FR2875817A1 - Extruded rod used in the production of a forged piston in combustion engines is made from an aluminum alloy containing alloying additions of silicon, copper, magnesium, chromium, nickel and titanium - Google Patents

Abstract

Extruded rod is made from an aluminum alloy containing (in wt.%): 10.5-11.8 Si, 3.3-4.0 Cu, 0.4-0.7 Mg, 0.05-0.20 Cr, 0.28-0.42 Ni, 0.03-0.1 Ti, 0-0.05 Zn, 0-0.05 Mn, 0-0.30 Fe and a balance of aluminum. The alloy optionally contains 0.01-0.03 Sr.

Description

Forged aluminum alloy piston Field of the invention

  The invention relates to a forged aluminum alloy piston type AI-SiCu with high fatigue resistance, especially for use in internal combustion engines.

  STATE OF THE ART In internal combustion engines, pistons molded aluminum alloy type Al-Si are commonly used. These alloys are resistant to abrasion, thermal and mechanical stresses, and fatigue in a temperature range typically between -20 C and 400 C.

  DE 198 29 047 A1 (Aisin Seiki KK) discloses a molded piston alloy of composition Si 13 16 Cu 2 5 Mg 0.2 1.3 Ni 1.0 2.5 V 0.05 0.2 P 0.004 0.02.

  If 11.0 14.0 Cu 5.6 8.0 Mg 0.5 1.5 Ni 0.05 0.9 Mn0 1.0 Ti0.05 1, 2 Zr0.12 1.2 Zn0.05 0.9 Fe 0 0.8 Sr 0.001 0.1.

  For the same application, patent application DE 198 45 279 A1 (Alcan Deutschland GmbH) offers alloys of Al-Si type with a much higher nickel content, up to 12%.

  Forged pistons are also known, which generally have better fatigue strength than molded pistons. Patent EP 924 310 B1 (Federal Mogul) proposes for this purpose an alloy of composition US Pat. No. 6,399,020 (United States of America) discloses a molded piston alloy of composition Si 10.5 13.5 Cu 2.0 4.0 Mg 0.81 1.5 Ni 0.5 2.0 Co 0.3 0.9 P> 20 ppm Ti 0.05 0.2 or (Zr and / or V 0 0.2).

  Cobalt leads to the formation of small intermetallic phases, which act favorably on the heat resistance of the alloy.

  UK Patent Application 2,300,198 A (British Aluminum Holdings Ltd) discloses a forged piston alloy of composition Si 10.5 12.5 Cu 2.8 4.0 Mg 1.1 1.8 Ni 1.0 1, 8 Fe 0.3 1.0 Mn 0 0.5 B, V, Zn, Cr, Ti 0 0.2 each and <0.5 in total.

  EP 790 325 B1 (Corus) discloses spun products of composition Si 11.0 13.5 Cu 0 0.35 Mg 0.5 2.0 Mn 0 1.2 Ni, Zr, Cr, Zn 0 0.1 each Fe, Bi, Pb, Sn 0 1.0 each Sr 0.02 0.1.

  This patent proposes the use of this alloy for the manufacture of spun components for hydraulic and pneumatic systems, at temperatures not exceeding 150 C.

  Patent Application WO 03/010429 (Showa Denko KK) discloses a piston forged from a molded part for an internal combustion engine manufactured using an aluminum alloy containing 6 to 25% by weight of silicon and including a skirt and an annular groove for the oil.

  US Pat. No. 5,993,576 (Furukawa Electric Co) discloses an abrasion-resistant wrought alloy of composition Si 10 12 Cu 2 4 Mg 0.5 1, 2 Ni 0.2 0.3 Fe 0.1 0.5 Cr 0, 0.3 0.3 and at least one of Sr 0.01 0.03 Sb 0.05 0.3 the remaining Mn content such that Mn <0.04 US Pat. No. 5,123,973 (Alcoa) discloses an extruded bar of composition If 11 13.5 Cu 0.5 1.45 Mg 0.8 3 Ni 0.5 2.95 the contents of Fe, Cr and Zn are respectively less than 1, 0.1 and 0.25 The problem that this The invention proposes to solve is to provide an aluminum alloy piston which has improved fatigue resistance.

Description of figures

  FIG. 1 shows the fatigue strength of alloys A (symbol: black filled diamond) and B (symbol: square not filled), measured on cylindrical test pieces during a fatigue test in axial stress with R = 0, 1.

