Investigations on high-power laser beam welding of adapters for joining steel and aluminum for thick-walled applications in shipbuilding

In shipbuilding, thick dissimilar joints of steel and aluminum are in great demand to reduce the weight and the center of gravity of the ship. On the one hand, the dissimilar joints lead to a reduction in CO2-emissions as result of lower fuel consumption and on the other hand to a higher ship stability. The joining process used for manufacturing ships employs an explosive welded adapter to join both dissimilar parts. However, the production of these adapters is complex, time-consuming, and costly. Furthermore, these adapters have an oversized thickness, depending on the material thickness of the steel and the aluminum alloy, in order to achieve the required seam strength. There is a high interest for an efficient alternative. In this study, high-power laser beam welding processes are developed for joining steel S355 (thickness t = 5 mm) with aluminum alloy AA6082 (t = 12 mm) in lap configuration with two intersecting laser beams and additional material to increase weld seam quality. Within this framework, two laser beam sources with a max. output power of PL = 6 kW are used to weld dissimilar joints with additional material filled groove. In the course of the welding process development, the influence of the parameters regarding the groove depth on the metallurgical and mechanical properties is investigated. Adequate process parameters are transferred to laser beam welding of adapters. The adapters are characterized, for example, by using metallographic analysis as well as tensile tests under symmetrical and asymmetrical loading. A result is that the adapters reach a max. tensile force of approximately 35 kN and the break occurs outside of the dissimilar joints. The results increase the application potential of laser beam welded dissimilar joints in the field of shipbuilding.