Experimental investigations and FE modeling considering microstructural inhomogeneity of laser welded steel-aluminum joints

Progresses in fusion joining between aluminum alloys with steel were limited due to its complex metallurgical reactions between liquid steel and aluminum. This work provided an insight into effects of homogeneous and inhomogeneous fusion zone of laser welded steel-aluminum joints. Detailed metallographic and chemical composition analyses of the fusion zone were first presented and discussed. An indentation reverse method was developed for predicting local stress–strain behaviors of the fusion zones. Then, FE simulations of lap shear test for laser welded steel-aluminum joint were performed, in which individual properties of the weld zone were given. The cohesive zone model (CZM) based on maximum strength was applied for representing local damage evolution of intermetallic layer along the interface in welded samples. Cross tension and double cantilever beam (DCB) tests were conducted for determining mode I bonding strength and fracture energy of the CZM. The peak forces of welded steel-aluminum joint samples using different welding speeds were predicted. The numerical results showed satisfactory agreement with experimentally obtained values. In addition, fracture behaviors of different welded samples were evaluated with regard to developed microstructural characteristics. It was found that the dominant local failure mechanism of laser welded steel-aluminum joints was strongly governed by the inhomogeneity of chemical and mechanical properties of their fusion zones that could be precisely described by the proposed model.