International Journal of Metalcasting最新文献

The primary objective of this investigation is to employ computational simulation analysis of casting to determine effective riser dimensions and eliminate shrinkage porosity in actual spheroidal graphite (SG) iron flywheel casting. A simulation software, Pro-CAST, is used to simulate the solidification process under varying process conditions (i.e., without a riser and with an effective dimension riser). The simulation results are then confirmed by a subsequent experiment using green sand casting. Additionally, a thorough investigation is conducted to determine the correlation between the shrinkage behavior and its morphological characteristics of the cast components. The simulation results infer that the un-optimized dimension of the riser causes the shrinkage porosity and void formation largely in the thicker section, due to the lower eutectic solidification time. However, when the dimension of the riser is optimized, this effect is mitigated simply by ensuring the eutectic solidification time is higher than the eutectic solidification of the thicker section; thus, the mold is completely filled with no shrinkage porosity or void formation. It is evident that there is a good agreement between simulation and experiment when comparing the resulting appearance of components in simulations and experiments.

Water-soluble salt core materials have high bending strength at room temperature. During high-pressure casting, water-soluble salt cores must withstand high temperatures and impact loads. To obtain a composite water-soluble salt core suitable for high-pressure casting components, sodium chloride and sodium carbonate are used as base salt materials. Ceramic particles of alumina are used as reinforcement materials in the preparation of a water-soluble composite salt core with excellent high-temperature strength via gravity casting. The microstructures of the salt core and fracture surface are observed and characterized. The use of alumina to enhance the sensitivity of the binary salt cores results in a low thermal crack sensitivity coefficient. The alumina particles dispersed in the matrix prevent crack propagation. Simulation results show that sodium aluminate has strong interfacial bonding abilities with other components in the salt core, affecting its high-temperature strength. Further results confirm that sodium aluminate formation enhances the high-temperature strength of salt cores.

Hypoeutectic Al-Si alloy (A360) is widely used to high-pressure die casting components used in the aerospace, automobile and building industries. An experimental investigation has been conducted concerning the effect of different rare earth Sc and Er additions on the solidification process of A360 alloy. The results indicate that a precipitation phase Al(Sc, Er)₂Si₂ is formed with the addition of Sc and Er elements. Moreover, the eutectic Si phase evolves from a coarse block-like and irregular polygonal into a granular morphology, and its average size value is decreased from 25.48 μm to 9.46 μm when the content of Sc–Er increases from 0 wt% to 0.6 wt%. In addition, the alloy exhibits an outstanding combination of mechanical and wear resistance properties at a Sc–Er addition of 0.6 wt%. Compared with the unmodified alloy, its ultimate tensile strength has increased from 82.7 MPa to 148.4 MPa and average friction coefficient has decreased from 0.689 to 0.504.

Graphical Abstract

Distortion can be a prominent issue in the production of metal casting components, especially when using metal dies. Existing research underscores the pivotal role of the temperature at which the solidified component is extracted from the mold in contribution to the ultimate distortion of the component. This numerical investigation seeks a comprehensive understanding of the factors governing deformation by employing simulations that emulate experimental conditions. The study utilizes coupled thermomechanical simulations, executed through the commercial software “Abaqus,” across varying demolding temperatures. The temporal evolution of distortion is examined, with a focus on influential factors such as elastic and thermal strain. A quantitative and qualitative comparison is drawn between simulation outcomes and experimental results. The difference between experimental and simulation results was observed to increase linearly with higher demolding temperatures. The potential for leveraging the qualitative similarity between experimental and simulation results as a foundation for the development of distortion control strategies is deliberated.

Thermal analysis is an effective approach for studying the characteristics of materials under different temperature situations. The study implemented cooling curve analysis (CCA), complemented by computational methods for precisely evaluating the temperature variation of the molten alloy by employing two thermocouples. An aluminium alloy with 1 wt.% Mg addition was melted in graphite crucible and subjected to various cooling conditions, which included normal, slow, fast, and fastest cooling rate conditions. Normal cooling condition (A) was achieved when the crucible was allowed to cool down to room temperature. Meanwhile, the slow cooling condition (B) was achieved when the crucible was allowed to cool within the Kaowool insulator chamber. In addition, the fast (C) and fastest (D) cooling conditions were attained when the forced airflow was directed at the crucible at minimum and maximum speed, respectively. The temperature data were collected via K-type thermocouples connected to a Ni 9129 data acquisition system and DasyLab software. Cooling curves, cooling curves with baselines, dendritic coherency points, and solid fractions were then recorded using OriginPro 2019b software. The liquidus, eutectic, and solidus temperatures were determined. The microstructure of the alloy sample was characterised by optical microscopy (OM), scanning electron microscopy (SEM), combined with energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analysis. The results show that the high cooling rates produced smaller and more globular grain structures. The highest cooling rate condition produced smaller and globular microstructure formation at 944 µm² and a circularity of 0.61, respectively. Meanwhile, the slow cooling condition produced the largest grain size at 1668 µm² and a circularity of 0.46. The results show that higher cooling rates result in a smaller and more spherical grain structure than other cooling conditions. This underlines the significant influence of the cooling rate on the development of the microstructure during the solidification process. This comprehensive thermal analysis study has shed light on the significant influence of Mg addition and different cooling conditions on the Al-Si alloy's thermal properties and microstructure formation. The results contribute to understanding alloy solidification and may have practical implications for materials engineering and manufacturing.

