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摘要
Friction stir welding of low Cu and high strength Al-Zn-Mg-Cu alloy plate was carried out at 300 r/min and 900 r/min. The microstructure and mechanical properties of the welded joints were analyzed by means of metallographic microscope, scanning electron microscope, transmission electron microscope, Vickers hardness and tensile test. The results show that there is absence of obvious change of micrometer AlMnCr phase during the welding process, and the dissolution and coarsening occur in intracrystalline nanoscale MgZn2 phase and grain boundary submicron MgZn2 phase. With the increase of welding speed, the degree of precipitate dissolution is increased, and the grain size of welded joint tends to be increased. Under the combined action of grains and precipitates, the hardness of the welded joints of the alloy is characterized by approximate U-shaped distribution. The hardness of the heat affected zone on the advancing side is slightly lower than that on the retreating side, and that of the welding nugget and heat affected zone is relatively low, which is the fracture position of the welded joints, presenting zigzag fracture shape affected by the S line defect. The welded joints of low Cu and high strength Al-Zn-Mg-Cu alloy have the better properties under the low rotational speed of 300 r/min. The maximum tensile strength, yield strength, elongation and welding coefficient reach 393 MPa, 261 MPa, 12% and 80%, respectively. ? 2020, Journal Office of Special Casting and Nonferrous Alloys. All right reserved.
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