Aluminum alloy useful in powder metallurgy process

Abstract: The present invention provides an aluminum alloy consisting essentially of (a) 5 to 30% by weight of Si, (b) 0.5 to 10% by weight of at least one species selected from the group consisting of Fe, Ni, Cr and Mn with the proviso that the total amount of these species cannot exceed 20% by weight, (c) 0.3 to 3% by weight of at least one species selected from the group consisting of Mo, Zr, V and Ti with the proviso that the total amount of these species cannot exceed 5% by weight, and (d) aluminum in a remaining amount. An aluminium alloy product produced by extruding said alloy is excellent in strength at high temperatures and resistance to creep.

Description: The present invention relates to an aluminum alloy which provides a product having a highly improved strength at elevated temperatures and remarkable resistance to creep when used in powder metallurgy process. Products of an aluminum alloy prepared by a powder metallurgy process (hereinafter referred to as "P/M process") exhibit highly improved heat resistance, wear resistance, and like properties in comparison with the products prepared by an ingot metallurgy process (hereinafter referred to as "IM process") because the products by the P/M process can contain additional elements in larger amounts with no segregation and being more uniformly dispersed in the aluminum matrix than the products prepared by the IM process. Conventional P/M aluminum alloy products are usually produced by hot extrusion of a powdery, flaky or ribbon-like quickly solidified material to obtain a billet and processing the billet to the desired shapes or forms. During the hot extrusion step, the oxide films on the surfaces of the powder particles, flakes or ribbons are fractured and the exposed inner aluminum portions are pressed against each other to form strong bonding. In a powder-rolling process and a powder-forging process which also belong to a general category of the P/M process, aluminum oxide films are fractured; however, since the shearing force is relatively small and deformation of each particle is not so large and uniform as in the case of extrusion, the bond between particles is not so strong as in the extruded product. The extrusion ratio in conducting the above extrusion by the P/M process is usually 10 or more, preferably 20 or more to obtain a strong bonding of each particle. The extrusion by the P/M process usually requires much higher forces than the extrusion by the IM process because the aluminum alloy used in the former process contains larger amounts of alloying elements. For these limitations, aluminum alloy materials obtained by the P/M process are difficult to employ for producing large-sized products. Further, aluminum alloys conventionally used in the P/M process give a product which cannot fully meet the severe requirements such as high strengths at elevated temperatures up to 300°C, high resistance to creep, etc. US-A-3325279 relates to aluminum high silicon alloys and discloses an alloy containing 29% Si, 3.6% Fe and 2.7% Ti, with the balance Al. EP-A-0341714 (document in accordance with Article 54(3) EPC) discloses an aluminum alloy containing 25% Si, 3% Fe, 5% Ni and 1% Mo produced by a P/M process and extruded at 450°C at varying extrusion ratios between 3:1 and 20:1. An object of the the invention is to provide a P/M aluminum alloy which can be extruded under a low extrusion ratio of 10 or lower. Another object of the invention is to provide a P/M aluminum alloy which can be extruded even under an extremely low extrusion ratio of 2 to 5. Still another object of the invention is to provide a P/M aluminum alloy capable of producing an extruded product excellent in strength at high temperatures and resistance to creep. These objects are achieved by the aluminum alloy and product according to the claims: Other objects and features of the invention will become apparent from the following description. We conducted extensive research to obviate the prior art problems as mentioned above and found that these problems can be markedly alleviated by use of a powdery aluminum alloy comprising specific alloying elements. The present invention has been accomplished on the basis of this novel finding. When the aluminum alloys of the invention comprising specific components are extruded, the powder particles are strongly bonded to each other even at a low extrusion ratio and the extruded material exhibits substantially uniform strength and elongation irrespective of the extrusion ratio. If an aluminum alloy powder with the composition outside the specified range is used, an extruded material with strong bonding cannot be obtained at a low extrusion ratio of 10 or 5 to 2 at a temperature of 400 to 500°C. Stated more specifically, if the amount of Si is less than 5% by weight of the alloy, the bonding strength of the particles is low; whereas the use of Si of more than 30% by weight results in the excess volume of primary Si particles in the matrix which leads to a reduction in the toughness of the alloy. Fe, Ni, Cr and Mn mainly contribute to the improvement of heat resistance and strength. The amount of at least one of Fe, Ni, Cr and Mn in less than 0.5% by