In this investigation, ZE41 magnesium alloys reinforced with 2% weight of SiC and B₄C were manufactured through stir casting route under an inert environment. The microstructure of the unreinforced alloy, exhibits α Mg grains with uniformly distributed β Mg₇Zn₃ intermetallic phases at the grain boundaries. The addition of ceramic reinforcements decreased the average grain size and also formulated thin β Mg₇Zn₃ phases compared to the denser ones observed in the pure base matrix. The results of this work demonstrated that the tensile strength of the composites improved due to particle strengthening, grain refinement and presence of dislocations at the intermetallic regions and the best results were obtained for the hybrid ZE41 matrix (ZE41 + 2% SiC + 2% B₄C). The tensile strengthening mechanisms of the composites are discussed and the expected theoretical values of yield strengths are calculated for comparison. Additionally, the specimens' elastic moduli were evaluated experimentally and theoretically (using the Tsai Halpin model), with the results showing good agreement, particularly for the hybrid composite. The morphologies of the fractured specimens were also analysed and it has been observed that the hybrid composite exhibited a ductile mode of fracture due to the presence of uniform dimples. The impact strength and hardness values of all the composites was also found experimentally and the best results were obtained for SiC and B₄C composites which played a vital role in the selection of reinforcement particles for developing the hybrid composites. The wear analysis of the composites and their surface morphologies displayed considerable increase in friction coefficient and specific wear rate for hybrid composites at low and high loads.

Graphical Abstract

The hot tearing susceptibility (HTS) of Mg–5Gd–6Y alloy with 1 wt% Zn and 0.5 wt% Zr additions is investigated based on the constrained rod casting experiments and thermodynamic calculation. It shows that a minor Zn addition aggravates the HTS which cannot even be compensated by the grain refining effect of a further Zr addition. Moreover, the alloys with minor Zn and Zr addition show earlier hot tearing initiation (before the volumetric contraction force reaching minimum value). According to the calculation of prevailing criteria, minor Zn and Zr additions affecting the HTS has little relationship with the changing of the Scheil solidification curves. The mass formation of the X-Mg₁₂YZn phases in alloys with a minor Zn addition is the main cause of earlier hot tearing initiation and higher HTS. The phases with a higher elastic modulus result in poor liquid feeding among the α-Mg matrix and early dendrite bridging, causing more cavities, earlier strain accumulation at hot spots, and consequently earlier hot tearing initiation and higher HTS.

The large solid waste discharge of investment casting shells is closely related to its unstable performance of shells and uncontrolled curing reaction. The unique advantage of microfluidic technology is that it can effectively control the chemical reaction process. In the present work, an environmentally friendly citric acid widely used in food as hardening agent was employed to cure a sodium silicate shells. Droplets of citric acid solution with a concentration of 1.5 × 10⁻³ mol/L were generated by microfluidic technology and spread on the surfaces of shell specimens driven by air flow to induce the shell hardening. The green-, fired-, residual-strength, high temperature self-weight deformation, and gas to permeability of the shell were investigated. The results showed that the peak strength reached 30.38 MPa for green shell and 10.61MPa for the fired shell, about 26.4% and 17.4% higher than the immersion method, respectively. The fracture morphology of the shell observed by SEM (Scanning Electron Microscopy) confirmed that the more uniform, and far less cracks and micropores formed on the sodium silicate film of shells hardened by microfluidic droplets than the dipping method. The analysis of FTIR (Fourier Transform Infrared Spectroscopy) reveals that the final products of sodium silicate gel cured by microfluidic droplets achieved a high degree of polymerization and generated a relatively dense Si–O–Si cellular structure. The phase composition and thermal stability of the shell were analyzed by XRD (X-ray Diffraction) and TG-DSC (Thermogravimetric Differential Scanning Calorimetry). The results demonstrate that the improvement in hardening performance of shells is due to reaction microfluidic technology that can precisely control the volume and rate of hardening agent droplets, which can improve the repeatability and stability of the reaction in a short time, as well as reduce the damage of the gel film during the hardening process, and improve the quality of the gel film. The resulting shell can achieve higher strength and stability.

It has been a challenging mission to assure that ductile iron castings meet customer internal soundness specifications with acceptable process capabilities to get approval in new automotive model launch processes. Shrinkage conditions were investigated in the new program launch stage. Several factors were investigated including carbon equivalent, carbon levels, silicon levels, molten iron preconditioners and other additives. This study investigated shrinkage size by taking digital photos and measuring each shrinkage indication size using software comparing to the size limits from the customer Internal Soundness Specification. Thermal analysis was utilized to evaluate iron conditions to correlate shrinkage tendency. Statistical tools were applied to determine whether the factors in this investigation truly affected casting shrinkage characteristics. High process capability (Ppk) values were achieved by adopting optimal process parameters and using proper additives, and the program was launched successfully. Additional studies were conducted to confirm that the ductile iron meets customer specification including mechanical properties, microstructure, impact property, and casting hardnessunder all conditions.