International Journal of Metalcasting最新文献

The present investigation aims to fabricate functionally graded aluminium alloy A356 processed through stir casting followed by vertical centrifugal casting. The hardness was examined using a Vickers’s microhardness tester, and the microstructure was examined through an optical microscope (OM), high-resolution scanning electron microscope (HRSEM), and X-ray diffraction (XRD) instrument. The dry sliding wear behaviour was examined using a pin-on-disc tribometer to study the influence of ageing temperatures (145, 165, and 185 °C), various zones (outer, middle, and inner) and applied load (10, 20, and 30N) on the specific wear rate (SWR) and coefficient of friction (COF). The sample aged at 165 °C had a 50% higher maximum hardness in the higher hardness zone than the as-cast FG aluminium alloy. Taguchi's technique and analysis of variance (ANOVA) determined the best and most significant sliding wear variables. The lowest SWR and COF of 0.00100 mm³/Nm and 0.382 were identified at the 165 °C aged higher hardness zone with a load of 10 N, and ANOVA analysis revealed that the applied load had a major impact. The worn surface examination confirmed the minimal wear damages in the higher hardness zone with an abrasive wear mechanism. The wear debris examination confirmed the oxide layer formation due to the tribochemical reactions.

When an aluminum investment casting with a complex internal cavity or deep pore is fabricated, a core that can be dissolved and collapsed in water is needed. In this paper, a water-soluble ceramic core with fused corundum powder as refractory material and K₂SO₄ as binder was prepared. The results show that as the content of K₂SO₄ increases, the bending strength, porosity, and shrinkage of the core decreases, but the solubility of the core improves. The K₂SO₄ will decompose and react with Al₂O₃, resulting in the low-soluble KAlO₂ produced. The solubility of ceramic cores is affected by the porosity, the reacting product, and the residual salt. When the amount of binder is 30 wt.%, the core possesses the best comprehensive properties. In three conditions: hot water at 80 °C, ultrasonic vibration, and mechanical stirring assistance processes, the core has the fastest dissolution rate with ultrasonic assistance. An S-shaped core embedded in aluminum casting was fabricated, and the core was removed completely in water with ultrasonic assistance. The pore surface of the casting was bright and clean, which means that the water-soluble ceramic core prepared in this paper was expected to be used to produce the aluminum alloy casting with complex inner cavities.

Permanent mold (PM) and semi-solid (rheo) casting in ductile iron castings (DIC) were studied, and the microstructure was aimed to be chill free in as-cast condition. Denitrification was conducted understanding solubility properties of nitrogen in base molten iron, and re-nitrification was strictly avoided during molten treatment by Mg alloy. As the results, chill-free knuckle castings were possible with both casting methods in as-cast condition. The knuckle castings had no shrinkage cavity also. The solidification time by rheocasting was shorter than that of PM casting. It was approximately one in two and a half. The castings had ultrafine spheroidal graphite which were mostly under 10 µm. The graphite structure by rheocasing method was finer and more uniform than those of PM casting. The tensile strength in castings with both casting methods was approximately 1.3 times keeping elongation over 10% comparing with conventional sand knuckle castings. It was concluded that free nitrogen (N_F) promoted chill formation, and chill could be avoided by promoting denitrification and minimum re-nitrification.

The effects of Er addition and solution treatment on the microstructure characteristics, tensile properties, and fracture behavior of a hypoeutectic Al–10%Mg₂Si–3.5%Cu alloy were systematically studied. The results showed that the addition of 0.45 wt% Er to hypoeutectic Al–10Mg₂Si alloy without and with the addition of 3.5 wt% Cu can significantly reduce the grain sizes of the eutectic Mg₂Si phase and α-Al/Mg₂Si eutectic cell, and transform the morphology of the eutectic Mg₂Si from coarse Chinese characters to thin stripes, dots, and fibers. The modification of eutectic Mg₂Si is attributed to the inhibition of Er on the heterogeneous nucleation of AlP by forming Er, P-containing phases, and the enrichment of Er atoms around eutectic Mg₂Si, which inhibits the growth of eutectic Mg₂Si and promotes a change in its growth direction. The solid solution treatment causes the eutectic Mg₂Si to tend towards spheroidization, which is promoted by the addition of Er. The addition of 0.45 wt% Er simultaneously improves the strength and plasticity of the cast alloys without and with the addition of 3.5 wt% Cu. The solid solution treatment further improved the tensile properties of the studied alloys. The improvement in strength of the alloy after as-cast and T6 treatment is due to the obstruction of fine eutectic Mg₂Si and containing-Er/Cu intermetallic compound particles on dislocations, while the improvement of plasticity mainly lies in the reduction of stress concentration and stress uniformity around eutectic Mg₂Si and intermetallic compounds caused by the regularity and spheroidization of their morphology.

This study investigated the artificial aging process of TiB₂/Al–5Cu composite, with a focus on the influence of TiB₂ particles on the precipitation behavior of the composite. