Effect of addition of the boron, strontium and/or magnesium on the structural and mechanical properties of the Al-Si alloys

In this study, a series binary Al-Si, ternary, and quaternary Al-Si based alloys having different rate silicon, boron and (or) strontium and magnesium and one quinary Al-12Si-0.05B-0.1Sr-0.6Mg were produced by permanent mould casting. Structural properties of the produced alloys were investigated by using standard metallographic technics. Their hardness values and mechanical properties were determined by using Brinell hardness test method and universal tensile test, respectively. The microstructure of the binary Al-Si alloys consisted of aluminum rich α dendrites, primary Si and eutectic Al-Si phase. Addition of boron to Al-Si alloys caused a decrease in the size of the aluminum rich α phase and a change in morphology of the eutectic phase. The ternary Al-Si based alloys contained strontium showed a microstructure having the refined and spheroidized eutectic phase compare to binary Al-Si alloys. Magnesium had no significant effect on the microstructures of Al-Si-Sr alloys. However, magnesium rich phases observed in the microstructure of the quaternary Al-Si-Sr-Mg alloys. Specific ratios of boron, strontium and magnesium additions caused an increament the both hardness and tensile strength of the produced alloys. Increament in the hardnes and tensile strength, and the change in elongation to fracture values of the alloys investigated were discussed in the basis on structural changes caused by element additions.