Enhanced strength and ductility of A356 alloy due to composite effect of near-rapid solidification and thermo-mechanical treatment

The coarse dendritic microstructure with non-uniform distribution of eutectic Si particles leads to poor ductility of A356 alloy, thus challenging the enhancement of mechanical properties through deformation at room temperature. Here, a new processing protocol was proposed by combining near-rapid solidification with two-step thermo-mechanical treatment (TMT). To significantly improve the ductility of the alloy, near-rapid solidification, in combination with first-step TMT including equal channel angular pressing (ECAP) and intermediate heat treatment, was applied to refine eutectic Si particles and make them evenly distributed in the matrix. On this basis, a high ultimate tensile strength ∼483 MPa, with relatively good elongation to failure ∼8.1% can be achieved by the subsequent ageing treatment and composite deformation (ECAP + cryorolling) of second-step TMT. The excellent combination of strength and ductility was mainly attributed to the synergistic effect of high density of dislocations, refined nanoscale Si particles and uniform distributed eutectic Si particles arising from this fabrication processing. This work provides a new idea for the preparation of high strength Al-Si cast aluminum alloy, so that the application of Al-Si cast alloy is promisingly expected to expand.