Modification and strengthening of recycled Al-Mg-Si-based alloy upon continuous rheological extrusion (CRE) forming

Abstract

With global warming and resource scarcity, it is crucial to devise a simple, energy-efficient, and low-emission recycling method for aluminum alloys. In the recycled Al-Mg-Si-based alloy, the coarse α-Al dendrites, the long plate-like β-Al₅FeSi phase and bulk Mg₂Si phase significantly impair the microstructure and mechanical properties of the alloys. In this works, combined the continuous rheological extrusion (CRE) technology with the addition of CRE Al-5.0Ti-1.0B (wt%) refiner, the recycled Al-Mg-Si-based alloy wires at extrusion ratios (ER) of 3, 5 and 7 were prepared. The refinement of Mg₂Si and β-Al₅FeSi phases and the grain refinement caused by the continuous dynamic recrystallization (CDRX) behavior in the CRE process were discussed. The strengthening mechanism of recycled Al-Mg-Si-based alloy was revealed. The results showed that, CRE technology and CRE Al-5.0Ti-1.0B (wt%) refiner can effectively refine Mg₂Si and β-Al₅FeSi phases, and even to the nanometer level. At the same time, the increase of ER and the addition of CRE Al-5.0Ti-1.0B (wt%) can promote the transformation of low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs), thereby promoting the occurrence of CDRX. In addition, the increase of dislocations and nanophases caused by the increase of ER and the addition of CRE Al-5.0Ti-1.0B can effectively refine CDRX grains. When 0.2 wt% CRE Al-5.0Ti-1.0B (wt%) refiner was added at ER of 7, the ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of recycled Al-Mg-Si-based alloy were 259.40 MPa, 140.80 MPa and 18.20%, respectively. Grain boundary strengthening and dislocation strengthening were the primary mechanisms in enhancing the YS of the recycled Al-Mg-Si-based alloy.