International Journal of Metalcasting最新文献

Strontium (Sr) is commonly used to modify the eutectic Si in hypoeutectic Al–Si alloys to improve mechanical properties. The present study is focused on the effect of electron configuration and electronegativity of alkaline earth metal Sr on the relatively more electronegative Group IV elements Si and Pb. The element Pb occurs as an impurity during the refining of secondary Al. The experiment was conducted on high-pressure die casting (HPDC) of commercial grade A380 aluminum alloy with Si level 7.5–9.5% modified with Al-9.7% Sr master alloy. Samples were cast by inserting a test bar cavity in the runner system of an experimental die. Thin foil electron microscopy (TEM) along with energy-dispersive spectroscopy and high angle annular dark field imaging was used to determine the atomic percent of Si, Sr, Fe, Cu, Mn, Pb, Sn, and Ti embedded in the Al–Si eutectic matrix. Results showed that Sr was primarily segregated in eutectic Si with trace amounts in solid solution in Al. Additionally, a trace amount of Sr was also detected in the impurity element Pb. This preferential distribution is attributed to the difference in electronegativity between Sr (Group II element) and the Si and Pb (Group IV element). Sr with two valence electrons (5s¹p¹) and an electronegativity of 1.0 preferentially segregates on eutectic Si, which has four valence electrons (3s²p²) and a relatively stronger electronegative force of 1. 8. Furthermore, a higher (e/a) valence electron-to-atom ratio of Si lowers the stacking fault energy which accelerates precipitation of Sr in the wider stacking faults and inhibits the growth of eutectic Si in an expected manner. Transmission electron microscopy (TEM) of the HPDC A380 alloy, in contrast, did not reveal any presence of Sr in intermetallic compounds formed by transition elements Fe and Cu. The TEM results indicate a strong correlation between the electron configuration and electronegativity of elements in the formation of stable intermetallic compounds.

High-Temperature Laser Scanning Confocal Microscopy (HT-LSCM) is an in situ technique that can be used for direct observation of the microstructure during melting, solidification, and solid-state cooling. Therefore, this tool is a powerful method that can be used to understand how cooling conditions affect the solidification structure and degree of alloy segregation in steel castings. In the current study, specimen shape and size were optimized for this technique using an ultra-low-carbon steel. HT-LSCM was then utilized to observe the melting and solidification phenomena as a function of cooling rate for the ultra-low-carbon steel as well as a high-alloy austenitic manganese and aluminum steel. The growth kinetics and evolution of the solid–liquid interface during solidification were derived from time-lapse videos. The resulting solidification microstructure was determined utilizing scanning electron microscopy.

The Mg–10Zn–5Al–0.2Sc (wt%) alloy was fabricated through gravity casting and subsequent heat treatment. The microstructure and precipitates of the alloy samples were meticulously examined using OM, SEM/EDS, and TEM/HRTEM. The results indicate that the microstructure of the alloy comprises a MgZnAl phase along with a minor presence of Al₂Sc. The incorporation of Sc serves to refine the grain size of the alloy while introducing vacancies and dislocations within the microstructure. After heat treatment, an abundance of rod-shaped nanoscale MgZnAl and MgZn phases precipitate within the grains, with these phases exhibiting a perpendicular relationship in terms of precipitation orientation, leading to the formation of numerous dislocations and planar defects. The nanoscale MgZnAl and MgZn phases, characterized by a hexagonally close-packed structure, contribute significantly (68.59%) to the enhancement of the yield strength of the heat-treated alloy. These phases demonstrate a degree of coherence with the α-Mg matrix, impeding dislocation motion, and effectively absorbing and storing dislocations, thereby mitigating strain and distortion concentrations within the phases during tensile deformation. This mechanism reinforces the strengthening effect of coherent interfaces, ultimately improving the strength and ductility of the alloy. After heat treatment, the alloy attains a tensile strength of 221 MPa, a yield strength of 208.45 MPa, and an elongation of 0.99%, representing enhancements of 33.13%, 38.88%, and 0.49%, respectively, compared to the matrix alloy.

During the investigation of the direct squeeze casting process for the production of Al-5Sn-Cu low-tin bearing alloy parts, particularly floating bushings, this study has explored the effect and mechanism of grain refiner on reducing macro-segregation within low-tin bearing alloys. This has provided an effective solution for Sn segregation in the alloy and broadened its application prospects in the bearing field. The findings revealed significant microstructural differences both in the longitudinal and transverse sections, and abnormal macro-segregation of Sn at hot spots without grain refiner. Conversely, grain refinement improved the microstructure, resulting in a uniform distribution of Sn, effectively mitigating the macro-segregation phenomena, especially at hot spot positions. The grain refiner promoted the growth of equiaxed crystals by generating numerous heterogeneous nucleation sites. These played a crucial role during the later stages of solidification by uniformly isolating the Sn-rich liquid phase and preventing the formation of feeding channels for this phase as solidification completed. These actions ultimately prevented the macro-segregation of Sn. The approach not only enhances the quality and reliability of these castings but also provides critical guidance for optimizing the manufacturing of aluminum-based bearing alloys.

The current approach to reclaiming inorganic binder waste sand discharged during the aluminum alloy casting process typically involves mechanical grinding combined with calcination treatment (650–700 °C). However, this method encounters challenges such as the accumulation of residual binder on the surface of the reclaimed sand and a subsequent decline in its refractoriness. This study proposes a novel method to reclaim inorganic binder waste sand, by integrating chemical infiltration with mechanical grinding. The effects of different types and concentrations of chemical reagents on the electrical conductivity and Na₂O content of the reclaimed sand were investigated. The microstructure and chemical composition of both waste and reclaimed sand were analyzed, and revealing the chemical-mechanical grinding reclamation mechanism. Compared to H₂C₂O₄ and MgCl₂ solution, the CaCl₂ solution demonstrates superior efficacy in enhancing the quality of reclaimed sand. The electrical conductivity and Na₂O content of the reclaimed sand exhibit a rapid decline followed by stabilization with increasing concentration of CaCl₂ solution. When the dosage of CaCl₂ solution is 5 wt% of the waste sand weight, and the concentration is 10 wt%, the electrical conductivity and Na₂O content of the obtained reclaimed sand are 776.7 μS/cm and 0.039%, respectively, meeting the utilization requirements for reclaimed sand. Microscopic analysis reveals that the CaCl₂ solution reacts with the residual binder on the surface of the waste sand, disrupting the structure and morphology of the residual binder. After drying, the reaction product crystallizes in the form of blocky inorganic salts, facilitating their removal during mechanical grinding. Finally, the clean reclaimed sand is attained, exhibiting a 24 h tensile strength exceeding 90% of that of new sand.

The gray cast iron is used in many machine parts such as pulleys, since it has excellent vibration damping, wear resistance, and castability. Material evaluation of this cast iron is important for quality assurance of machine products. This research proposes a method to identify defective products mixed with good products. Currently, test methods such as Brinell hardness and tensile strength tests are commonly used to check the quality of cast irons. However, these methods are not suitable for inspecting all products in terms of time required. Therefore, it is important to establish an electromagnetic nondestructive test that enables non-contact and fast measurement. It has been found that the use of AC magnetic fields in nondestructive testing methods can be used to measure defective gray cast iron. In this paper, we propose an electromagnetic nondestructive testing method that uses a DC-biased sinusoidal magnetic field, which enables measurements with higher sensitivity than those obtained with AC magnetic fields. The effectiveness of the proposed method is demonstrated through electromagnetic field finite element method (FEM) analysis using the play model method and corroborated by verification experiments.

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