Microstructural and nano-composite coating for enhanced durability of laser welded UNS S32304–SS304L joints

This research investigates a surface engineering approach to improve the sustainability, corrosion resistance, and tribological performance of laser-welded dissimilar joints between UNS S32304 duplex stainless steel and SS304L austenitic stainless steel. A Hybrid Aluminium Metal Matrix Composite (HAMMC) coating, developed from AA2024-T351 powder reinforced with 3 wt-% graphite and 3–9 wt-% B₄C, is applied to the weld zone using a two-step method involving ball milling and dip coating. This coating strategy produced a uniform protective layer over the welded region and aimed at enhancing surface integrity, bonding stability, and service life. The coated joints are characterised using microstructural, mechanical, tribological, and electrochemical analyses. The results showed a 38% reduction in interlayer growth, indicating improved weld zone stability. Corrosion performance is also significantly enhanced, with a 40% reduction in corrosion current density and a 72% decrease in corrosion rate, together with improved electrochemical stability (n = 5, p < 0.0055). Tribological testing further demonstrated strong performance gains, including a 70% reduction in specific wear rate and a 46% reduction in coefficient of friction. Microstructural observations confirmed reduced wear damage and improved tribofilm formation on coated surfaces. Overall, the HAMMC coating effectively improved the microstructural stability, corrosion resistance, and wear resistance of the dissimilar stainless-steel joints.