Characteristics of rapidly solidified Al-Si-X powders for high-performance applications

Abstract

Among the variety of new aluminium alloys, the Al-Si-X P/M system appears to be the most suitable for high-performance applications in the automobile industry. Our work concerns the research on the possible application of this system for products with enhanced wear and high-temperature resistance. This paper presents the characteristics of the air-atomized J1 (Al-20Si-3Cu-1Mg), J2 (Al-20Si-3Cu-1Mg-5Fe), J3 (Al-20Si-3Cu-1Mg-7.5Ni), K1 (Al-20Si-5Fe-2Ni), and the argon-atomized K2 (Al-20Si-5Fe-2Ni) powders, aimed at optimizing the processing conditions of the final products, in terms of production techniques, powder morphologies, powder sizes and size distributions, cooling rates, specific areas, surface oxide thicknesses and oxygen contents. Atomization in air (J1, J2, J3, K1) and atomization in argon (K2) resulted in morphologically different powders. Particle-size distributions were similar, indicating cooling rates of ∼104 to 106 K sec−1. This cooling range proves that the theoretical estimate presented in this work is sufficiently accurate. Al-Si-X P/M alloys consisted of primary and eutectic silicon crystals in an aluminium matrix (J1) plus intermetallic compounds (J2, J3, K1, K2). Air-atomized powders with different chemical composition showed an average oxide thickness of ∼30 to 40 nm. In powders with equal chemical composition, an inert atomization atmosphere produced powders with smaller surface area, lower amount of oxygen, and thinner total oxide thickness. The composition of surface oxides was strongly influenced by the chemical composition but the thickness was mainly influenced by the atomization atmosphere.