Mechanical properties and fracture of in-situ Al3Ti particulate reinforced A356 composites

Abstract

The microstructure and mechanical properties of in-situ 5 vol. % Al3Ti/A356 composites were studied either taking account of the effects of T6 heat treatment and strontium (Sr) addition or not. For both as-cast and T6 treated composites, the in-situ Al3Ti particulates are in a blocky morphology with average size of 5–6 μm. Sr modified the Si particulates by reducing their size and aspect ratio, without a noticeable influence on the Al3Ti particulates. Energy dispersive X-Ray spectroscopy (EDS) revealed the existence of Si in the blocky Al3Ti particulates in the as-cast composites likely to form an (Al,Si)3Ti phase. Solutionization at 540 °C for 4 h resulted in the enrichment of Si inside the Al3Ti particulates, raising a question about the stability of (Al,Si)3Ti as reported by others. For both as-cast and T6 treated A356 alloy, the yield strengths were enhanced by in-situ Al3Ti particles, but the elongation was adversely affected. In comparison, the tensile strength and ductility of the Al3Ti/A356 were simultaneous improved with the modification of Sr due mainly to the modification of eutectic Si particles. Microstructure-based representative volume element (RVE) simulations revealed the microscale damage evolution of the studied materials and provided a good prediction of their fracture behavior, substantiated by fractography.