Investigation of sintering densification mechanisms in aluminum alloys with compacted and loose powder states

An Al–Cu–Mg–Si–Sn alloy was fabricated via both press-and-sinter powder metallurgy (PM) and metal injection molding (MIM) routes to investigate the sintering densification behavior of aluminum alloy powders in compacted and loosely packed states. The results demonstrate that the initial powder packing state has a pronounced influence on both the wetting kinetics and the development of sintering stress during transient liquid-phase sintering. Specifically, liquid-phase formation and phase transformations during sintering are essentially identical in the PM and MIM alloys. However, owing to its higher green density, the PM alloy undergoes solid-state sintering after disruption of the surface oxide film on aluminum particles. When liquid phases are formed in the aluminum alloy, the PM alloy exhibits faster wetting kinetics and greater sintering stress, resulting in a significantly higher densification rate than that of the MIM alloy. Furthermore, following oxide film disruption, a semi-continuous Al–Mg–O layer forms along the prior particle boundaries, which adversely affects the mechanical properties of the PM alloy. This microstructural feature provides a mechanistic explanation for why aluminum alloys produced via the PM route generally exhibit lower tensile strength and ductility than their wrought counterparts.