Deformation-induced phase changes of Zn-Al alloy during ultra-precision raster milling

Abstract

Metal cutting is a complex material removal process with elastic deformation (ED) and plastic deformation (PD) together taking place in chip formation and surface generation. PD consists of shear PD (SPD) and normal PD (NPD) intrinsically relevant to cutting mechanism, such as pure cutting and ploughing. In ultra-precision machining, PD induces phase changes of Zn-Al alloy once, i.e., phase decomposition. In this study, the distinctive effects of SPD and NPD in surface generation on phase changes of Zn-Al alloy in ultra-precision raster milling (UPRM) with horizontal cutting under up-cutting mode were firstly discussed. At the machined surfaces of Zn-Al alloy, NPD and SPD both results in phase changes, but only NPD changes preferred crystal orientation; and PD under high-speed cutting induces phase changes twice, i.e., four-phase transformation occurs after phase decomposition, namely twin phase changes, which were firstly observed.