On the interaction of cooling rate with thermal-microstructural-mechanical characteristics of laser-welded α plus β titanium alloy

The joining of thin sheet Ti-6Al-4V alloy has potential application as an encapsulation of miniature components. However, it is quite challenging to achieve a defect-free joint in a fusion welding process since the complexity increases many folds with reduced thickness of the materials. In the present investigation, thin sheet Ti-6Al-4V alloy is welded under different process parameters (26, 45, and 74 J/mm), using a controlled and regulated pulse laser welding technique. The weld joints are further analysed using an experimental and numerical approach to explore the interplay of thermal-microstructural and mechanical characteristics. The outcome of the present investigation reveals better surface quality, desirable microstructural changes, and enhanced joint strength for the joints fabricated under the least heat input condition (26 J/mm). Such overall improvement in the joint characteristics is associated with the high value of cooling rate (2834 K/s), leading to the formation of fine needle-shaped alpha'-martensite, which corresponds to maximum joint efficiency of 90%. Surface finish is another crucial factor that is affected by the amount of heat input. Joints fabricated under low heat input conditions (26 J/mm) exhibits a lower roughness value (R-a similar to 5.67 mu m) as compared to joints fabricated under high heat input conditions (74 J/mm).