Research On Friction Stir Spot Welding Process Of Dissimilar Aluminum To Steel For Car

With the development of lightweight vehicle,more and more automotive companies have begun to study the use of lightweight materials or composite materials to replace traditional materials in autobody panel for lightweighted vehicles.And the jointing between aluminum and steel has become a research hotspot.Due to the superiority of Friction Stir Spot Welding?FSSW?in the welding of lightweight aluminum alloy materials,it has become a superior jointing method of aluminum and steel.In this paper,joints were produced by overlapping 1.2 mm thick 6061aluminum alloy to 1.2 mm thick B240VK steel using FSSW.Orthogonal experiment was carried out with two different pin-length tools,and the influence of different process parameters on the tensile mechanical properties of the FSSW joints was studied.The experimental results show that the use of the 1.5 mm pin-length tool has significantly better tensile mechanical properties than using the 1.3 mm pin-length tool.With the 1.5mm pin-length tool,A maximum value of 3.5 kN in the tensile shear strength was obtained when rotation speed equals to 1000 r/min,plunge depth equals to 1.8 mm,dwell time equals to 10 seconds,and plunge insert speed equals to 10 mm/min.The mechanical properties of FSSW joints are mainly influenced by three factors of the state of the intermetallic compound layer,the formation of the hook and the effective thickNess of the upper plate.The scanning electron microscopy?SEM?results of FSSW joints show that there is a clear intermetallic compounds?IMC?layer near the hook,and its thickNess is positively correlated to the heat input.The phase composition of Al₁₃Fe₄and Fe₂Al₅ was determined by XRD and EDS.With the increase of the plunge depth,the hook area increases,but the shear strength of the FSSW joints decreases.With the increase of the plunge depth,the effective thickness of the upper plate decreases,and the shear strength of the FSSW joints also decreases.Micro-hardness test results show that the hardness of the stirring zone in the lower steel plate increases with the increase of the welding depth.The microscopic appearance of the fracture presents a river-like cleavage step pattern,which indicates that the fractured form of the FSSW joints exhibits cleavage fracture microscopically and brittle fracture macroscopically.