Evaluation of the microstructure and mechanical properties of additive manufactured Ti-6Al-4V alloy under various heat treatment conditions: Optimization of heat treatment programme and depth of effective layer

This study used selective laser melting (SLM) technology to fabricate Ti-6Al-4V titanium alloys, which were subsequently subjected to heat treatment under a range of parameters. The investigation focused on the microstructure, microhardness, phase composition, tensile properties, and fracture surface morphology of the optimized SLM-fabricated Ti-6Al-4V specimens, to explore the mechanical properties and effective strengthening depth of these specimens. The results indicate that the grains of the SLM-fabricated Ti-6Al-4V specimens are slender and needle-shaped. As the heat treatment temperature increases or the cooling rate decreases, the grain structure becomes coarser and shorter. Additionally, the heat treatment temperatures and cooling rates significantly affect the yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of the SLM-fabricated Ti-6Al-4V samples. Among them, the sample after 850℃-WQ heat treatment obtained higher plasticity (304.92 % EL) and better overall performance at the cost of a small strength (4.96 % UTS and 6.08 % YS). This specific heat treatment effectively improves the mechanical properties of SLM-formed parts with a thickness of 50 mm. These results offer a promising strategy for the cost-effective enhancement of the mechanical properties of SLM-fabricated Ti-6Al-4V parts in larger thicknesses.