The Mechanical Properties and Residual Stress of Ultrasonic Nano-crystal Surface Modified Friction Stir Welded Al 2024 T3- Al 7075 T6

摘要

Plates of 5 mm thick of aluminum alloys 2024 T3 and 7075 T6 were joined in a butt joint by friction stir welding (FSW). UNSM technology was applied on the surface of friction stir welded Al 2024 T3-Al 7075 T6 with ceramic ball as pin head. The before and after UNSM treated residual stresses were measured through the surface of FSWed Al 2024 T3-A1 7075 T6 specimen using X-Ray diffraction in the vertical direction of the welding joint. Also, surface roughness and hardness were investigated. The stresses in the test specimen peaked at only +21.9 Mpa and had the conventional "M" profile with tensile stress peak in the heat affected zone of Al 2024 T3 outside the weld zone. In the residual stresses of the treated Al 2024 T3- Al 7075 T6, the original "M" shape profile had been replaced by a uniformly shaped profile and the average residual stresses is about -140Mpa. The tensile properties and micro-Vickers hardness were also measured, both the weakest data of the tensile properties and hardness was located at the heat affected zone of Al 2024 T3.