Effect of rotation speed on microstructure and properties of 2024-T4 aluminum alloy submerged friction stir weld

2024-T4 aluminum alloy plate was jointed by submerged friction stir welding (SFSW). The effects of rotation speed on the welding temperature fields of SFS weld, precipitate morphology of the nugget zone and mechanical properties of SFS weld were investigated. The results show that the cooling water circulation medium has significant instantaneous cooling effect; the peak value of welding temperature fields increases from 271.0°C to 310.8°C with the rotation speed increases from 600 r/min to 1180 r/min. The precipitate phases of the nugget zone precipitate and grow under welding thermal cycle. The quantity and size of the precipitates gradually increase with the increase of the rotation speed. The average value of microhardness in the nugget zone of SFS weld decreases from 117.5HV to 99.2HV with the increase of the rotation speed, meanwhile, tensile strength and elongation of SFS weld decrease from 403.3 MPa and 3.24% to 334.5 MPa and 1.44%, respectively.