Effect of strontium additions on the microstructural and mechanical properties of Al-17Si-4Cu-0.6Mg-3Zn (B390+2 wt%Zn) alloy

Abstract

One Al-17Si-4Cu-0.6Mg-3Zn (B390 + 2 wt%Zn) alloy and five B390 + 2 wt% Zn-Sr alloys were produced by permanent mold casting method. Microstructural evaluations were carried out with microscopic techniques. The phases of the alloys are confirmed with the X-ray diffraction (XRD) studies. The hardness, tensile strength, and elongation to fracture values of the alloys were determined by the Brinell hardness measurement method and tensile tests. It was observed that microstructure of the B390 + 2 wt%Zn alloy consisted of alpha-Al, eutectic and primary silicon particles, theta (CuAl2), beta (Al5FeSi), delta (Al4FeSi2), and alpha-Al-15(FeMnCu)(3)Si-2 phases. Sr addition caused significant modification in both eutectic and primary Si particles. It also caused morphology and shape changes in the other phases of the Al-17Si-4Cu-0.6Mg-3Zn alloy. When the strontium ratio exceeded 0.075 wt%, intermetallic Al2Si2Sr and mu (Al-Fe-Si-Mn) phases were formed in the alloy. Hardness and tensile strength of the B390 + 2 wt%Zn-Sr alloys increased significantly with increasing Sr ratio up to 0.075 wt%. Elongation to fracture value of B390 + 2wt%Zn alloy increased with 0.01 wt% Sr addition, but above this level, it decreased continuously with increasing Sr content. The changes caused by the Sr additions in the mechanical properties of the tested alloys were discussed in the basis of microstructural changes observed due to Sr additions.