Development of mechanical properties and microstructure for Al-Zn-Mg-Cu alloys through ECAP after optimizing the outer corner angles through FE modeling

Equal channel angular pressing (ECAP) is an efficient metal forming tool, generally used to improve the mechanical properties by refining the grain structure in metals and alloys. In the present work, both experimental and simulation approaches have been utilized to investigate the deformation behavior of EN AW 7075 alloy during ECAP. The formation and homogeneity of the Von-Mises stress and plastic strain of the samples during ECAP with different outer corner angles (OCAs) have been investigated by the finite element method (FEM). The results revealed that the effective strain was higher and uniform for 10 degrees, 20 degrees, and 30 degrees OCAs die compared to other OCAs. Beyond 30 degrees, the magnitude of strain was found lower with a less homogenous distribution of strain. A sharp plastic deformation zone (PDZ) was noticed for 10 degrees and 20 degrees OCAs, although broadened gradually over an OCA value of 20 degrees. Moreover, lower and uniform Von-Mises stress was generated along the diameter of the sample for the OCA of 20 degrees compared to other OCAs. A gradual reduction of plastic strain has been documented with the enhancement of OCAs along with the sample diameter. The sharpest damage, however, was noticed for the OCA of 90 degrees due to the higher gap between the sample and both die surfaces. Interestingly, the most uniform severe plastic deformation and highest strain homogeneity in terms of inhomogeneity index and coefficient of variance were achieved for 20 degrees and 30 degrees OCAs. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analysis illustrated the formation of ultra-fine grain structures containing very fine eta' and eta precipitates during the post-ECAP process. An improvement in the hardness, yield strength, and ultimate strength by 22%, 18%, and 14%, respectively, after ECAP has been recorded in comparison to the initial artificially aged condition. The improvements in mechanical properties were improvised primarily due to grain refinement combined with precipitate hardening. [GRAPHICS]