Strengthening mechanisms and high-temperature oxidation behavior of extruded hollow WE43 magnesium profile with lamellar heterostructures

A major challenge for the application of Mg alloy hollow profiles in railway vehicles is to simultaneously improve their mechanical properties and flame retardancy. This work fabricated a large-size asymmetric hollow profile of Mg-4.04Y-2.38Nd-1.02Gd-0.41Zr (WE43) alloy by porthole die extrusion. The influences of process parameters on the temperature and stress fields were investigated by finite element method (FEM). The microstructures were analyzed using a combination of optical microscope, scanning electron microscopy, transmission electron microscopy, spherical aberration transmission electron microscopy and X-ray electron diffraction. The mechanical properties of the alloy were evaluated using hardness and tensile testing methods. X-ray photoelectron spectroscopy was employed to conduct compositional analysis of the film following high-temperature oxidation. Lamellar heterostructures were formed in the extruded profile by high-temperature extrusion, with rapid cooling and a high extrusion ratio, followed by artificial aging. The average values of yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of the extruded profiles after T5 treatment were 291 MPa, 385 MPa, and 16.4%, respectively. The profiles demonstrate a good balance between strength and plasticity, attributed to the synergistic effect of weak basal texture, precipitation strengthening and heterogeneous deformation induced strengthening. Finally, the extruded hollow profile does not catch fire during high-temperature oxidation up to 1050 °C due to the protection of the dense Y₂O₃ and MgO composite layer on the matrix. This work is of great significance in guiding the application and industrial production of large-sized hollow profiles of WE43 alloy in railway vehicles.