Experimental investigations and process optimisation of the submerged waterjet peening process on AZ31B Mg alloy for biomedical applications

Abstract

This research investigates the surface treatment of AZ31B magnesium alloy using submerged waterjet peening in order to improve its mechanical properties and biocompatibility for biomedical applications. The experimental parameter conditions were set by varying jet pressure (P) from 100 MPa to 150 MPa and traverse speed (v) from 60 mm/min to 240 mm/min, with a constant standoff distance (h) of 1.5 mm at a single pass. Their effects on surface hardness and roughness were investigated. Results showed that surface roughness increased significantly at lower traverse speeds due to prolonged jet interaction, while hardness improved by up to 26.06% owing to dislocation density and grain refinement. Multi-objective optimisation using the TOPSIS method identified an optimal parameter combination of 150 MPa pressure, 120 mm/min traverse speed, and 1.5 mm standoff distance, balancing roughness and hardness. Validation by Random Forest Regression with Leave One Out Cross Validation ensured model accuracy. Surface morphology exhibited erosion-induced craters and pits because of cavitation-driven plasticity, and XRD analysis confirmed no phase transformation but an increase in dislocation density. Topographical and wettability measurements indicated increased surface energy and decreased contact angle, favoured by greater asperity density. Biocompatibility tests proved enhanced MG-63 cell viability and adhesion on peened surfaces, which verified the bio-functionality of the alloy surface modification. The results establish submerged waterjet peening as a promising, non-thermal surface treatment for AZ31B alloy surface modification for load-bearing implant applications.