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

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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 BC (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.