Effect of as-cast microstructure heterogeneity on aging behavior of a high-pressure die-cast A380 alloy

Microstructure and hardness evolution of a vacuum-assistant die-cast A380 alloy during heat treatment were investigated. Both surface layer and central region of the casting component were analyzed in die-cast state, solutionized state and artificial age state. During the artificial age, the surface layer hardened more significantly than the central region due to faster precipitation and more refined hardening phases in the surface layer. Detailed analysis on the macro-segregation, microstructure morphology and grain size revealed that the different aging behaviors exhibiting in the surface and the central region were mainly attributed to a combining effect of the enrichment of Si and Cu at the surface layer, the fully-divorced morphology of eutectic in die-cast microstructure, and the presence of the externally solidified crystals at the central region. The presence of the Si particles, which exhibited quite different thermal expansion properties, changed the density and the distribution of the dislocations in the α-Al matrix, and consequently changed the precipitation of the hardening phases.