Effect of Isothermal Holding on Semisolid Microstructure of Al–Mg2Si Composites

Effect of heat treatment and isothermal holding has been investigated on the microstructure and degree of globularity of Al–Mg 2 Si composites. Different contents of reinforcement, 15, 20, and 25% have been used in this study. Isothermal holding experiments were conducted at 585 °C for 140 min. Results showed that, upon heat treatment, grain size of dendrites was reduced while the degree of nodularity was increased. Results of nodularity were obtained using an image-analyzing software which gives the distribution of radius of curvature for different phases of particles. According to the results, in contrast to Al–15 and 25% Mg 2 Si, isothermal holding significantly influenced the microstructure of Al–20% Mg 2 Si composites. Two companion mechanisms have been proposed for the generation of globular grains. SEM investigations were also employed to confirm the optical observations.