Deformation Behaviors Of Spray Deposited Ultrahigh Strength Al Alloy By ECAP

Two deforming routes at either A or Bc for different passes of Al-11.5%Zn-2%Mg-1.5%Cu-0.2%Sc-0.15%Zr super-strength alloys at 300℃were carried out by equal-channel angular pressing(ECAP). The microstructures of sprayed and deformed samples were investigated by means of Electron backscatter diffraction (EBSD), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Mechanical properties at both room temperature and elevated temperature were measured and the effects of ECAP parameters on mechanical properties at room temperature were analyzed. Relationships among flow stress, strain, strain rate and temperature were established.Dislocation tangle was formed inside grains during ECAP, which evolves to low angle grain boundaries (LAGBs) and further high angle grain boundaries (HAGBs). Therefore, the grains size can be refined significantly. Microstructure analyses show that the grain size was remarkablely refined to less than 900nm by 8 passes Bc ECAP from earlier 3.5μm of sprayed alloy. Different deformation paths leaded to various grain morphologies. The rod-shaped MgZn2 phase was damaged and a few fine Al3(Sc,Zr) were dispersed uniformly after ECAP, which decreases both tensile strength and elongation at room temperature due to occurrence of defects, such as dislocations and minor voids. Texture of the alloy was changed after severe shear deformation.The maximal elongation of 240% was obtained for the alloy through 8 passes A path ECAP at 300℃and strain rate of 5.0×10- 4 s-1 for strain hardening was counteracted by dynamic recovery, exhibiting its better super plasticity. While in case of the alloy through 8 passes Bc path ECAP, the best plasticity of 211% was obtained with high strain rate of 1.0×10 - 2 s-1 due to the balance between dynamic recrystallization and strain rate hardening, in which the strain rate sensitivity exponent was 0.34 and dislocation viscous gliding is considered to be the controlling deformation mechanisms in grain boundaries and inside grains. Fractography at elevated temperature demonstrates that the fractures of the alloys were in either transgranular, intergranular or mixed mode. Cavities formed at the fractured surface of the super plastic deformed samples.