Istraživanje tehnologija spajanja limova od čelika DP500 i legure aluminijuma AW-5754 u cilju razvoja lakih konstrukcija

Abstract

Multi-material design is a key approach in the development of light constructions. Among the major problems in the application of multi-material design is the joining of dissimilar materials, especially steel and aluminum. In this doctoral dissertation, the possibility of joining dual-phase DP500 steel and AW 5754 aluminum alloy is analyzed. These two materials were selected as adequate representatives of the multi-material structure, which is primarily applied in the automotive industry. Generally, this doctoral dissertation consists of theoretical and experimental research. In the part related to theoretical research, the "state of the art" related to the joining of dissimilar materials with an emphasis on the joining of dual-phase steels and aluminum alloys are analyzed. The experimental research in this dissertation is divided into four parts. The first part of the experimental research presents the research of mechanical characteristics, microstructure and macrostructure of the two DP500 steel sheets joint, which is welded by Resistance spot welding. (RSW). Also, this part of the doctoral dissertation analyzes the influence of welding parameters on the mechanical characteristics of the joint, i.e., the optimization of welding parameters using methods such as multiobjective Taguchi optimization and multiobjective Grey-based Taguchi method was done. The second part of the experimental research refers to the research of mechanical characteristics, microstructure and macrostructure of the weld joint of DP500 steel and aluminum alloy AW 5754 obtained by conventional Resistance spot welding (RSW). The third part of the experimental research presents the research of mechanical characteristics, macrostructure and microstructure of DP500 steel sheet and AW 5754 aluminum alloy joint obtained by Resistance element welding (REW), as an alternative to RSW joining technology. Also, the influence of welding parameters primarily on the failure mode, and then on the mechanical characteristics, microstructure and macrostructure of the REW joint were analyzed. Mechanical clinching (MC) is another alternative technique for joining sheets, but without an additional element and without introducing heat. This method of cold forming has performed by the process of local deformations with the punch and die. The fourth part of the doctoral dissertation presents an analysis of the mechanical characteristics and macrostructure of the DP500 steel and the AW 5754 aluminum alloy joint obtained by mechanical clinching. Based on the obtained and presented research results, a ranking of joining technology for dissimilar materials was made. The advantages and disadvantages of the considered technologies were also presented.