Investigation of the effect of zinc and copper additives on machinability properties of Al-7Si alloy

In this study, binary Al-7Si, ternary Al-7Si-4Zn and quaternary Al-7Si-4Zn-3Cu alloys were produced by using permanent mould casting method. The internal structure images of the produced alloys were obtained using an optical microscope. The internal structure of the binary Al-7Si alloy consisted of aluminum-rich α, primary silicon crystals and eutectic Al-Si phase. The addition of 4% zinc to the Al-7Si alloy did not create a new phase in the alloy's internal structure. It was determined that Al2Cu (θ) phase was formed in addition to ternary alloy in Al-7Si-4Zn-3Cu alloy. Brinell hardness measurement method was used for the hardness of the produced alloys and Vickers hardness measurement method was used for the hardness of the internal structures. The tensile strength and breaking elongation values of the alloys were determined using a universal tensile tester. It was observed that zinc and copper additives added to Al-7Si alloy increased the hardness and tensile strength of the alloys and decreased breaking elongation. Alloys were prepared for drilling with turning and milling operations. Drilling experiments were carried out with constant cutting speed (120 m/min) and feed rate (0.15 mm/rev) values using uncoated carbide drills. The highest thrust force was observed in Al-7Si alloy while the lowest thrust force was observed in Al-7Si-4Zn-3Cu alloy. It was determined that the formation of BUE (Built up edge) was mostly in Al-7Si and Al-7Si-4Zn alloys. The results obtained from the machinability experiments were explained based on the mechanical and internal structure properties of the alloys.