Effects of sintering time on the microstructure and properties of an Al-Cu-Mg alloy

Cold pressing and conventional sintering was used to prepare an Al-Cu-Mg alloy and the effects of isothermal sintering time at 620℃ on evolution of the microstructure were studied. The results showed that at an isothermal sintering time of 30 min, the eutectic liquid of Al-Mg, Al-Cu-Mg and Al-Cu filled the particle gaps, resulting in a reduction of pores and rapid densification of the alloy; at isothermal sintering times of 30−120 min, the grains began to grow continuously which increased the density of the alloy a little; at 180 min, a large number of micropores appeared in the alloy which caused the density to decrease. Examination of the alloy micro-area elements showed that Cu diffused from the grain core to the grain boundary during sintering, which promoted the hard and brittle θ phase at the grain boundary. This increased the grain boundary strength and hence the tensile strength and hardness of the alloy. At an isothermal sintering time of 180 min, the strength of the alloy decreased. Optimum mechanical properties of the alloy were obtained at an isothermal sintering time of 120 min, the tensile strength and elongation were 237.9 MPa and 12.67% respectively, and the hardness was 87.7 HBW. A spinel phase, observed at the grain boundary of the aluminum alloy, provided evidence for the role of Mg in destroying the oxide film to promote sintering of the liquid phase.