Effect of strontium and strontium-magnesium additions on the microstructure and mechanical properties of hypereutectic Al-17Si alloy

Al-17Si, Al-17Si-0,1Sr and Al-17Si-0.1Sr-0,6Mg alloys were produced by permanent mold casting method. The structural and mechanical properties of the alloys were determined by the investigations carried out on specimens prepared by machining of the produced alloy ingots. The microstructural examinations were carried out on specimens prepared by standard metallographic methods but without etching. Their hardness and mechanical properties were determined by Brinell hardness measurement method and universal tensile tests, respectively. The microstructure of the binary Al-17Si alloy consisted of aluminum-rich α dendrites, primary silicon, eutectic Al-Si and βphases. Ternary Al-17Si-0.1Sr alloy contained AlxSiySrz phase in addition to phases in the binary Al-17Si alloy. It was observed that the 0.6% magnesium addition to the ternary Al-17Si-0.1Sr alloy cause to form of Mg2Si phase in the microstructure of this alloy. The values of the hardness, yield strength, tensile strength and elongation to fracture of Al-17Si alloy were measured as 57 BSD, 93.7 MPa, 127.6 MPa and 2.4%, respectively. These values were measured as 55 BSD, 95.2 MPa, 137.9 MPa and 2.9% in Al-17Si-0.1Sr alloy and 70 BSD, 123.2 MPa, 141.1 MPa and 1.1% in Al-17Si-0.1Sr-0.6Mg alloy. The addition of strontium reduced the hardness of the binary Al-7Si alloy to a lesser degree but improved the yield and tensile strength and elongation to fracture values. Magnesium addition significantly increased the yield and tensile strength of the ternary Al-17Si-0.1Sr alloy but decreased their elongation to fracture. The effects of strontium and strontium-magnesium additions on the mechanical properties of the Al-17Si alloy were discussed in terms of their structural properties