Study of the microstructure, bonding evolution and mechanical properties of continuously extruded magnesium AZ31 sheet

Magnesium (Mg) alloys have considerable potential for lightweight applications in many industrial sectors. However, developing a cost-effective sheet forming process is extremely challenging because its poor formability leads to severe edge cracking, which limits their extensive applications. To overcome this challenge, scholars proposed a continuous extrusion extending forming (CEEF) method to produce Mg alloy sheets through solid-state extrusion welding of two rods. An AZ31 Mg sheet (160 mm width and 8 mm thickness) was produced through CEEF. The microstructure, texture and properties of the formed AZ31 Mg alloy sheet were investigated using experimental and finite element simulation. The high deformation strain (≥200%) and the high temperature in the welding region led to good welding quality. Banded microstructures and numerous tensile twins were found in the welding region and might result from <c+a> non-basal slip and rotational dynamic recrystallisation. The (0001) basal poles were inclined approximately 45° with respect to extrusion direction (ED) at the entrance of the chamber. No cracks occurred in the welding regions of the transverse direction (TD) samples. The tensile strength of the welding region was comparable with that of the feedstock area. The largest elongation of 18.6% versus 20% of the feedstock materials was observed in the samples along the extrusion direction. The high tensile strength of the welding region was attributed to the large number of tensile twins.