Mechanical Characteristics of Zn-22% Al and Al-3% Mg Alloys Processed to High Strains by ECAP

Abstract

A processing route enhancing the strength of a metallic material usually leads to a decrease in the ductility. Therefore, a mechanical processing technique improving the ductility as well as the strength of a structural material is of significant importance. The present study employs equal-channel angular pressing to impart high strains up to ~24 and ~8, via route BC, in Zn-22% Al and Al-3% Mg alloys, respectively. Tensile specimens, machined from the central region of the processed materials, were tested at room temperature between strain rates of 10-3 and 1 s-1. The Zn-22% Al did not show the presence of a critical strain above which high ductility-high strength could be simultaneously achieved at any strain rate. However, Al-3% Mg processed through 8 passes of ECAP showed a transition to a high strength-high ductility region at high strain rates. The occurrence of high strength and high ductility in Al-3% Mg after processing to very high strains is probably due to the transition from the heavily deformed and heterogeneous microstructure present at the lower strains when processing by ECAP to the more homogeneous structures that develop after larger numbers of passes in ECAP. The absence of a transition strain in Zn-22% Al is attributed to its low melting temperature so that even at room temperature (~0.54Tm where Tm is the melting temperature) it shows diffusion-controlled high temperature deformation behavior.