EFFECT OF THE BIMODAL STRUCTURE PROCESSED BY ECAP AND SUBSEQUENT ROLLING ON STATIC STRENGTH AND SUPERPLASTICITY OF Al-Mg-Sc-Zr ALLOY

Abstract

Microstructure and mechanical properties of the 1570C aluminum alloy were studied after equal channel angular pressing (ECAP) to the strain of 3 at 325°C and subsequent warm and cold rolling with near 80% reductions at 325°C and 20°C, respectively. Even containing a partially recrystallized bimodal structure with a volume fraction of ultrafine grains of 0.3 and their size not exceeding 2 mm, the alloy after ECAP demonstrated an excellent balance of room temperature static strength parameters (yield strength (YS) » 300 MPa, tensile strength (UTS) » 400 MPa and elongation (El) » 26%), and high strain rate superplasticity (with maximum elongation exceeding 2500% at 520°C and a strain rate of 1.4 × 10-2 s- 1). Subsequent warm and cold rolling resulted in an increase in YS to 340 and 430 MPa and UTS to 415 and 485 MPa amid El decreased to 24 and 11%, respectively. Despite the difference in the deformation structures formed in both rolling states, similar superplastic behavior was observed with maximum elongations of up to 3000% at temperatures of 500-520°C and strain rates of about 10-2 s-1. It was concluded that the initial processing of the alloy to relatively low ECAP strains before warm/cold rolling, leading to bimodal structure with a low fraction of ultrafine grains, is sufficient to ensure a favorable combination of both service and technological properties of the sheets obtained.