An Evaluation of Severe Plastic Deformation on the Densification Behaviour of Powder Metallurgy Aluminium Alloy Al-Mg-Si-Cu-Fe and Al-Zn-Mg-Cu

Abstract

Light weight aluminium alloys, showing excellent workability, high thermal and electrical conductivity, represent a good choice for the powder metallurgy (PM) industry to produce new materials having unique capabilities, not currently available in any other powder metal parts. Moreover the requirement on mechanical properties (i.e. high tensile strength with adequate plasticity) should assure an increasing role for aluminium alloys in the expanding PM market. Room temperature tensile strengths in aluminium based metal matrix composites (MMC) in excess of 800 MPa have been reported (Guo & Kazama, 1997). However, PM based MMC currently show very limited application, also due to the high costs of production, thus having a low commercial appeal for both producers and end users. The application for aluminium powders is basically in the production of PM parts for structural and nonstructural purposes in the transportation and commercial areas. Press and sinter products, blends of aluminium and elemental alloy powders are pressed into intricate configurations and sintered to yield net or near-net shapes. There are two interesting classes of commercial press and sinter aluminium alloys: Al-Mg-Si-Cu and Al-Zn-Mg-Cu-(Si). The first alloy displays moderate strength (the level of tensile strength is 240 MPa) while the latter alloy develops high mechanical properties (the level of tensile strength is 330 MPa) in both the assintered and heat-treated conditions. Solid solution strengthening and precipitation hardening can contribute to the higher strength values of the commercial alloys. (Pieczonka et al., 2008) report transverse strength of aluminium-based PM alloys in the range of 400 MPa (Al-Mg-Si-Cu) to 550 MPa (Al-Zn-Mg-Cu). It’s well known (Bidulska et al., 2008 a) that conventional forming methods and heat treatment can determine a limit in the level of strength-plastic characteristics adequate to structural properties. One possible way for achieving higher mechanical properties is