Forming mechanisms and mechanical property of AZ31B/2024-T4 friction stir welded T-joints
Tao Sun, Yifu Shen, Fujun Cao, Yinfei Yan, Ruiyang Ni, Jiayi Jin
Abstract
Dissimilar AZ31B/2024-T4 T-lap-joint was successfully fabricated by friction stir welding (FSW) with the rotation speed of 600r/min and the welding speed of 65 mm/min. The microstructure characteristics were observed and analyzed with optical microscope (OM) and the forming mechanisms were discussed by energy spectrometer (EDS) and X-ray diffractometer (XRD). In addition, the effect of microstructure on mechanical properties was analyzed. The results showed that the metal of the skin and stringer are fully mixed at the original connection surface under the action of stirring and friction of the pin. The welded joint formed a mixed region of magnesium and aluminum (Mg–Al MR). A multiphase structure composed of α-Al, α-Mg, and Al12Mg17 was formed in Mg–Al MR, which also contained a small amount of Al3Mg2. The microhardness values were W-shaped and N-shaped along the skin and stringer directions, respectively. The microhardness values in MR rose rapidly and the broken Mg matrix in the skin was evenly distributed in the MR. The tensile results showed that the skin have excellent failure strength, which was 85.2% of the base metal. The fracture morphology of skin and stringer was mixed fracture and brittle fracture, respectively.