Improvement of Mechanical Properties of A Hypereutectic Aluminum-Silicon P/M Alloys

Abstract

Aluminum-Silicon P/M alloys have been of particular interest as these materials offer the advantage of high-wear resistance, high strength, good temperature resistance, and a low coefficient of thermal expansion. More recently, a novel hypereutectic aluminum-silicon alloy referred to as “Alumix-231” has emerged. The first known Al-Si commercial press and sinter P/M system, this alloy is manufactured by Ecka Granules and has a nominal composition of Al-14Si-2.5Cu-0.5Mg. The powder was compressed by using dual action press machine with compaction pressure from 300-700 MPa. Green density increased with increasing compaction pressure. And highest green density was obtained by using 700 MPa compaction pressure for ~91% relative green density. All samples were sintered in a tube furnace under a flowing nitrogen atmosphere. Sintering temperature is from 550-600oC for 30-120 minutes and 5-15oC/min heating rate. Before reach sintering temperature, compacted powder were dewaxed at 400oC for 20 minutes. Highest sintered properties (exp. Sintered density, hardness) was obtained by using 590oC sintering temperature for ~97% sintered density, 83 HRB hardness and tensile strength for 186.54 MPa. And at optical microscopy also showed highest densification on this sample. T6 heat treatment was carried out to observe the effect of heat treatment to the alloy. The optimum heat treatment involved solutionizing the samples at 512oC for 50 minutes, followed by water quenching, and artificially aging the samples at 173oC for 24 hour. And there is improvement of hardness and tensile strength from heat treated samples for ~49.5 HRD(~107 HRB) and ~280 MPa. It is concluded that θ phases were the dominate precipitates formed during heat treatment.