Microstructure and Mechanical Properties of Squeeze Cast Al-5 Mg-3Zn-1Cu-1Si Alloy Along Cross Section

Abstract

The variation of microstructure and mechanical properties along the cross section of squeeze cast Al-5Mg-3Zn-1Cu-1Si alloy is studied under both squeeze-cast and peak-aged condition (470 °C × 24 h + 125 °C × 24 h). For squeeze-cast alloy, along the depth direction, second dendrite arm space and the percentage of $${\alpha }$$-Al increase significantly, while the volume fraction of T-Mg32(AlZnCu)49 and Mg2Si phase showed a dramatic decrease. The ultimate tensile strength of squeeze-cast alloy slightly decreased from 357.04 MPa for the surface layer to 344.21 MPa for the central layer, yield strength dropped from 296.86 MPa to 241.03 MPa, but the elongation almost tripled from 1.42% to 3.78%. After peak aging, the ultimate tensile strength of surface layer and central layer reached 538.45 MPa and 504.03 MPa, yield strength reached 447.46 MPa and 442.65 MPa, and the elongation reached 5.23% and 3.97% respectively. Meanwhile the difference of ultimate tensile strength and elongation was increased, but that of yield strength reduced after aging treatment. Precipitation strengthening is the main strengthening mechanism while the improvement in ductility is due to the dissolution of T-Mg32(AlZnCu)49 and the morphological change of eutectic Mg2Si.