Investigation of synergistic effect of multidirectional forging and laser shock peening on Mg–Zn–Sn based implant materials

This study investigates the combined effect of multidirectional forging (MDF) and laser shock peening (LSP) on the microstructural evolution, mechanical performance, corrosion behavior, and cytocompatibility of a Mg–4Zn–0.75Sn alloy aimed for temporary orthopedic implant applications. The alloy was subjected to MDF passes, followed by selective LSP treatment on the optimally forged (five-pass) condition. Progressive MDF significantly refined the initial average grain size from 172 ± 12 μm to 22 ± 5 μm, indicating an 87% reduction, with ultrafine grains (5–11 μm) formed after five passes. Subsequent LSP processing further enhanced grain refinement to an average size of 3 ± 0.5 μm. The alloy exhibited substantial improvement in microhardness from 51.8 ± 2 Hv (homogenized) to 92.8 ± 4 Hv (MDF-5P), accompanied by a rise in ultimate tensile strength from 86.99 MPa to 215.13 MPa. The MDF-5P+LSP sample exhibited a gradient nano-hardness profile (0.28–0.20 GPa) and compressive residual stresses up to −29.5 ± 2.5 MPa near the surface. Electrochemical corrosion tests carried out in Hanks balanced salt solution demonstrated remarkable improvement in corrosion resistance, with corrosion rate decreasing from 4.8807 mm·yr⁻¹ (homogenized) to 1.0684 mm·yr⁻¹ (MDF-5P), and further down to 0.3562 mm·yr⁻¹ after LSP. Cytocompatibility assessments using MG-63 osteoblast-like cells revealed superior cell proliferation (111.42 ± 1.11%) for MDF-5P + LSP samples compared to the control. The present work aligns with the SDG 3 -by advancing biodegradable magnesium-based implant materials that promote safer and more effective bone healing.