Weld diffusion analysis of forming bimetallic components using statistical experimental methods

Bimetallic components made of aluminium alloy and stainless steel can provide the benefits of light weight and excellent wear resistance. Most literature indicates that good bonding of such dissimilar metals can be achieved by friction welding and diffusion welding. However, poor adaptability to component shapes and long processing time limited their applications. If a large amount of deformation is permitted, hot-pressure welding (HPW) and forge welding (FOW) are more efficient for forming arbitrary shapes of bimetallic components. In order to ensure a successful weld, the diffusion of elements between two metals should be analyzed because this is significant for evaluating the effectiveness and weld quality of those solid-state welding processes. The study described in this article describes a diffusion analysis of forming bimetallic components under HPW and FOW processes, which were performed at various welding temperatures T and forming deformation F. 6063 aluminium alloy and AISI 316L stainless steel were selected as the specimen materials. The good-quality bimetallic components were obtained by FOW at T=450C and F=8mm. Their welds exhibited an average tensile strength of 111.29MPa. Using scanning electron microscopy as a tool for metallographic analysis, a full 4m thick diffusion layer was found in the weld interface. According to the results of the energy-dispersive X-ray spectroscopy and X-ray diffraction analysis, this layer consisted of several intermetallic compounds such as FeAl3, Fe2Al5, Fe3Al, Al5Fe2, Al13Fe4, and AlFe, which achieved the bonding between aluminium and iron elements. Weld discontinuities existed in the diffusion zone of all HPW components that weakened the overall strengths of their welds. The main cause was recognized to be the temperature drop of the materials that interrupted their coalescence during diffusion. Results were interpreted by statistical experimental methods, which made use of the control charts to analyze the central tendency and spread on the tensile strengths of bimetallic welds produced by both HPW and FOW processes and examine their reliability as well. The present study not only demonstrates that the bimetallic components produced by the FOW are superior in quality and comparable to those reported in previous studies, but also confirms that they are more reliable than the HPW.