Cryogenic Cutting of AZ31B-O Mg Alloy for Improved Surface Integrity: Part I — Process Principles and Material Modeling

This is Part I of a two-part series numerical study which investigates the improvement of surface integrity of AZ31B-O magnesium (Mg) alloy by cryogenic cutting. A light-weighted material of Mg alloy has great potentials for a more extensive application in transportation/aerospace industries and other areas, such as biodegradable medical implants. However, undesired surface integrity, in terms of grain size, microhardness, residual stresses, limit the functional performance of products with components in these materials on strength, wear resistance, fatigue resistance, and corrosion resistance. In this paper, the principle of improved surface integrity by cryogenic cutting is firstly introduced based on a previous experimental study on cryogenic orthogonal cutting of AZ31B-O Mg alloy. To demonstrate the capability of cryogenic cutting on improvement for AZ31B-O Mg alloy components, the improved surface integrity is characterized in terms of better surface finish, ultrarefined grains, increased surface microhardness, and compressive residual stress. A physics-based constitutive material model of plasticity and grain refinement is developed based on both slip and twinning mechanisms for the AZ31B-O Mg alloy undergoing cryogenic cutting.