EFFECTS OF CU AND SOLUTION HEAT TREATMENT ON THE MICROSTRUCTURE AND HARDNESS OF IN-SITU ALUMINIUM MATRIX COMPOSITE CONTAINING AL۴SR PHASE

This study was undertaken to investigate the effects of Cu and solution heat treatment on the microstructure and hardness of cast Al-Al۴Sr metal matrix composite. Different amounts of Cu (۰.۳, ۰.۵, ۱, ۳ and ۵ wt.%) were added to the composite. Specimens were heat treated at ۵۰۰ °C for ۴ hours followed by water quenching. Microstructural studies were assessed by the use of optical microscope, scanning electron microscope (SEM) and x-ray diffractometry (XRD). The results showed that addition of ۵ wt.% Cu reduces the length of large needle-like Al۴Sr phase and refines the microstructure. In addition, the presence of Cu-intermetallics increases hardness of the composite. Cu mainly forms θ phase which segregates at the grain boundaries. Heat treatment partially dissolves Cu-intermetallics and homogenizes the distribution of θ phase in the matrix.