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

Ghosh Abhishek, Das Kalyan, Eivani Ali Reza, Mohammadi Hossein, Vafaeenezhad Hossein, Murmu Uttam Kumar, Jafarian Hamid Reza, Ghosh Manojit

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 2

art. no. e78, 2023

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°, 20°, and 30° OCAs die compared to other OCAs. Beyond 30°, the magnitude of strain was found lower with a less homogenous distribution of strain. A sharp plastic deformation zone (PDZ) was noticed for 10° and 20° OCAs, although broadened gradually over an OCA value of 20°. Moreover, lower and uniform Von-Mises stress was generated along the diameter of the sample for the OCA of 20° 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° 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° and 30° OCAs. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analysis illustrated the formation of ultra-fine grain structures containing very fine η´ and η 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.

Development of ultrafine grained Al–Zn–Mg–Cu alloy by equal channel angular pressing: microstructure, texture and mechanical properties

Ghosh Abhishek, Ghosh Manojit, Gudimetla Kondaiah, Kalsar Rajib, Kestens Leo A. I., Kondaveeti Chandra Sekhar, Pugazhendhi Bhagat Singh, Ravisankar Balasubramanian

Archives of Civil and Mechanical Engineering

2020

Vol. 20, no. 1

82--98

In this article, an effort has been made to investigate the evolution of microstructure, texture and mechanical properties of AA 7075 alloy during equal channel angular pressing (ECAP) by route BC at room temperature at a pressing speed of 1 mm/min. Transmission electron microscopy (TEM) revealed the presence of rod-like (MgZn2) precipitates in annealed conditions which were broken after two ECAP passes along with remarkable grain refinement due to high imposed strain after the second pass. After two consecutive ECAP passes, hardness, yield strength, and tensile strength of the alloy increased significantly in comparison to initial annealed condition. The fraction of high angle boundaries (HABs) and grain misorientation angle significantly increased after ECAP passes compared to the initial condition. Texture measurements were performed by X-ray diffractometer (XRD), on TD plane (parallel to extrusion direction). Texture results revealed the dominance of Cθ and A∗2θ components after the first pass and the presence of strong Bθ, B¯θ and A¯θ components along with weaker A∗2θ,Cθ components after the second pass. Scanning electron microscopy (SEM) revealed that the average dimple size was gradually reduced with increasing the ECAP passes.