The casting magnesium alloy AZ91D cannot be extruded at room temperature. This paper presents a process for extruding internal threads using AZ91D heated by electromagnetic induction. The feasibility of the process is verified by finite element simulation and experiments. Using DEFORM-3D to simulate the process of extruding a M12 × 1.25 mm threaded hole by electromagnetic induction-assisted heating, the equivalent stress-strain and material flow law in the process of thread deformation was analyzed and verified by experiments. Three parameters—hole diameter, machine speed and heating temperature—were considered to study the influence of different process conditions on the forming torque. The results show that a heating temperature above 523 K can improve the plasticity of AZ91D. The hole diameter has an important influence on the forming torque. The forming process is not suitable for high-speed machining. The surface metal of the thread formed by this process has a strong deformation layer, which can improve the strength and hardness of the thread.

Strengthening Mg alloys with rare earth elements has been a research focus for several decades. To minimize the usage of rare earth elements while enhancing mechanical properties, we adopted the strategy of alloying with multiple rare earth elements, namely Gd, Y, Nd, and Sm. Additionally, to promote the precipitation of basal precipitate, Ag and Zn doping was also induced. Thus, we designed a new cast Mg-2Gd-2Y-2Nd-2Sm-1Ag-1Zn-0.5Zr (wt.%) alloy. The microstructure of the alloy and its relevance to mechanical properties in various heat treatment conditions were investigated. After undergoing a heat treatment process, the alloy demonstrated exceptional mechanical properties, with a yield strength of 228 MPa and an ultimate tensile strength of 330 MPa achieved through peak-aging for 72 h at 200 °C. The excellent tensile properties are due to the synergistic effect of basal γ″ precipitate and prismatic β′ precipitate. In its as-cast state, its primary mode of fracture is inter-granular, whereas in the solid-solution and peak-aging conditions, the predominant mode of fracture is a mixture of trans-granular and inter-granular fractures.

Strengthening the CoCrFeNi high entropy alloy with a face-center cubic structure has become a research prospect in the last decade. Alloying with double elements, Nb and Mo, is an effective method. In this paper, to further enhance the strength of the Nb and Mo contained high entropy alloy, CoCrFeNiNb_0.2Mo_0.2 was annealing treated at different temperatures for 24 h. As a result, a new kind of Cr₂Nb type nano-scale precipitate with a hexagonal close-packed structure was formed, which is semi-coherent with the matrix. Moreover, by adjusting the annealing temperature, the precipitate was tailored with a considerable quantity and fine size. The best overall mechanical properties were achieved in the alloy annealed at 700 °C. The yield strength, ultimate tensile strength, and elongation are 727 MPa, 1.05 GPa, and 8.38%, respectively. The fracture mode of the annealed alloy is a mixture of cleavage and necking-featured ductile fracture. The approach employed in this study offers a theoretical foundation for enhancing the mechanical properties of face-centered cubic high entropy alloys via annealing treatment.

In order to explore the microstructure evolution of an Mg-RE alloy refined by Al during solution treatment, an Mg-3Y-4Nd-2Al alloy was treated at 545 °C for different time periods. Phase evolution of the alloy was investigated. After solution treatment, the Mg-RE eutectic phase in the Mg-3Y-4Nd-2Al alloy dissolves, the granular Al₂RE phase does not change, the acicular Al₁₁RE₃ phase breaks into the short rod-like Al₂RE phase, and the lamellar Al₂RE phase precipitates in the grains. With the extension of solution time, the precipitated phase of the lamellar Al₂RE increased at first and then decreased, and its orientation relationship with the matrix is ${<112>}_{{\mathrm{Al}}_2\mathrm{RE}}{//<2\overline{1}\overline{1}0>}_{\mathrm{Mg}}$ and ${\left\{111\right\}}_{{\mathrm{Al}}_2\mathrm{RE}}{//\left\{0002\right\}}_{\mathrm{Mg}}$. The undissolved granular Al₂RE phase can improve the thermal stability of the alloy grain by pinning the grain boundary, and the grain size did not change after solution treatment. Solution treatment significantly improved the plasticity of the alloy. After 48 h of solution treatment, the elongation increased to 17.5% from 8.5% in the as-cast state.

To reduce ram deflection and positional deviation at the boring spindle front end of a floor-type milling and boring machine under large extension, a ram-boring spindle assembly was investigated. A finite element model was established based on the actual structure, guideway support, and spindle assembly. Gravity-induced deformation and vertical displacement at the boring spindle front end under different extension conditions were analyzed to identify weak regions. The Solid Isotropic Material with Penalization method was then used to optimize the adjustable internal region of the ram with the objective of reducing structural compliance. The topology–density distribution and the deformation characteristics under different extension conditions were then used to guide an engineering reconstruction of the internal stiffeners, considering casting, assembly, internal space constraints, and engineering experience. Static analysis, displacement testing, and modal analysis were performed to verify the optimized structure. Results show that the maximum total deformation under simultaneous maximum extension decreased from 0.10268 mm to 0.097325 mm, while the mass decreased from 2424 kg to 2363 kg. The measured vertical displacement decreased from 0.114 mm to 0.108 mm. The first six natural frequencies increased by 1.48–5.91%. The proposed reconstruction improves deformation control and dynamic performance while reducing mass.

We developed a multiscale numerical model that couples a macroscopic temperature field with a cellular automaton (CA) model to investigate the evolution of the solidification microstructure in the molten pool of Q450NQR1 weathering steel during low-frequency vibration-assisted gas metal arc welding (GMAW). First, finite element analysis was used to obtain the transient temperature field of the molten pool, and temperature data from a representative cross-section were transferred to the CA computational domain. We then incorporated a vibration model and a dendrite fragmentation mechanism into the CA framework to simulate dendrite nucleation, growth, and microstructural evolution under different vibration frequencies and amplitudes. Welding experiments were also conducted to assess the model’s ability to reproduce the response trends associated with changes in vibration parameters. Without vibration, pronounced solute segregation occurred in the molten pool, and the weld microstructure was dominated by columnar grains and coarse equiaxed grains. After vibration was applied, low-frequency mechanical vibration enhanced dendrite fragmentation and promoted the conversion of fragmented dendrites into stable nuclei, thereby facilitating equiaxed grain formation and grain refinement. At a vibration amplitude of 0.10 mm, increasing the vibration frequency from 0 to 50 Hz reduced the average grain size from 68.5 μm to 35.2 μm, corresponding to a grain refinement rate of 48.6%. At 50 Hz, increasing the vibration amplitude further reduced the grain size and improved solute redistribution. These results indicate that, within the parameter range investigated in this study, low-frequency mechanical vibration refines the weld microstructure by promoting dendrite fragmentation and equiaxed grain formation. It also enhances effective solute diffusion during solidification. The simulated microstructural evolution trends agreed well with the experimental observations. These findings provide a basis for optimizing vibration parameters in vibration-assisted GMAW and for controlling the solidification microstructure of welded joints.