Yongkun Li

7xxx series aluminum alloys exhibit high strength and low density; however, their high degree of alloying results in a pronounced hot-cracking tendency, making direct casting forming challenging. In this study, a rheo-squeeze-cast AA7075 alloy was investigated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and room-temperature tensile testing were employed to systematically examine the effects of the solution treatment window on the microstructure and mechanical properties of the castings. The distinctive contribution of this work is the quantitative correlation of solution-time-dependent second-phase evolution and porosity with the tensile behavior of ECSC-assisted rheo-squeeze-cast AA7075. The results show that, with increasing solution treatment time, the intergranular eutectic phases gradually dissolved, and their morphology evolved from lamellar structures into fine rod-like features. When the solution treatment time was extended to 12 h, a small number of pore defects appeared in the microstructure. Under the conditions of solution treatment at 470 °C for 8 h followed by aging at 120 °C for 24 h, uniformly distributed Zn–Mg-rich aging precipitates were observed in the matrix, resulting in the best comprehensive mechanical properties, with an ultimate tensile strength, yield strength, and elongation of 498.1 MPa, 413.7 MPa, and 8.2%, respectively. The optimized heat-treatment condition provides a practical route for achieving a favorable strength–ductility balance in rheo-squeeze-cast AA7075 components.

To simultaneously suppress shrinkage-related defects and refine the solidification microstructure of Mn70Ni25Cr5 alloy ingots, ProCAST simulation was combined with Box–Behnken response surface methodology to optimize pouring temperature, filling time, and mold temperature. Porosity in the ingot body and secondary dendrite arm spacing (SDAS) were selected as the response variables, and quadratic regression models were established for both responses. The optimized casting parameters were determined using analysis of variance, response surface analysis, and the desirability function approach. The porosity and SDAS models were both statistically significant, with non-significant lack-of-fit terms and R² values of 0.9906 and 0.9901, respectively. The optimal parameters were a pouring temperature of 1220.74 °C, a filling time of 6.34 s, and a mold temperature of 294.47 °C, corresponding to a predicted porosity of 0.426% and a predicted SDAS of 47.51 μm. A supplementary simulation and a validation casting experiment were then performed using practical process settings derived from the optimized solution. The supplementary simulation indicated that shrinkage-related defects were concentrated mainly in the riser, while metallographic examination revealed no large continuous shrinkage-porosity region in the examined ingot-body sections. The overall measured SDAS across the center, half-radius, and edge positions was 48.54 μm, differing from the response-surface prediction by approximately 2.2%. These results support the applicability of the combined ProCAST–RSM approach for simulation-assisted optimization of Mn70Ni25Cr5 alloy casting parameters within the investigated process range.

To reveal the stress–strain response and microstructure evolution of 38MnVS6 non-quenching and non-tempering steel pistons during hot forging, this study combines finite element simulation with experimental validation to investigate the effects of deformation temperature and strain rate on equivalent stress, true stress–true strain curves, and grain evolution. The results show that the deformation resistance of 38MnVS6 steel decreases with increasing temperature and increases with higher strain rates. Under 1000–1050 °C and a strain rate of approximately 1 s⁻¹, the stress distribution in the forging is relatively uniform, and stress concentration is effectively relieved. An Arrhenius-type high-temperature constitutive equation is established based on peak stress data, yielding a deformation activation energy Q of 335.99 kJ·mol⁻¹, which accurately represents the flow stress variation under different hot deformation conditions. Grain evolution simulated using the CAFE model indicates that 50% deformation promotes dynamic recrystallization and refines the grains. Experimental results show that water cooling increases the tensile strength by approximately 35% compared with air cooling, although the plasticity slightly decreases. In contrast to existing studies on general operating conditions, this paper establishes a coupled correlation mechanism linking the thermal deformation parameters–cooling regime–microstructure–mechanical properties. The findings provide important theoretical foundations and engineering references for the optimization of precision forging processes for non-quenched and tempered steels, the precise control of the microstructure and properties, and the quality control of forgings.

Conventional casting of 5N5 high-purity aluminum often results in coarse grains, microstructural inhomogeneity, and a low equiaxed grain area fraction. Vacuum casting in a graphite mold was integrated with multidirectional mechanical vibration to refine and homogenize the solidification microstructure. A three-factor, three-level Box–Behnken design combined with response surface methodology was employed to optimize pouring temperature (A), mold temperature (B), and vibration frequency (C), with the average grain size (Y₁) minimized and the average shape factor (Y₂) and equiaxed grain area fraction (Y₃) maximized. Analysis of variance indicated statistically significant quadratic models with a non-significant lack of fit. The predicted optimum (A ≈ 714 °C, B ≈ 363 °C, C ≈ 37 Hz) was validated experimentally, producing a refined and highly equiaxed structure (Y₁ ≈ 0.85 ± 0.02 mm, Y₂ ≈ 0.84 ± 0.04, Y₃ ≈ 88.6 ± 2.11%), consistent with model predictions. Multidirectional vibration strengthens melt convection and interfacial shear, which is considered to promote grain multiplication and increase the number of effective nuclei, thereby accelerating the columnar-to-equiaxed transition and improving microstructural uniformity.

Conventional casting of 5N5 high-purity aluminum often results in coarse grains, microstructural inhomogeneity, and a low equiaxed-grain area fraction. Vacuum casting in a graphite mold was integrated with multidirectional mechanical vibration to refine and homogenize the solidification microstructure. A three-factor, three-level Box–Behnken design combined with response surface methodology was employed to optimize pouring temperature (A), mold temperature (B), and vibration frequency (C), with the average grain size (Y1) minimized and the average shape factor (Y2) and equiaxed-grain area fraction (Y3) maximized. Analysis of variance indicated statistically significant quadratic models with non-significant lack of fit. The predicted optimum (A ≈ 714 °C, B ≈ 363 °C, C ≈ 37 Hz) was validated experimentally, producing a refined and highly equiaxed structure (Y1 ≈ 0.85 mm, Y2 ≈ 0.84, Y3 ≈ 88.6%), consistent with model predictions. Multidirectional vibration strengthens melt convection and shear, promoting dendrite fragmentation and increasing effective nucleation, thereby accelerating the columnar-to-equiaxed transition and improving microstructural uniformity.

In this paper, the ultrasonic vibration treatment (UVT) technique was used to prepare a SnSbCu11-6 alloy semi-solid slurry, and the effects of ultrasonic power on its microstructure size, distribution and properties were studied. The results show that the UVT technique significantly refines the Cu6Sn5 phase and SnSb phase and improves their distribution uniformity. Interestingly, the second SnSb phase is also well refined to nearly 100 °C below the melting point; furthermore, the morphology is transformed from coarse petal-like to fine regular cubic, and the average grain size is refined to 48.8 ± 8.8 μm. The alloy’s comprehensive properties are best when the ultrasonic power is 1200 W. The yield strength, tensile strength, elongation and microhardness reach 60.6 MPa, 70.3 MPa, 4.9% and 27.4 HV, respectively, which represent increases of 4.7%, 6.0%, 113% and 23.4%, respectively, compared with conventional liquid casting. This may be attributed to the grain size refinement and distribution uniformity enhancement of the Cu6Sn5 phase and the SnSb phase. This work provides a feasible and effective method for the preparation of high-performance tin-based babbitt alloys by UVT technology.