weight results in inferior heat resistance and strength of the extruded material whereas the amount thereof in more than 10% by weight results in lower toughness with the formation of coarse intermetallic compounds. The total amount of these alloying elements in excess of 20% by weight also leads to a reduction of toughness of the alloy. Mo, Zr, V and Ti mainly contribute to the improvement of heat resistance and creep resistance. The amount of at least one of Mo, Zr, V and Ti in less than 0.3% by weight does not significantly improve the resistance to heat and creep. On the other hand, when the amount thereof exceeds 3% by weight, coarse intermetallic compounds are formed to lower the toughness of the alloy. When two or more of Mo, Zr, V and Ti are used, the total amount is up to 5% by weight of the alloy to prevent the formation of coarse intermetallic compounds which lead to reduced toughness. The aluminum alloy of the invention contains 5 to 30% by weight of Si, 2 to 5% by of Fe, 2 to 5% by weight of Ni, 0.5 to 3% by weight of Mo and 0.5 to 3% by weight of Zr provided that the total amount of Mo and Zr is more than 2% by weight and less than 5% by weight. The aluminum alloy of the invention containing alloying elements in the above ranges shows much more balanced properties of the improved strength, toughness and resistance to creep at elevated temperatures. Thus, the aluminum alloys with alloying elements in the above range are most useful as the materials for machine components, etc. When the aluminum alloy of the invention is extruded at a temperature between 400 to 500°C, a very strong bond can be produced in an extruded material at a low extrusion ratio of 10 or less, or even at a very low extrusion ratio of 2 to 5. The extruded product formed from the aluminum alloy of the invention exhibits high resistance to heat and creep. EXAMPLES Given below are Examples to clarify the features of the invention in greater detail. Example 1 Aluminum alloys containing alloying elements as indicated in Table 1 below were air-atomized into particles and sieved to prepare powders by passing through sieve openings of 150µm x 100µm (powders of minus 100 mesh). No. Alloying Elements (wt.%) Si Fe Ni Cr Mn Mo Zr V Ti 1 6 5 3 2 2 12 1 1 1 1 2 3 12 5 3 0.7 4 12 5 3 2 5 12 5 3 2 6 12 5 3 2 7 12 5 3 2 8 17 5 3 1 9 17 5 3 1 10 20 3 3 2 11 20 5 3 1 12 25 4 5 1 13 12 5 3 2.5 14 12 5 3 1 1.5 15 12 5 3 2 1.5 16 12 5 3 2.5 1.5 17 12 5 3 18 17 3 3 19 12 0.3 0.1 2 2 20 1.2 1.0 (Cu=2.5 Mg=1.5) 0.1 Each of the aluminum alloy powders thus prepared was cold pressed to a preform 30 mm in diameter and 80 mm in height and then extruded at 450°C at an extrusion ratio of 3. Test pieces were prepared from the extruded materials, and tensile tests and creep tests were conducted at 300°C. In Table 2, "rupture time" indicates the period of time required for a test piece to rupture when it is exposed to a stress of 78.4 MPa(8 kg/mm²) at 300°C. Results are given in Table 2 below. No. Tensile strength (MPa) (kg/mm²) Elongation (%) Rupture time (Hr) 1 198.9 (20.3) 11.0 1020 2 208.7 (21.3) 13.0 1187 3 203.8 (20.8) 12.5 258 4 215.6 (22.0) 10.5 3610 5 225.4 (23.0) 4.2 105 6 217.6 (22.2) 2.3 421 7 220.5 (22.5) 1.5 358 8 245.0 (25.0) 1.8 2563 9 208.7 (21.3) 5.9 125 10 227.4 (23.2) 1.2 2054 11 243.0 (24.8) 1.8 1823 12 230.3 (23.5) 1.9 435 13 240.1 (24.5) 9.1 4350 14 242.1 (24.7) 8.9 2895 15 255.8 (26.1) 7.1 4568 16 265,6 (27.1) 4.5 5015 17 191.1 (19.5) 15.7 2.6 18 198.9 (20.3) 15.3 2.2 19 139.2 (14.2) 17.9 0.3 20 96.0 (9.8) 22.7 1.3 Table 2 indicates that the extruded materials obtained from the aluminum alloys of the invention have high tensile strength and elongation and exhibit good resistance to creep. Particularly, the extruded products produced from alloy Nos.13 to 16 are better balanced in resistance to creep, tensile strength at elevated temperatures and toughness. In contrast, aluminum alloys containing alloying elements in amounts outside the range of the invention give products low in tensile strength at 300°C and short in rupture time. It is noted that the alloy No.20 which is known to be highly resistant to heat among conventional IM materials is extremely inferior to the alloys of the invention in the strength and resistance to creep at 300°C.

Claims: An aluminum alloy comprising 5 to 30% by weight of Si, 2 to 5% by weight of Fe, 2 to 5% by weight of Ni, 0.5 to 3% by weight of Mo, 0.5 to 3% by weight of Zr and aluminum in a remaining amount provided that the total amount of Mo and Zr is in the range of more than 2% by weight and less than 5% by weight. An aluminum alloy product produced by extruding an aluminum alloy material in powdery form, the aluminum alloy having a composition according to claim 1. An aluminum alloy product according to claim 2 wherein the aluminum alloy material is extruded at a temperature between 400 to 500°C and at an extrusion ratio of 2 to 10. An aluminum alloy product according to claim 3 wherein the aluminum alloy material is extruded at an extrusion ratio of 2 to 5.

Inventors: KAWAI MASAHIKO, KUSUI JUN, KAWAI, MASAHIKO, KUSUI, JUN
Applicants: TOYO ALUMINIUM KK, TOYO ALUMINIUM KABUSHIKI KAISHA
Application year: 1989
Main classification: C22C1
IPC codes: C22C1, C22C21