This study examines the influence of key process parameters, specifically shot speeds and intensification pressure, on the microstructure and mechanical properties of non-heat-treated high-pressure die-cast AlSi9MnVZr alloy. Using a combination of 2D microstructural analysis and 3D reconstruction techniques, it is demonstrated that the absence of fast shot speed and intensification pressure results in a coarser microstructure characterized by larger externally solidified crystals (ESCs) and increased porosity, primarily in the form of large, irregular pores. Furthermore, the absence of these process parameters also lead to insufficient localize shear stresses, which prevents the disruption of the dendritic network and inhibits the formation of eutectic bands. In contrast, the optimal set of process parameters comprising slow shot speed, fast shot speed, and intensification pressure limit ESCs growth and promote a fine microstructure by reducing melt retention time in the shot sleeve through the shot speeds, while the intensification pressure improves feeding capability and interfacial heat transfer, resulting in a more uniform microstructure with small, predominantly spherical porosity. Additionally, intensification pressure alone plays a critical role in controlling both ESCs size and porosity; a lack of intensification pressure results in the formation of larger ESCs and more widespread shrinkage pores. Mechanical testing reveals that the alloy produced under optimal process conditions, comprising appropriate shot speeds and intensification pressure, exhibits the highest strength and elongation.
The silica sand particle size plays a crucial role in enhancing the sand-spreading effect and mechanical properties of sand mold via binder jetting 3D printing. Most prior work couples sand particle size with numerous process variables, making it difficult to isolate and elucidate the intrinsic mechanism of particle size alone. To overcome this limitation, a mathematical model describing inter-particle interactions based on the discrete element method was developed in this study. The particle flow code was employed to investigate how six silica sand particle sizes (0.12 mm, 0.14 mm, 0.16 mm, 0.18 mm, 0.20 mm, and 0.22 mm) affect the sand-spreading effect and mechanical properties of printed specimens, with the aim of quantitatively revealing the mesoscale governing relationships between silica sand size and particle packing, contact force transmission, as well as the specimen’s strengths. Concurrently, “8”-shaped and long-bar specimens were printed using the EXONE S-MAX system to measure their tensile strength and flexural strength. The experimental results demonstrate that as silica sand particle size increases, the porosity decreases initially and then increases, whereas the contact force magnitude, tensile strength, and flexural strength all exhibit an inverse trend of increase initially and then decrease. The optimal sand-spreading effect and mechanical properties are achieved at a silica sand particle size of 0.18 mm. Specifically, the simulated and experimental porosities are 4.24
Copper-tin alloys possess outstanding casting performance and wear resistance, and are mainly employed in the manufacturing of wear-resistant components under high load and high sliding velocity. To improve the strength of the CuSn10 cladding coating, the influence of Ni on the microstructure, microhardness, and tribological properties of the copper tin alloy was investigated. Four CuSn10 coatings with different Ni contents were fabricated on the 42CrMo steel by laser cladding technology. A corresponding numerical model was established by means of Ansys Workbench, and the optimum experimental parameters of the laser cladding process were derived. The simulation results indicate that when the laser power is 3,000 W, the scanning speed is 15 mm·s−1, and the powder feeding rate is 3.5 r·min−1, the CuSn10 coating with the best cladding effect can be obtained. X-ray flaw detection tests were conducted on the coatings, and the results indicate that the S3 coating (10wt.
In investment casting process, the temperature of the riser plays a critical role in solidification behavior and shrinkage feeding capacity. Riser temperature inevitably declines owing to multiple processes prior to pouring and heat exchange with the surrounding environment during casting. The centrifugal impeller, a key component of aerospace engines, was studied. A temperature field control method for the riser during casting was proposed, based on a quantitative analysis of pre-pouring temperature variations and their influence on shrinkage defects. By wrapping the riser with insulation cotton and applying riser insulation agent, the pre-pouring temperature loss of the riser is reduced by 76 °C and the solidification time is significantly extended. As a result, the number of shrinkage defects in the casting is reduced from 12 to 2, representing an 83.33
A pin-on-disk friction model was proposed based on the Archard theory, incorporating the arbitrary Lagrangian-Eulerian (ALE) remeshing technique and the Umeshmotion subroutine in Abaqus software. The model simulated the friction process between (TiC+TiB+La2O3)/TC4 composites and GCr15 steel, focusing on wear depth and stress-strain evolution. Meanwhile, the worn surface and cross-section of the composites were examined using advanced characterization techniques, and the friction behavior of the composite material was thoroughly investigated based on experimental observations and simulation results. The results indicate that the contact pressure during the wear process is non-uniformly distributed across the contact surface. The leading edge in the sliding direction experiences high normal stress and sliding shear stress under the combined action of the applied normal load and friction force. Consequently, this region exhibits the maximum equivalent stress and plastic deformation. With increasing friction temperature, the wear mechanism gradually transitions from severe abrasive wear to a combination of severe oxidative wear and slight adhesive wear. When the friction temperature reaches 500 °C, both the coefficient of friction and wear volume attain their minimum values, measuring 0.288 and 0.568 mm3, respectively. On one hand, the dense and flat tribo-layer generated on the worn surface contains a large amount of friction oxides, which acts as a solid lubricant, inhibiting the sliding shear stress generated during the friction process. On the other hand, the reinforced phases within the subsurface deformed zone disperse the stress concentration, thereby reducing crack initiation and hindering crack propagation in that region.
