Lijun Han

This study systematically investigates the microstructural characteristics and mechanical properties of resistance spot-welded joints in 3 mm thick non-heat-treatable die-cast AlSi₇MnMg alloy, with particular focus on the influence of element segregation and secondary phase behavior on fracture mechanisms and the process window. The results indicate that the weld nugget exhibits a typical dual structure consisting of columnar and equiaxed grain zones, with a corresponding “M”-shaped microhardness profile. Significant segregation of Si, Fe, and Mn elements at the nugget boundary was observed, leading to the formation of low-melting-point eutectic regions and secondary phase bands. These features induce microporosity along segregation trajectories, serving as crack initiation sites and resulting in a notably narrowed spot welding process window. From the perspective of microstructure and solute behavior during non-equilibrium solidification, this work elucidates the intrinsic mechanisms governing joint performance and process stability in non-heat-treatable die-cast aluminum alloys, providing a theoretical basis for their engineering applications.

In this study, laser oscillation welding was utilized to offer an effective solution for the joint welding of heat-treatment-free die-cast aluminum alloys, which expands the practical applications of automotive structural parts and heat sinks for electronic devices. The effects of oscillation amplitude on the macro-morphology, microstructure, and properties of the alloy weld were examined, and a molten pool flow model was developed to compare the behavior of the molten pool with and without oscillation. The results show that increasing the oscillation amplitude eliminates the coarse Al₁₅(Fe,Mn)₃Si₂ phase, resulting in a finer and more uniform distribution of the eutectic Si and Mg₂Si phases. At an oscillation amplitude of 7 mm, the maximum tensile shear load and displacement were 2761 N and 1.17 mm, respectively. Laser oscillation was found to enhance the fluidity of the molten pool, reduce porosity, improve weld quality, and effectively decrease cracks and inhomogeneous grain distribution. These findings provide a research basis for optimizing the laser oscillation welding process and for the practical welding of fabricated devices.

To reduce the draught force of a traditional planar potato digging shovel (DZ), a biomimetic potato digging shovel (YS), inspired by the mole rat’s digits, is designed, using the biomimetic macroscopic surface modification method. The finite element simulations, soil bin experiments, and field experiments for DZ and YS are conducted to explore the factors affecting draught force and to verify the feasibility and effectiveness of the biomimetic potato digging shovel. Results show that the soil–shovel interaction models predict the draught force well, but the simulations for the soil rupture distance ratio need to be further improved. The studied factors all have a great influence on the draught force of DZ and YS and they follow the order of cutting speed > digging depth > mounting angle. For the single shovels, YS, compared with DZ, increases the draught force at a low mounting angle but decreases the draught force by over 8.41% when the mounting angle is higher than 30°; for the grouped shovels, the draught force and fuel consumption of YS, compared with those of DZ, decline by over 13.33% and 9.18%, respectively. The reasons for the reduction in the draught force of YS are to make the soil mass tend to move upward and to change the soil’s state of motion and stress continually; thus, the compaction to the soil is reduced, and the soil becomes easier to be broken.