Porosity-grain growth relationships in the laser beam deep penetration welding of 6061 aluminum alloy

Porosity is one of the significant defects existing in the weld seam of aluminum alloy by laser. In the current research, the evolution of porosity and grain coupling growth in the weld seam is realized via a Cellular Automaton-Finite Element simulation method. A detailed calculating method of three phases was proposed by taking into account the liquid/solid phase transformation on the nucleation and growth of porosity. The results show that the porosity nuclei with larger size can grow preferentially, while the small porosity nuclei's development is inhibited. Because of the effect of gas/liquid surface tension, porosity increases spherically when it is enveloped by liquid. After touching with grain, the porosity's growth space is restricted by the complex dendrite network, and thus its shape becomes irregular. The coupling of grain and micro-porosities predicted by the simulation method is in good agreement with the results obtained by the experiments.