Refining grain structure and improving elongation properties in AZ31 magnesium alloy sheets using hard plate accumulative roll bonding

Abstract

Magnesium alloy sheet are an ideal choice for achieving material and structural light weighting. Traditional ARB technology can significantly reduce the size of magnesium alloy sheet, but it is faced with the challenge of strong plastic inversion. In addition, it is easy to produce edge cracking defects, and it is also difficult to control the quality of the sheet. In this study, we prepared AZ31 magnesium alloy sheet by HP-ARB process for the first time. The results show that compared to ARB, the HP-ARB sheet has remarkable improvements in and mechanical properties.After two passes, the average grain size of HP-ARB decreased from 6.19 μm to 4.58 μm, tensile strength reaches 291 MPa, and the elongation is 10.1%, which significantly increased to 55.4% compared with ARB. HP-ARB has the ability to transform part of shear stress into compressive stress, which improves the stress distribution on the sheet. On one hand, a large amount of energy stored in dislocations provides energy for DRX, which makes the process more complete, leading to microstructure refinement and grain orientation randomization. This leads to the deviation of texture orientation to TD direction, which leads to the decrease of pole density and weakening of the strong basal texture. On the other hand, dislocation density (ρD) of the sheet is relatively low. The average Schmidt factor of prismatic <a> slip and pyramidal <c+a> slip in the HP-ARB process is higher, which is beneficial to dislocation slip, thus promoting an increase of sheet elongation. This provides a new strategy for the forming and manufacture of high performance magnesium alloy sheet.