Enhancing the strength and ductility in an Al–5Mg alloy via accumulative continuous extrusion forming at room and cryogenic temperatures

Abstract

In this work, the microstructural evolution of Al–5Mg (wt%) alloy fabricated by accumulative continuous extrusion forming (ACEF) at room temperature (RT) and cryogenic temperature (CT) was investigated. The grain refinement mechanism during ACEF was revealed. The strengthen and ductility enhancements of the alloy were discussed. The results showed that good grain refinement effect was achieved in the alloy after multi-pass RT-ACEF, and was further enhanced in the alloy fabricated by 1 pass CT-ACEF. High-density dislocations, as the driven force of continuous dynamic recrystallization, were achieved in the 1 pass CT-ACEFed alloy, and the growth of recrystallized grains was limited at CT. As a result, superior grain refinement effect was obtained in the alloy after CT-ACEF. Simultaneous strength and ductility improvements were found in the ACEFed alloy. The ultimate tensile strength and elongation were enhanced to 294.3 MPa and 55.1 % of the alloy after 1 pass CT-ACEF. Grain boundary strengthening and dislocation strengthening dominated the strength enhancement of the ACEFed alloy. The high work hardening exponent and wide strain interval were responsible for the increase in ductility of the CT-ACEFed alloy. The purpose of this study is to provide a high-efficiency strategy to achieve Al–Mg alloys with superior mechanical performance and overcome the strength-ductility trade-off.