Effect of integrated die-casting on microstructure and mechanical properties of large-scale complex thin-walled RE-Mg alloy components for new energy vehicles

In this work, vacuum-assisted high-pressure die casting (HPDC) was employed to fabricate an integrated RE-Mg alloy rear floor for new energy vehicles (NEVs). The correlations among microstructure evolution, mechanical properties, melt flow, and filling behavior of the integrated HPDC RE-Mg alloy rear floor were investigated. Each region of the casting was predominantly composed of fine globular grains. The shock absorber tower/wheel housing exhibited the finest grains, with an average diameter of 6.363 µm and a circularity of 0.81. The crossbeam exhibited relatively larger grains, with an average diameter of 9.945 µm and a circularity of 0.77. In the RE-Mg alloy rear floor, the network-like Al₃La phases were present at the grain boundaries, along with a small amount of randomly distributed block-shaped La(MnAl₂)₄ phases. During melt filling, the molten metal flowed predominantly in a smooth manner, with a local melt confluence phenomenon occurring in the crossbeam. The platform exhibited the optimal mechanical properties, with an ultimate tensile strength (UTS) of 234 MPa, a yield strength (YS) of 123 MPa, and an elongation of 11.8%. The crossbeam showed relatively lower values of 196 MPa, 117 MPa, and 7.6%. The dominant strengthening contribution came from grain refinement, followed by dislocation strengthening.