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A joint of titanium and transparent polyamide with desirable strength was achieved by laser joining. A maximum load capacity of 3400 N was obtained from a lap joining area of 25 × 25 mm2 at a laser power of 350 W and a travel speed of 4 mm/s. The effects of surface oxide layers with different thicknesses and stability were investigated. A joint with a thick oxide layer exhibited lower load capacity due to excessive thermal degradation of polyamide caused by heat buildup inside the thick thermal insulating oxide layer. With UV exposure, more pronounced reduction in joint strength was observed in the joint with the thick oxide layer. Cracking of the oxide layers was responsible for lower strength and expected to be a result of stress from polyamide contraction combining with internal stress of the oxide layer.

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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.