Elucidating the Effects of Cu and Hot-Extrusion on Tensile Properties of Al–AlSb In Situ Composite

The microstructures, hardness and tensile properties of Al–AlSb-xCu in situ composites have been studied where the amount of Sb was 10 wt% and Cu contents were 1, 3, 5, 7 and 10 wt% Cu. Microstructural studies indicated that depending Cu content, the crystals of primary AlSb alter seriously in shape and size, and also a new Cu-intermetallic (Al₂Cu) is formed in the as-cast microstructure. Although T6 heat treatment did not affect primary AlSb phase, extrusion process refined it through fragmentation mechanism. A uniform microstructure including well distributed fine primary AlSb particles was found by adding 5 wt% Cu to the Al–AlSb composite, as an optimum content. The variation of hardness results with Cu addition showed an increasing trend, while tensile testing examinations revealed that by exceeding Cu content (> 5 wt%), the ultimate tensile strength (UTS) of the composites is reduced in both as-cast and T6 states. The effect of heat treatment on elongation improvement of the extruded composite was positive; however, it was reverse in as-cast condition, since extruded specimens showed a better response to removing the CuAl₂ phase in the eutectic region during heat treatment. Remarkable enhancement in the UTS and elongation values of the extruded specimens, before and after heat treatment, was attributed to the extensive fragmentation of intermetallic phases and well distributed fine particles in the matrix which provided proper obstacles for dislocation motion. The fracture behavior of intermetallics in as-cast specimens showed more cleavage fracture in comparison with extruded and heat treated composites which demonstrated more dimples.