Effect Of ECAP On Microstructure And Mechanical Properties Of A New Al-Zn-Mg-Cu Alloy

With the high specific strength, hardness, toughness and excellent corrosion resistance, Al-Zn-Mg-Cu alloys have become very important structural material not only in aerospace field but also in the fields of the military equipment, nuclear industry, naval vessels and bridges. At present, the aerospace vehicles whose direction of development is high safety factor, low structural weight coefficient and high speed has put forward higher requirements to the structural material. Under the application prospects, in-depth research on the microstructure control, strengthening mechanism, composition optimization and corrosion resistance of some newly developed Al-Zn-Mg-Cu alloys is in urgent need. Equal Channel Angular Pressing (ECAP) is considered to be one of the most effective and basic representative severe plastic deformation technology to produce excellent UFG materials by introducing a large number of high-energy non equilibrium large angle grain boundaries, improving the strength of the boundary and refining the grains.A new Al-Zn-Mg-Cu alloy was subjected to ECAP experiment of different process parameters in Route BC after studying the deformation process by Deform-3D software. The effect of ECAP on the microstructural evolution, mechanical properties and fracture mechanism of the alloy was analyzed by Optical Microscope (OM), X-Ray Diffraction (XRD), Micro Hardness Tester, Tensile Test (at room temperature) and Scanning Electron Microscope (SEM) and so on. The results show that the crystallite size obviously decreases with the pass number, being 79.1 nm for initial sample, and 36.9 nm for the 4th pass one. While the dislocation density was increased by one order of magnitude from 4.90E+13 m"2 to 1.32E+14 m-2. The hardness value of the first pass ECAPed sample increases by 53%. And by increasing passes of ECAP, the value continues to increase, while the rate of increase decreases. Studies show both the strength and the ductility of the material can be simultaneously improved by ECAP in a certain range, but the further increase of the former with the increasing passes would cost a slight drop in the latter.