Description of the invention

  (a) Definitions Unless otherwise stated, all information relating to the chemical composition of alloys is expressed in percent by mass. Therefore, in a mathematical expression, 0.4 Zn means: 0.4 times the zinc content, expressed in percent by weight; this applies mutatis mutandis to other chemical elements. The designation of the alloys follows the rules of The Aluminum Association, known to those skilled in the art. The metallurgical states are defined in the European standard EN 515. The chemical composition of standardized aluminum alloys is defined for example in the standard EN 573-3. Unless otherwise stated, the static mechanical characteristics, ie the breaking strength Rm, the yield strength Rpo, 2, and the elongation at break A, are determined by a tensile test according to EN 10002-1, the location and direction of sample collection being defined in EN 755-1 and EN 754-1. Fatigue strength is determined by a test according to ASTM E 466. The term spun product includes so-called stretched products, i.e., products that are made by spinning followed by drawing.

  Unless otherwise stated, the definitions of the European standard EN 12258-1 apply.

  b) Detailed description of the invention

  The present invention can be applied to wrought aluminum alloys, that is to say aluminum-based alloys intended to be processed in particular by techniques such as rolling, spinning, stamping, forging, such as Al-Si (series 4xxx) containing between 8 and 14% of silicon, and preferably between 10.5 and 13.0% of silicon, between 0.6 and 4.0% of copper, between 0.4 and 1.3 % magnesium, and between 0, 25 and 1.3% nickel. The alloy may also contain titanium (0.02 0.05%), strontium (0.01 0.03%), chromium (at most 0.20%), and, as impurities, iron (not more than 0.50%), manganese (not more than 0.10%) and zinc (not more than 0.10%). A composition in which Fe + Mn + Ti does not exceed 0.60% is preferred.

  Copper leads to the structural hardening of the alloy. Magnesium contributes to the hardening of the alloy. Nickel contributes to the stability of the alloy at high temperatures. Titanium and chromium elements refine the grain.

  Strontium contributes to modifying the structure, in particular the silicon particles in such an alloy.

  In a particularly preferred embodiment, the alloy has the following composition: Si 10.5 11.8 and preferentially 10.6 11.7 Cu 3.3 4.0 Mg 0.4 0.7 and preferably 0.45 0.65 Cr 0.05 0.20 and preferentially 0.10 0.14 Ni 0.28 0.42 Ti 0.03 0.1 and preferably 0.03 0.05 Zn 0 0.05 Sr 0.01 0 , 03 Mn 0 0.05 Fe 0 0.50 and preferably 0 0.30 Fe + Mn + Ti <0.60 and preferentially Fe + Mn + Ti 0.40 other elements at most 0.05 each and at most 0, 15 in total.

  In a particularly advantageous embodiment, the Ni content is between 0.32 and 0.42.

  The alloy is typically cast into spinning billets according to known techniques, homogenized, hot-spun into bars, and optionally quenched on a press. Reverse spinning is preferred which leads to a more even microstructure along the bar. Spun bars are cut into forging blanks of appropriate size. The forging is typically at a temperature between 400 C and 480 C. It is followed by quenching. Forged parts are put in solution, typically at a temperature between 460 C and 530 C, and quenched. Subsequently, they undergo a tempering treatment at a temperature of between 150 ° C. and 180 ° C., and preferably between 160 ° C. and 170 ° C. In an advantageous embodiment of the invention, the dissolution operation is not carried out and quenching is carried out directly after the forging, made at a temperature between 400 and 480 C. The quenching after forging is followed by a tempering at a temperature between 150 C and 180 C and preferably between 160 and 170 C.

  The forged piston according to the invention is particularly suitable for use in an internal combustion engine of a vehicle, and in particular a racing car, which must have the highest possible performance for a very short time of use. order of dozens of hours, or even only a few hours, but whose longevity is not a particularly important criterion in this context. By way of example, the piston according to the invention can be used in an internal combustion engine for a Formula 1 racing car. The concept of Formula 1 refers to a particular competition regulation, and involves the use of race cars specifically adapted to this competition. More particularly, an internal combustion engine for a Formula 1 racing car is typically subjected to maximum demand for the duration of a few competitions (and of the order of a few hours), and then subjected to intensive technical verification, during which can replace worn parts. The maximum permissible stress for a limited time is an important criterion for these applications as a result, the longevity of the piston is not a particularly important criterion in this context, unlike passenger vehicles intended for use on public road network. The forged piston according to the invention can have a fatigue strength greater than 106 cycles (R = 0.1) for a stress of 300 MPa; a piston forged with the composition Si 10.6 11.7 Cu 3.3 4.0 Mg 0.45 0.65 Cr 0.10 0.14 Ni 0.32 0.42 Ti 0.03 0.05 Zn 0 0.05. Mn 0 0.05 Fe 0 0.30 holds even more than 106 cycles (R = 0.1) at a stress of 350 MPa. The forged piston according to the invention can also be used in other racing vehicles, in particular in cars, motorcycles or racing ships. The piston according to the invention can also be used in vehicles intended for the general public as well as in commercial vehicles and any other vehicle using an internal combustion engine. It can also be used in hydraulic or pneumatic installations, especially at elevated temperatures.

