Influence of Microstructure and Turning Inserts on Machinability and Surface Characteristics of Hypereutectic Al-Si Cast Alloys

摘要

The microstructures, machinability and surface characteristics of hypereutectic Al-Si cast alloys were studied after various melt treatments like refinement and modification. Results indicate that combined refined and modified Al-17Si-4.5Cu cast alloys have microstructures consisting of uniformly distributed primary silicon, interdendritic network of fine eutectic Al-Silicon and fine CuAl_2 particles in the interdendritic region. These alloys exhibited better machinability and surface finish in the cast condition as compared with the same alloy subjected to only refinement or modification. Performances of the turning inserts (Vn-coated, PVD and Polished CVD diamond-coated) were evaluated in machining hypereutectlc Al-Si cast alloys under dry environment using a lathe. The Polished CVD diamond-coated insert outperformed the Vn-coated or PVD-coated cutting inserts which suffered from sizeable edge buildup leading to higher cutting force and poor surface finish. The Polished CVD diamond-coated insert shows a very small steady wear without flaking of the diamond film during cutting. This paper attempts to investigate the influence of refinement, modification and combined action of both on the microstrutural changes in the hypereutectlc Al-Si cast alloys and their machinability and surface finish when different turning inserts used.