Influence of welding and heat treatment on microstructure and mechanical properties of titanium alloys for marine applications

Abstract

Welding of high-strength titanium alloys, particularly Ti-6Al-4V, poses significant challenges in marine engineering and shipbuilding due to the formation of heterogeneous microstructures and anisotropic mechanical properties. This study investigates the combined effects of welding energy, welding speed, and post-weld heat treatment (PWHT) on the microstructural evolution and mechanical performance of Ti-6Al-4V welds. Cross-sectional metallography, scanning electron microscopy (SEM), and stress–strain analysis were used to evaluate the weld zone, heat-affected zone, and base metal, as well as for quantitative assessment of yield strength, plasticity, and strain distribution. Results indicate that high welding energy and rapid cooling promote coarse martensitic α′ formation in the fusion zone, increasing initial strength but reducing ductility. PWHT transforms α′ into lamellar α+β, narrows the heataffected zone, and enhances microstructural uniformity. Mechanical testing results demonstrate that the solution-treated and aged (STA) condition provides a balanced combination of strength (~925–960 MPa) and ductility, with elongation increasing by 20–30% compared to the as-welded samples. Welding speed primarily determines initial microstructural features, whereas PWHT governs plasticity recovery and fatigue resistance. The study provides the first integrative analysis linking welding parameters, PWHT, microstructural evolution, and mechanical performance in Ti-6Al-4V for marine applications. The findings offer practical guidance for optimizing welding and heat treatment to ensure reliable strength, ductility, and service life of titanium components in shipbuilding and offshore structures. Future research should focus on fatigue behaviour, residual stress management, and integration with additive manufacturing techniques to enhance microstructural control in welded titanium assemblies.