  In the examples which follow, advantageous embodiments of the invention are illustrated by way of illustration. These examples are not limiting in nature.

Examples:

  Two cylindrical bars were spin-spinned by spinning from two alloys A and B, the approximate chemical composition of which is shown in Table 1.

Table 1

  If Cu Mg Cr Ni Ti Sr Fe + Mn + Ti A 11.2 3.65 0.55 0.12 0.35 0.04 0.02 <0.40 B 11.8 1.0 1.0 1, 0 0.60 Their mechanical characteristics in the L sense (long direction) are collated in Table 2. Ag is the distributed elongation (in English: uniform elongation), and n is the coefficient of hardening (in English: hardening exponent). .

Table 2

  Ambient temperature 150 C reached in 30 min Rp0.2 R ,,, Ag A n Rp0.2 R ,,, A [%] [MPa] [MPa] [%] [%] (2-20%) [MPa] [MPa] A 355 443 7.49 0.074 318 362 11, 5 B 311 377 7.3 10.9 0.071 268 312 14.0 Fatigue strength was also determined by an axial stress test with R = 0.1 at room temperature on cylindrical samples with a smooth surface. The results are given in Table 3 and Figure 1.

Table 3

  Alloy Stress [MPa] Number of cycles A 300 10 803 100 (*) A 300 12 495 400 (*) A 360 2 784 400 A 420 26 900 A 400 29 500 A 380 61 500 A 3 70 1 13 5 200 A 360 130 900 (**) A 350 2 041 500 A 350 4 117 800 A 360 2 174 400 A 370 2 444 300 A '360 1 956 000 A 350 6 337 700 A 340 6 670 000 A 380 746 800 A 330 10768000 A 400 165 700 B 340 77 600 B 340 122 700 B 300 13 055 100 (*) B 320 142 600 B 320 87 100 B 300 1 146 100 B 300 10 803 100 (*) test piece not broken (**) initiation of rupture on surface defect For sample A, micrographs after anodic attack show a recrystallization with fairly fine grains (diameter about 50 m to 100 m).

  From these bars, cylindrical pistons were forged. The forging operation was carried out at 460 C. A dissolution at a temperature of 500 C and an income of 10h at 165 C were then performed on the pistons. The pistons were finished by machining.

Claims (9)

  1. Spun bar made of aluminum alloy for the production of forgings of weight composition: Si 10.5 11.8 Cu 3.3 4.0 Mg 0.4 0.7 Cr 0.05 0.20 Ni 0.28 0.42 Ti 0.03 0.1 Zn 0 0.05. Mn 0 0, 05 Fe 0 0.30 Other elements 0.05 each and 0.15 in total, the rest aluminum, said alloy 10 possibly containing Sr 0.01-0.03 2. Spun bar according to claim 1 characterized in that Si 10.6 11.7 Mg 0.45 0.65 Cr 0.10 0.14 Ti 0.03 0.05 3. Spun bar according to claim 2, characterized in that Ni 0.32-0.42 4. Forged piston characterized in that it has been forged from a bar spun according to any one of claims 1 to 3.   Forged piston according to claim 4, characterized in that it has been forged at a temperature of between 400 ° C. and 480 ° C. and then treated with a sequence of steps comprising dissolving at a temperature of between 4 ° C. and 4 ° C. 530 C, quenching after dissolution, and income.   6. Forged piston according to claim 4 characterized in that it was forged at a temperature between 400 C and 480 C, and then treated with a sequence of steps including quenching after forging and income.   7. Forged piston according to claim 5 or 6, characterized in that the tempering temperature is between 160 and 170 C.   8. Use of a piston according to any one of claims 4 to 7 in a vehicle internal combustion engine.   9. Use of a piston according to any one of claims 4 to 7 in a Formula 1 racing car engine.