Effects of hot extrusion prior to spheroidization on Al-Si-Cu alloys

The influence of prior hot extrusion of an Al-7%Si-0.5%Mg-3%Cu alloy on the subsequently spheroidized microstructure was studied. Such extrusion promoted a greater degree of spheroidization, smaller alpha globules, and higher levels of entrapped eutectic and entrapped Cu-rich phase, but no net change in copper concentration in the alpha globules (other than the entrapment). The greater degree of spheroidization and the smaller globule size are expected to increase semi-solid formability, but the higher level of entrapped eutectic is expected to slightly reduce semi-solid formability. In samples which were T6 heat treated after spheroidization, the pre-spheroidization extrusion caused an increase of 0.5% Cu in the alpha, but no change in microhardness of either the primary alpha or the eutectic.