大型砂型差压铸造 EV31A 合金铸件组织及力学性能

The microstructures and mechanical properties at room and elevated temperatures of a sand differential pressure casting EV31A parts were evaluated. The as-cast microstructure of alloy is composed of primary-α-Mg with fine grain size of 65.02 μm and eutectic Mg₄₁ （Nd_0.6Zn_0.29Gd_0.11）₅ phase. After solution treatment，Mg₄₁ （Nd_0.6Zn_0.29Gd_0.11）₅ phase is dissolved into the matrix with few granular Mg-RE residues at grain boundaries with an increased mean grain size of 74.33 μm. The peak aged microstructure consists of β′+β₁，showing a satisfied tensile strength of 312.3 MPa，yield strength of 174.2 MPa and elongation of 6.9% at room temperature，respectively. The tensile strengths is decreased gradually below 200 ℃ with an obvious drop at 250 ℃ . The yield strength is declined linearly in range of room temperature to 250 ℃，while the elongation is increased linearly. The fracture mode is characterized by cleavage at room temperature. In the temperature range of 100~200 ℃ ，the fracture mode presents quasi-cleavage fracture，which is converted to mixed fracture at 250 ℃.