Synergistic Effect of Sr and Ca Combined Additions on the Microstructure of A390 Aluminum Alloy

Effects of Sr and Ca combined additions (Sr+Ca=0.05wt/%) on the microstructure of A390 aluminum alloy were evaluated by investigating the variation of quantity, size and shape of primary silicon, eutectic silicon, primary α phase and intermetallic phase. The results show that the variation of microstructures results from the synergistic effect of Sr-Ca additions. The loss rate of Sr is reduced with a small amount of Ca; meanwhile, the coarsening effect of primary silicon phase arising from Sr addition is also suppressed. The Sr in A390 aluminum alloy mainly modifies eutectic silicon phase and refines θ phase. Furthermore, Ca principally modifies primary silicon phase and primary α phase. The optimal microstructure is obtained when combined addition of 0.05%Sr-Ca is applied and the atomic ratio of Sr and Ca is 5:1, in which primary silicon phase and eutectic silicon phase as well as primary α phase are all modified significantly compared with those of only 0.05% Sr addition.