Microstructure Evolution during Cooling Slope Rheoprocessing of Novel Al-15Mg<sub>2</sub>Si-4.5Si Composite

Abstract

In this study, microstructure evolution during cooling slope casting of Al-15Mg2Si-4.5Si composite is studied considering a test case of melt pouring temperature of 650°C. The shear force exerted by the flowing melt on the evolving primary Mg2Si and α-Al grains facilitates their fragmentation and subsequent spherodisation. After leaving cooling slope, the composite slurry is kept isothermally within a holding furnace for different time duration i.e., 8, 16, 24 and 32 minutes. Increasing trend in grain size values is observed with the increasing slurry holding time, whereas sphericity value decreases after initial increase till 8 minutes of slurry holding. The slurry samples are scooped from chosen locations of the slope as well as from isothermal slurry holding bath and rapidly quenched in oil to study their microstructure and mechanical properties. Simultaneous spherodisation of both the primary phases i.e., primary Mg2Si and α-Al during cooling slope processing is evident from optical microscopy and Scanning electron microscopy of quenched slurry samples. Whereas increasing sphericity of P-Mg2Si and α-Al phases, along the melt flow direction over the slope, is found to accompany with the increasing micro hardness values.