Microstructure and properties of 7075 aluminum alloy welding joint using different filler metals

Al-Mg-Sc, Al-Si-Sc and Al-Zn-Mg-Cu-Ti/TiB2 alloy welding wires are prepared to evaluate their weldability toward the high strength 7075 aluminum alloy. The microstructure and the mechanical properties of the welding joints were studied by optical microscope (OM),scanning electron microscope (SEM), transmission electron microscope (TEM), hardness test and tensile test. The results showed that the welding wires of Al-Si-Sc alloy and Al-Zn-Mg-Cu-Ti/TiB2 alloy exhibit good weldability, while that of Al-Mg-Sc alloy is of relatively poor weldability due to the existence of hot cracks. The welding joint using Al-Zn-Mg-Cu-Ti/TiB2 alloy welding wire has the highest ultimate strength of 300 MPa, while the ultimate strength of the welding joints using Al-Mg-Sc and Al-Si-Sc alloy welding wires are 200 MPa and 144 MPa, respectively. The weld zone formed by Al-Zn-Mg-Cu-Ti/TiB2 alloy welding wire consists of fine equiaxed grains with sizes around 15 µm, which are associated with the modification of the Al3Ti and TiB2 particles. The low-cost Al-Zn-Mg-Cu-Ti/TiB2 alloy welding wire has good application potential in the welding of 7000 series ultra-high strength aluminum alloy, due to its excellent weldability and good mechanical properties.