Effects of processing conditions on the sintering response of hypereutectic Al–Si–Cu–Mg P/M alloys

The processing conditions for the commercial press-and-sinter powder, Ecka Alumix 231 with the nominal composition of Al–15Si–2.5Cu–0.5 Mg(wt%) have been optimized in this study. It has been found that densification of Ecka Alumix 231 depended largely on the sintering atmosphere and the amount of liquid phase presented. Three different sintering atmospheres: nitrogen, vacuum and nitrogen with 3% hydrogen have been investigated. Nitrogen atmosphere was found to be the most efficacious sintering atmosphere due to the formation of AIN which later induced pore filling effect. Presence of hydrogen in the sintering atmosphere caused detrimental effect on sintering response due to the formation of MgH2 which decomposed at higher temperature and led to an increase in the pore pressure. Pore swelling effect occurred and inhibited compact densification. The optimum sintering conditions for Ecka Alumix 231 is determined to be at 560 °C (in the presence of 15% liquid content) under nitrogen atmosphere to yield compacts with higher sintered density, less porosity and better mechanical properties.