Bimodal-Structured Al–Mg Alloy with High Strength and Ductility Processed by High Strain Rate Rolling at Medium Temperature

Abstract

A bimodal grain distribution is generated in the Al-6.5Mg alloy deformed by high strain rate rolling (HSRR) at 320 °C, in which the fine grains with the average size of 2.1 μm and the coarse grains with the size of hundreds of microns containing ultrafine sub-grains are developed. The deformed microstructures are detected by transmission electron microscopy, X-ray diffraction and electron backscattered diffraction. High strength and considerable ductility are achieved in the HSRRed alloy and the high strength is ascribed to solution strengthening, grain (sub-grain) strengthening and dislocation strengthening. The grain (sub-grain) strengthening is the dominant contributor (~ 146 ± 6 MPa) for yield strength. The generation of new fine grains is primarily observed along the deformation bands related to the high Mg solid content and the high strain rate at 320 °C. The dynamic recrystallization related to the deformation bands is proposed to build the bimodal grain distribution for achieving high strength and considerable ductility. A bimodal grain distribution is generated in the Al–Mg alloy during the high strain rate rolling (HSRR), the formation of fine grains (FGs) is related to the strain-induced deformation bands (DBs). The HSRRed alloy exhibits higher strength and larger ductility than the alloy experienced the traditional rolling (TR).