Simultaneously strengthening and toughening a core-shell structured particulate reinforced aluminum alloy-based composite by solid solution treatment

To improve the ductility of particulate reinforced metal matrix composite, an A356 aluminum alloy based composite reinforced with in-situ spheroidal core-shell structured (CS) particulates was fabricated via powder thixoforming. The generated CS particulates have a uniform two-layered annular intermetallic shell surrounding a Ti core, which renders the composite an excellent elongation of 12% equivalent to that of the A356 alloy, while maintaining a high strength. Subsequent solution treatment at 530 °C for 3 h further improve its ultimate tensile strength, yield strength and elongation from 230 MPa, 138 MPa and 12% to 243 MPa, 168 MPa and 17%, respectively, i.e., the strength and ductility are simultaneously improved. The microstructure evolution, particularly the evolution of the CS particulates during solution treatment, the resulted mechanical properties and corresponding strengthening as well as toughening mechanism were comprehensively discussed. A modified shear lag model established by introducing an equivalent coefficient into the particulate fraction aimed at the CS particulates and taking the strengthening role of eutectics into account can reasonably describe the strengthening mechanisms and accurately predict the yield strength of the composite during solution treatment. But the achieved toughening model through simplifying both the particulates and eutectic into equivalent monolithic particulates can only accurately calculate the changing tendency of ductility with the solution time and partially depict the toughening mechanisms, which should be further clarified in future.