The effect of Sb addition on microstructures and tensile properties of extruded Al–20Mg2Si–4Cu alloy

Abstract

This work was carried out to investigate the relationship between microstructures and mechanical properties of extruded Al–20Mg2Si–4Cu alloys unmodified and modified with 0.5wt% Sb addition at room and high temperatures. Various techniques including metallography, field emission scanning electron microscope, differential thermal analysis and scanning electron microscopy were used to characterize the microstructure, tensile behavior and fracture mechanism of the alloys. It was found that 0.5wt% Sb additions were highly effective in refining microstructures by changing the morphology of primary Mg2Si from coarse dendrite into smaller polyhedral shape with average size less than 20µm. Tensile test showed that ultimate tensile strength (UTS) of the modified alloy increased dramatically to 283MPa at room temperature and 213MPa at 150°C, evidently higher than the 220MPa and 185MPa for the unmodified alloy, respectively. Fracture surface examinations revealed a transition from particle fracture of primary Mg2Si in the unmodified alloy to particle–matrix interface debonding in the modified alloy. The transformation of primary Mg2Si from coarse dendrites to refined polygonal shapes contributes to the enhanced strength and ductility of the modified alloy, since the polygonal primary Mg2Si particles dispersed uniformly in modified alloy, impeding dislocation motions and freeing stress concentrations. A schematic map was established to further elucidate the mechanisms of fracture behavior during stretching process.