Microstructure and mechanical properties of heat affected zone in multi-pass GMA welded Al-Zn-Mg-Cu alloy
(1. Shandong Provincial Key Laboratory of Special Welding Technology,
Harbin Institute of Technology at Weihai, Weihai 264209, China;
2. National Key Laboratory of Remanufacturing, Beijing 100072, China;
3. State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China)
Harbin Institute of Technology at Weihai, Weihai 264209, China;
2. National Key Laboratory of Remanufacturing, Beijing 100072, China;
3. State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China)
Abstract: Microstructure and mechanical properties of the heat affected zone (HAZ) in multi-pass gas metal arc (GMA) welded Al-Zn-Mg-Cu alloy plates were investigated, based upon which the mechanical anisotropy and fracture mechanism were analyzed. The microstructure and composition were analyzed by scanning electron microscope (SEM) and energy dispersive spectroscope (EDS). X-ray diffractometer (XRD), transmission electron microscope (TEM) and selective area electron diffraction (SAED) were used to analyze the phase composition. The distribution of microhardness was identified as gradual transition and tensile strength had a tendency to decrease first and then increase. The distribution of nano-sized η(MgZn2) particles in the α(Al) matrix and Al2MgCu phase determined the tensile performances along the thickness direction and led to the formation of ductile/brittle composite fracture in the HAZ. The continuous distribution of Al2MgCu phase in the strip intergranular precipitates gave birth to premature cracks and the brittle fracture region. The precipitated particles coarsening also led to the deterioration of mechanical properties.
Key words: Al-Zn-Mg-Cu alloy; heat affected zone; microstructure; mechanical properties; ductile/brittle composite fracture