Analysis of microstructure and mechanical properties change in laser welding of Ti6Al4V with a multiphysics prediction mode

This paper reports on a study involving examination of the geometry, microstructure and microhardness of welds produced on a 1.625 mm thick Ti6Al4V titanium alloy using the IPG YLR-1000 fiber laser. A numerical model has been developed to predict the fusion zone (FZ), heat affected zone (HAZ) and microhardness of the weld. The thermal history from the multi-physics model is incorporated into a two-dimensional phase prediction model to predict the alpha' martensite formation in the heat-affected zone and fusion zone. The multi-physics phase prediction model is applied to simulate the laser keyhole welding process with varying laser power and welding speed. It was observed that the weld geometry and microhardness predictions from the multi-physics model were in good agreement with the experimental data. The results show that the peak hardness consistently appear at the FZ and HAZ boundaries due to the high cooling rate. In addition, it has been found that laser welding speed has a profound influence on acicular a' martensite formation leading to hardness change. Consequently, to minimize the weld hardening, use of lower power and lower welding speed parameters is recommended in the power range of 800-1000W and welding speed range of 1.73-4 m/min. (C) 2016 Elsevier B.V. All rights reserved.