative narrow granulometry, on an average being above the maximum that led to a poor performance and below the one that was too coarse for the cast products.
This invention therefore relates to an internal combustion engine liner having a eutectic aluminum-silicon alloy base, optionally containing other elements and characterized in that its structure exhibits a distribution of silicon grains graded in size with dimensions between 20 and 50 .mu.m.
Thus, this liner consists of a eutectic aluminum-silicon matrix, i.e., containing about 12% of silicon and in which no primary silicon grain appears. Optionally, this alloy can contain other additional elements which contribute to its mechanical characteristics or certain properties in relation to friction or wear behavior.
In this matrix are distributed silicon grains that are graded in size, i.e., responding to the narrowest possible granulometry curve whose dimensions in any case are between 20 and 50 .mu.m. Thus, all fine silicon particles and grains that are too large which contribute to reducing the desired compatibility are excluded.
Further, to obtain a favorable compromise between the qualities provided, on
REFERENCES:
patent: 2978798 (1961-04-01), Wasserman et al.
patent: 4068645 (1978-01-01), Jenkinson
patent: 4099314 (1978-07-01), Perrot et al.
"New Alloy Cylinder Linings Take Uncoated Pistons", Automtive Engr., Sep. 1977, p. 22.
Huret Noel
Meunier Jean
Aluminium Pechiney
Lechert Jr. Stephen J.
Wallen T. J.
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