Microstructural evolution and fracture mechanism of a new Al–Zn–Mg–Cu–Zr alloy processed by equal-channel angular pressing

Equal-channel angular pressing (ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained (UFG) materials. A new Al–Zn–Mg–Cu–Zr alloy was subjected to ECAP experiment in Route B_C (i.e ., rotated 90° in the same sense between each pass). The effect of ECAP on the microstructural evolution and fracture mechanism of the alloy was analyzed by optical microscope (OM), X-ray diffraction (XRD), tensile test (at room temperature), and scanning electron microscope (SEM). The results show that the main strengthening phase of the alloy is MgZn₂, whose content increases apparently after ECAP, the dislocation density increases by one order of magnitude, the hardness value of the 1 pass ECAPed sample increases by 53 %, the ultimate tensile strength (UTS) increases by 29 %, and the true strain increases by 15.4 %. But the further increase in the strength with the passes increasing would cost a slight drop in the true strain. The morphology of the tensile dimples is converted from elongated one to equiaxed one with a uniform distribution of size and depth after pressing.