Effect of Temperature on the Subsurface Microstructure and Mechanical Properties of AA 7075-T6 in Machining

Machining processes such as turning are known for generating high strains, strain rates and temperatures. These mechanical and thermal loadings combined on the workpiece can affect the surface microstructure in the context of average grain sizes, texture … etc. Therefore a thorough understanding of these two competing phenomenon on the surface should be investigated to predict the surface microstructure and therefore mechanical properties. However more and more specific parts used in high frequency cyclic loading applications require not only an understanding of the surface but also the subsurface microstructure evolution in the context of deformation resistance and fatigue failure. The main scope of this paper is to investigate the thermal effects of a machining process on the subsurface grain size and hardness through a modelling approach. In this work, a physics-driven model to predict temperature profiles in turning is proposed. Based on the predicted results, a diffusion-based model to predict the average grain size growth in the subsurface is developed, subsequently the Hall-Petch phenomenological equation was used to predict the hardness evolution in the subsurface. To validate the predicted results, machining experiments were conducted for aerospace aluminum alloy AA-7075-T6.