Predictive model and analysis of the resultant force in the dry machining of Mg-4Zn/Si3N4 nanocomposites

In aerospace and automotive applications, the usage of magnesium (Mg)-based alloys and composites reduces the structural weight due to their low density. They also possess good specific strength and are abundantly available. The Mg-4Zn alloy is one such Mg-based alloy that is also biodegradable and biocompatible. In spite of these advantages, there is a strong need and scope to improve its wear resistance and mechanical properties. Mg-4Zn nanocomposites with Si3N4 reinforcements (also a biocompatible bio-ceramic) are hypothesized to possess superior properties. Sustainable machining with minimal subsurface defects and minimal energy consumption is necessary to manufacture components from these vacuum stir-cast nanocomposites. The resultant machining force (Fr) is a good indicator of subsurface quality and energy consumption in machining. The addition of Si3N4 reinforcement to improve the properties of the Mg-4Zn alloy could introduce challenges in machining and could influence Fr. To investigate the effect of reinforcement wt.% and machining parameters on Fr and to develop a predictive model for Fr, dry turning experiments on the vacuum stir-cast Mg-4Zn/Si3N4 nanocomposites were carried out based on response surface methodology-based Box-Behnken design. It is observed that Fr is influenced by the reinforcement wt.%, cutting speed, feed rate, and depth of cut and also their squares and their mutual interactions. Variation in porosity, thermal softening, and strain hardening contribute to the variation in Fr. Minimal Fr and hence better subsurface quality and lower energy consumption are obtained at mid values of Si3N4 reinforcement wt.% and cutting speed and low values of feed rate and depth of cut. A grain refinement of 63.94% and a consequent increase in microhardness of 38.67% caused by the Si3N4 reinforcement additions have influenced Fr, as confirmed by the predictive model.