Investigation of the effect of T6 heat treatment on machinability properties in milling of Al-7Si-Mg and Al-7Si-0.6Mg alloys

In this study, Al-7Si-Mg and Al-7Si-0.6Mg alloys were produced using the permanent mold casting method. Solution, quenching and artificial aging processes were carried out on these alloys within the scope of T6 heat treatment. Microstructural, mechanical and machinability properties in milling process of as-cast and T6 heattreated alloys were investigated. The microstructure of the as-cast Al-7Si-Mg alloy consisted of α-Al, primary Si, eutectic Al-Si, Mg2Si, β-Al(Fe, Mn)Si, β-Al5FeSi and π-AlSiMgFe phases. In addition to the existing phases, β-Al8Mg3FeSi6 phase was observed in the microstructure of the Al-7Si-0.6Mg alloy. It was determined that the phases in the microstructure became spheroidization and homogeneously distributed with T6 heat treatment. It was determined that the hardness, yield and tensile strengths increased with the heat treatment applied to the alloys, while the elongation to fracture decreased. It was observed that Al-7Si-0.6Mg alloy exhibited better mechanical properties. The cutting force, surface roughness, built-up layer (BUL) and built-up edge (BUE) decreased with the increase in cutting speed in the machinability tests, while it increased with the increase in feed rate. T6 heat treatment improved the machinability properties of the alloys due to the decrease in elongation to fracture. Al- 7Si-0.6Mg alloy in both the as-cast and heat-treated condition exhibited better machinability properties. Lower cutting force, surface roughness, BUL and BUE were obtained in the machinability tests performed with TiAlN coated carbide end mills. Optimal machinability properties were obtained in machining of Al-7Si-0.6Mg alloy in T6 heat-treated condition with TiAlN coated carbide end mills at cutting speed of 110 m/min and feed rate of 0.08 mm/rev conditions.