Qin Yang

To support vehicle crash simulation in lightweight automotive design, this study develops high-precision constitutive and fracture models for a giga casting Mg-7Al-1.5La-1Zn magnesium alloy. Through mechanical testing and microstructural analysis, the plastic hardening, strain-rate strengthening, and ductile fracture behaviors are systematically investigated. A weighted mixed hardening model combining the saturation-type Hockett–Sherby and unsaturated Swift models is established. To overcome the limitations of the classical Johnson–Cook (J-C) model in capturing strain rate–plastic strain coupling, a modified dynamic increase factor incorporating equivalent plastic strain is proposed. Comparative fitting with the Cowper–Symonds model confirms that the modified J-C model better captures the twinning deformation mechanism under high strain rates and achieves higher accuracy. Among three fracture models Johnson–Cook (J-C), Modified Mohr-Coulomb(MMC), and Damage Initiation and Evolution Model (DIEM), the MMC model, which incorporates both stress triaxiality and Lode angle, shows the best predictive performance, with an average accuracy of 86.46% for fracture displacement across the full stress range. Microstructural characterization reveals grain refinement and dispersed Al₁₁La₃ precipitates that improve grain boundary properties. The established parameter set and calibration methods provide a reliable reference for material card calibration in crash simulation of giga casting magnesium alloy body structures.

Al-Si alloys are essential in manufacturing automotive body structural components due to their superior casting properties, high specific strength, and excellent corrosion resistance. The microstructural evolution and mechanical properties of Al-Si alloy used in rear floors were systematically investigated based on a casting simulation. The results indicate that the alloy microstructure consists of α-Al, an Al-Si eutectic, and the Al₁₅(Mn,Fe)₃Si₂ intermetallic phases. The accumulation of Al₁₅(Mn, Fe)₃Si₂ intermetallic compounds increases toward the end of the filling process, leading to a reduction in mechanical properties. The optimal filling distance of the alloy ranges from 210 mm to 450 mm, while the optimal thickness ranges from 3.36 mm to 4.14 mm. With a filling distance and thickness increase, the yield strength, tensile strength, and elongation of the alloy initially increase and then decrease. The optimal properties are achieved when the filling distance is 210 mm and the thickness is 4.14 mm, with a yield strength of 122.35 MPa, a tensile strength of 258.43 MPa, and an elongation of 11.60%. At the same filling distance, near the gate position, when the thickness increases from 4.1 mm to 5.3 mm, the alloy’s tensile strength and elongation decrease. However, at positions farther from the gate, when the thickness increases from 2.94 mm to 4.93 mm, both the tensile strength and elongation of the alloy increase. This study provides a theoretical basis for the process design of large integrated die-casting components for new energy vehicles and supports the development of a high-strength ductile Al-Si alloy material system.

Aluminum alloy die casting has achieved rapid development in recent years and has been widely used in all walks of life. However, due to its high pressure and high-speed technological characteristics, avoiding hole defects has become a problem of great significance in aluminum alloy die casting production. In this paper, the filling visualization dynamic characterization experiment was innovatively developed, which can directly study and analyze the influence of different injection rates on the formation and evolution of alloy flow patterns and gas-induced defects. As the injection speed increased from 1.0 m/s to 1.5 m/s, the average porosity increased from 7.49% to 9.57%, marking an increase in the number and size of the pores. According to the comparison with Anycasting, simulation results show that a liquid metal injection speed of 1.5 m/s when filling the flow front vs. the previous injection rate of 1.0 m/s caused fractures when filling at the same filling distance. Therefore, the degree of the broken splash at the flow front is more serious. Combined with the analysis of transport mechanics, the fracturing is due to the wall-attached jet effect of the liquid metal in the filling process. It is difficult for the liquid metal to adhere to the type wall in order to fuse with subsequent liquid metal to form cavity defects. With an increase in injection velocity, the microgroup volume formed via liquid breakage decreases; thus the volume of air entrapment increases, finally leading to an increase in cavity defects.

It is currently a challenge to accurately predict the deformation and fracture behavior of metal parts in automobile crashes. Many studies have shown that the deformation and fracture behavior of materials are significantly affected by the stress state during automobile crashes with complex stress state characteristics. In order to further promote the application of die-cast magnesium alloys in automobiles, it is particularly important to study the material deformation and fracture behavior of die-cast magnesium alloys. In this paper, the mechanical properties of the AM60B die-cast magnesium alloy sheet under four stress states (shear, tension, R10 notch tension, and cupping) were designed and tested. Based on the von Mises isotropic constitutive model and Swift weighted Hockett–Sherby hardening model, the plastic constitutive model of die-cast magnesium alloy was established. Based on the plastic model and the fracture model (JC, MMC, and DIEM) considering the influence of three stress states, the deformation and fracture behavior of the AM60B die-cast magnesium alloy front-end members in three-point bending were predicted by experiments and finite element simulation. The experimental results show that the deformation mode and loading–displacement curve trend of the AM60B die-cast magnesium alloy front members are the same, the crack initiation point and crack initiation time are the same, and the crack shape is similar. The results show that the complex stress state constitutive model parameters and the DIEM fracture model obtained in this paper can accurately predict the deformation and fracture failure behavior of the AM60B die-cast magnesium alloy sheet.