Enhanced surface integrity of AZ31B Mg alloy by cryogenic machining towards improved functional performance of machined components

Abstract

Surface integrity of machined components has a critical impact on their performance. Magnesium alloys are lightweight materials used in the transportation industry and are also emerging as a potential material for biodegradable medical implants. Surface integrity factors, such as grain size, crystallographic orientation and residual stress, have been proved to remarkably influence the functional performance of magnesium alloys, including corrosion/wear resistance and fatigue life. In this study, the influence of dry and cryogenic machining (liquid nitrogen was sprayed on the machined surface during machining) using different cutting edge radius tools on surface integrity was investigated. Compared with the initial material, cryogenic machining when using a large edge radius tool led to enhanced surface integrity in terms of the following: (1) improved surface finish; (2) significant grain refinement from 12μm to 31nm in the featureless surface layer; (3) large intensity of (0002) basal plane on the machined surface; (4) 10 times larger compressive areas in residual stress profiles; these changes should notably improve the functional performance of machined AZ31B Mg alloy. In addition to the frequently reported benefits on tool life, this study suggests that cryogenic machining may also enhance the surface integrity of the workpiece and improve the performance of machined components.