Guofu Xu

Mechanical Properties, Corrosion Behavior, and Microstructures of a MIG-Welded 7020 Al Alloy

Abstract7020 aluminum alloy plates were welded by metal inert gas welding method, with the ER5183 welding wire containing Zr and ER5356 welding wire without Zr, respectively. The mechanical properties, corrosion behavior, and microstructures of these two welded joints were investigated. The tensile strength and ductilities of the joints are inferior to those of base alloy, and the lowest hardness is obtained in the welded zone, while the heat-affected zones are more sensitive to corrosion than the base metal and welded zones. The base metal shows a deformed subgrains microstructure, and the heat-affected zones still remain in elongated shape, where the soften zones form as a result of η′ (MgZn2) coarsening. Two welded zones are mainly characterized by as-cast structure; however, grains are refined and a zone of equiaxed grains forms along the bonding boundary due to the Zr addition into ER5183 Al alloy. Accordingly, the mechanical properties and corrosion resistance in this zone of the joint with ER5183 exhibit better than those of the joint with ER5356.

Research on constitutive models and hot workability of as-homogenized Al-Zn-Mg-Cu alloy during isothermal compression

Hot compression tests of as-homogenized Al-Zn-Mg-Cu alloy were performed at the deformation temperature range of 350-450 °C and the strain rate range of 0.001-1 s-1. The Arrhenius-type constitutive equation and the Avrami-type model were established to predict the flow behaviors of the alloy respectively. The processing map at the true strain of 0.92 was developed to evaluate the workability of the alloy and the related microstructures were investigated. The results show that the Avrami-type model has a higher accuracy to predict flow stress than the Arrhenius-type constitutive equation. The stable deformation occurs under high temperature or low strain rate mainly owing to the dynamic recrystallization. Flow instability is prone to occur under the condition of low temperature and high strain rate due to the initiation and the propagation of micro-cracks. According to the processing map and corresponding microstructure characteristics, the optimum processing parameters are in the temperature range of 380-405 °C and the strain rate range of 0.006-0.035 s-1.