Effect of plate thickness on weld pool dynamics and keyhole-induced porosity formation in laser welding of Al alloy

A three-dimensional (3D) transient numerical model is developed to simulate the keyhole dynamics, melt flow, and keyhole-induced porosity formation. The influence of the plate thickness on keyhole-induced porosity size and number is thoroughly investigated. The simulation results show that the average keyhole depth in plate thickness of 3, 6, and 10 mm is 2.07 mm, 1.89 mm, and 1.77 mm, respectively, and the value of keyhole depth reaching the quasi-steady state is 34 ms, 28 ms, and 14 ms, respectively. Compared to the thinner thickness plate, it is not easy to see the phenomenon of bubble amalgamation in the thickness of 10 mm under the parameter of low laser power and high welding speed. The less porosity in thicker plate laser welding is attributed to lower frequency of keyhole collapse, higher ratio of keyhole open after keyhole collapse to total keyhole collapse number, lower ratio of bubble number to total keyhole collapse number, higher ratio of bubble escape to the total bubbles number, and lower ratio of bubble amalgamation to the total.