Effect of complex modification of Al-5Ti and Al-3P on hypereutectic Al-18Si alloys

The solidification microstructure, fracture morphologies, and mechanical properties of an Al-18Si alloy and alloys modified with Al-5Ti and Al-3P master alloys were investigated using an optical microscope, scanning electron microscope, and an electronic universal testing machine. The results show that additions of Al-5Ti and Al-3P have significant effects on the size and area fraction of the primary Si and the mechanical properties of the Al-18Si alloy. Compared to the Al-18Si alloy modified with 0.6 wt% Al-5Ti at 850 °C, when the Al-18Si alloy was modified with 0.3 wt% Al-5Ti and 0.5 wt% Al-3P at the same temperature, the average size of the primary Si decreased from 39 to 14 μm and the area fraction increased from 9.5% to 11.6%. The biggest influencing factor on the tensile strength and elongation of the Al-18Si alloy is the addition of Al-3P, followed by the modification temperature and the addition of Al-5Ti. At a modification temperature of 850 °C, the tensile strength and elongation of the Al-18Si alloy modified with 0.3 wt% Al-5Ti+0.5 wt% Al-3P increased by 19.6% and 88.6%, respectively compared to that of the Al-18Si alloy modified with 0.6 wt% Al-5Ti.