Porosity and microstructure in pulsed Nd:YAG laser welded Ti6Al4V sheet

The overlapping factor of pulsed laser welding is used to help understand the correlation between welding parameters and the quality of Ti6Al4V welded joints. The number of porosity decreases with the increase in overlapping factor, and the welded joints are almost completely free of porosity when overlapping factor is greater than 75%. This can be attributed to the fact that the remelted volume of the spot region increases with the increase of overlapping factor, which assists porosity formed in the previous pulse wave in escaping from molten pool formed by the subsequent pulse. With the increase of overlapping factor, the weld microstructure becomes much coarser and the width of the fully transformed region of heat affected zone increases, which reduces the microstructure gradient and microhardness gradient from the fusion zone to heat affected zone. A method to evaluate the porosity susceptibility of a specific welding condition prior to actual welding process is presented.