The combined effects of Sr additions and heat treatment on the microstructure and mechanical properties of high pressure die cast A383 alloy

The microstructures and mechanical properties of high pressure die cast A383 alloys under four conditions (with and without Sr additions and heat treatment) were investigated. Sr addition is responsible for the increase in the elongation of high pressure die cast A383 alloys by refining the eutectic Si particles from long, needle-like morphologies to fine, fibrous ones. High cooling rates, as generated in the high pressure die casting process, also significantly contribute to the microstructural refinement of the eutectic Si particles. However, there was almost no relationship between the morphologies (size and roundness) of the eutectic Si particles and the yield strength of high pressure die cast A383 alloys. Heat treatment (aging without solution treatment) increased the yield strength of high pressure die cast A383 alloys. Sr addition combined with heat treatment was found to refine the size of aging precipitates and therefore improve the yield strength beyond the levels observed for heat treatment alone. The sludge characteristics (size, roundness and fraction) were not affected by the different heat treatments and Sr additions and had no discernible effect on the change in mechanical properties.