Electrically-Assisted Friction Stir Welding of Aluminum Alloy to Advanced High Strength Steel.

Friction Stir Welding;Dissimilar Materials;Electro-Plastic Effect;Electrically Assisted Process;Experiment;Thermo-Mechanical Modeling;Mechanical Engineering;Engineering;Mechanical Engineering

Liu, XunKannatey-Asibu(jr), Elijah ;

University of Michigan

关键词: Friction Stir Welding;    Dissimilar Materials;    Electro-Plastic Effect;    Electrically Assisted Process;    Experiment;    Thermo-Mechanical Modeling;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/133252/xunxliu_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Growing concerns on energy consumption increase the demand of lightweight vehicles. One of the most efficient solutions is to use multi-material structure. As a solid state process, friction stir welding (FSW) is promising for joining dissimilar materials. However, the processing window for achieving successful dissimilar joints is still narrow. Besides, a large axial welding force is required when steel is involved. In order to address these challenges, a material softening phenomenon, electro-plastic effect (EPE) is proposed to be incorporated into the process. In this research, first, EPE on various materials is systematically reviewed and a hypothesis is proposed for understanding the softening mechanisms. The effectiveness of EPE is then evaluated on one type of advanced high strength steel, TRIP 780/800 steel.Second, traditional FSW process is experimentally studied for joining dissimilar Al 6061 to TRIP steel. Effects of process parameters on joint microstructure evolution are analyzed based on the mechanical welding force and temperature measured during the process. Intermetallic compound (IMC) layer of FeAl or Fe3Al with thickness of less than 1 μm is formed at the Al–Fe interface in the advancing side. The maximum ultimate tensile strength can reach 85% of the base aluminum alloy. Third, analytical and numerical models are developed for friction stir welding of dissimilar materials. For plunge stage modeling, the field variable is introduced to identify regions of steel and aluminum and define the generalized material properties. Conservation equations are separately developed at the two materials interface for the discontinuities. The stable welding stage is modeled based on Eulerian formulation using multiple phase flow theories. The developed model can capture the material and temperature distribution measured from experiments.Finally, high density electrical currents are applied to the FSW process. Plunge stage of FSW is studied on aluminum alloy Al 6061 and TRIP 780 steel respectively. Effective reduction of the axial welding force can be obtained with good repeatability. During the FSW of Al 6061 to TRIP steel, the axial welding force can be consistently reduced under various welding conditions, which is a synergic result of both electro-plastic effect and Joule heating.