Study on Backward Extrusion of Large-Sized and Hollow Cup Using High-Strength Al-Zn-Mg-Cu Alloy

The large-sized and hollow Al-Zn-Mg-Cu cup was produced through backward extrusion process. The effects of billet temperature on the microstructure, mechanical properties and corrosion resistance along both extrusion direction (ED) and transverse direction (TD) were investigated based on numerical and experimental works. It was found that as the billet temperature increases, the extrusion load decreases significantly and the equivalent strain increases. The bimodal structure consisting of elongated and fine grains formed because of the occurrence of slight DRX. A high billet temperature relieved the elongation of grains, increased the fraction of recrystallization texture, and activated the grain growth. And a large number of second phases of MgZn 2 , Al 7 Cu 2 Fe, and Al 2 CuMg were found in the extruded cup. At the same time as the billet temperature increases, the size of Al 7 Cu 2 Fe decreases and the amount of fine MgZn 2 increases. The highest ultimate tensile strength of 400.6 MPa along ED and 391.0 MPa along TD was achieved with the high temperature of 450 °C. The elongation along ED was stable, while that along TD was always lower and showed an increasing trend with the increase in billet temperature. The intergranular corrosion resistance along ED changed slightly. For TD samples, the corrosion depth reached 232 μm with billet temperature of 350 °C, while it was only 90 μm with increasing the temperature to 450 °C. Graphical Abstract