Enhanced mechanical properties of Al-Si-Cu-Mg(-Fe) alloys by a deformation-semisolid extrusion process

Al 4.5 wt% Si 1 wt% Cu 0.3 wt% Mg(-1 wt% Fe) alloys fabricated by a deformation-semi-solid extrusion (D SSE) process have been investigated by means of differential scanning calorimetry (DSC), optical microscope, field emission scanning electron microscope (FE-SEM) and electron backscatter diffraction (EBSD) analysis. Rounded Si particles were slightly broken during the D-SSE process, while platelet Fe-intermetallic compounds (Fe-IMCs) were significantly fragmented into segments. The average sizes of the Fe-IMCs and Si particles in the as-extruded 1 Fe alloy were 2.6 and 3.9 mu m, respectively. A high number density of dispersed Fe-IMCs existed in the matrix during the D-SSE process. Tensile results indicate that the ultimate tensile strength of as-extruded 1 Fe alloy appears at 16% of elongation and that the specimen eventually fractured at 28% of elongation, showing local elongation with necking. The stress decreases from the ultimate tensile strength to failure. It is considered that the fragmented Fe-IMCs have a beneficial effect on the elongation since they were uniformly fragmented and dispersed. Brittle fracture was characterized by a pattern of cleavage at coarse Fe-IMCs in the as-cast 1 Fe, whereas the formation and coalescence of voids resulted from fragmented Fe-IMCs of the as-extruded 1 Fe. This contributed to considerable localized plastic deformation of the as-extruded 1 Fe alloy. Strain distribution of the secondary particle was evaluated by local average misorientation.