A critical evaluation of the processing of an aluminum 7075 alloy using a combination of ECAP and HPT

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2014-02, Vol.596, p.52-58
• Main Authors: Sabbaghianrad, Shima, Langdon, Terence G.
• Format: Article
• Language: English
• Subjects: Aluminum base alloys; Applied sciences; Cross-disciplinary physics: materials science; rheology; Elasticity. Plasticity; Elongation; Equal channel angular pressing; Exact sciences and technology; Failure; Hardness; High-pressure torsion; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microhardness; Other heat and thermomechanical treatments; Physics; Superplasticity; Treatment of materials and its effects on microstructure and properties; Ultrafine grains; Vickers microhardness
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2013.12.034

Experiments were conducted on a commercial Al-7075 alloy by processing by ECAP for 4 passes and then processing by HPT for up to a maximum of 20 turns. Measurements show that the grains were refined to ~680nm after ECAP and to ~310nm in the center of the disk after ECAP+HPT. Tensile testing at a temperature of 623K revealed lower flow stresses and higher elongations to failure after processing by ECAP+HPT. Thus, the alloy was not superplastic after processing by ECAP but superplasticity was achieved with elongations up to ~800% after processing by ECAP+HPT. By plotting the Vickers microhardness against equivalent strain, it is shown that the hardness saturates at Hv≈250 after ECAP+HPT. This saturation hardness is higher than the value of Hv≈230 recorded after processing by HPT without a preceding step of ECAP. The results demonstrate that processing by ECAP+HPT produces higher hardness and greater grain refinement than processing only by HPT.