A systematic study of channel-angle effects on microstructure, strength-ductility, and corrosion behavior of high-purity magnesium in forward-parallel extrusion

This work systematically investigated the processing of high-purity magnesium by forward extrusion (FE) and forward-parallel extrusion (FPE) with three different channel angles of 90°, 105° and 120°. Tensile testing, electrochemical measurements, hydrogen evolution, weight loss tests and microstructural characterization were employed to clarify how the additional FPE shear path tailored the microstructure, mechanical properties and corrosion behavior relative to conventional FE. Compared with Φ10FE, FPE produced finer and more homogeneous grain structures, increased the fraction of high-angle grain boundaries and further weakened the basal texture. The yield strength increased from 33 MPa after Φ10FE to approximately 71 MPa after all FPE routes. The ultimate tensile strength was also markedly enhanced, increasing from 119 MPa for Φ10FE to 191 MPa, 182 MPa and 197 MPa for 90°FPE, 105°FPE and 120°FPE, respectively. Meanwhile, the elongation improved from 7.5% for Φ10FE to 10.1% and 9.8% for the 90°FPE and 105°FPE samples, respectively, while the 120°FPE sample retained a high elongation of 9.0% together with the highest tensile strength. Long-term immersion tests further showed that FPE reduced hydrogen evolution compared with Φ10FE, with the 90°FPE sample showing the lowest hydrogen release and corrosion rate. The corrosion-rate order was 90°FPE <105°FPE <120°FPE < Φ10FE < cast. These results demonstrate that FPE provides additional microstructural and property advantages over conventional FE, and that channel-angle selection enables high-purity Mg to be tuned toward either higher strength or improved ductility/corrosion resistance.