Age hardening of Al-7Si-0.5Mg alloy: Role of Si size and distribution

The age-hardening behavior of the Al-7Si-0.5Mg alloy with different size and distribution of Si phase was investigated. The wedge-shaped mold was used to prepare specimens with different characteristics of Si. The specimen with fine and homogeneous Si showed accelerated age-hardening kinetics and higher peak hardness than the one with coarse and clustered Si due to the higher dislocation density resulted from the mismatch in the thermal contraction of Si and Al. The overlapping of the plastically-affected zone of the adjacent Si phase in the specimen with large and clustered Si led to a reduced volume fraction of the plastically-affected zone, lower dislocation density and lower age-hardening kinetics. The relationship between the radius of Si and the critical inter-particle spacing that minimize the interaction of adjacent Si to maximize the dislocation density and accelerate age-hardening kinetics was established.