An Investigation of Thermal Mismatch Stress Assisted Void Nucleation in Welded Al Alloy Joints

Based on simulated space thermal cycling tests, the mechanical properties degradation and damage mechanism of 5A06 aluminum alloy welded joint were investigated. The mechanical performances were measured and compared before and after thermal cycling process. The microstructure and fracture surfaces were characterized by optical microscope and scanning electron microscopy. Results reveal that thermal cycling can cause performances degradation in the welded joint. Cavity formation can be observed by matrix/particle decohesion during the thermal cycling process. Micro voids nucleation and evolution characterize the internal damage of the welded joint. The dimension and the number of cavities increases during the thermal cycling tests. The thermal mismatch stress between the particles and base alloy can assist the external stress to cause debonding. The simulation of void nucleation in a unit cell model was carried out by FEM. The contributions of the thermal mismatch stress to void nucleation has been studied and introduced to Gurson void nucleation model.