Abstract: Welding with trailing rotating extrusion (WTRE) is a new technology to improve the microstructure and mechanical properties of welded joints as well as control welding residual stresses and distortion of thin-walled structures. The metallographs of 2A12T4 aluminum alloy welded joints show that the microstructure of the WTRE welds are more compact with refined crystal grains and less welding defects such as air cavities and shrinkage porosities than the ones of the conventional welds.The results of tensile and bending tests show that such mechanical properties as tensile strength and three-point bending strength of the welded joints are enhanced markedly.The cracks in some WTRE test pieces started from the weld center rather than the weld toes, which were strengthened by the rotating extrusion operation.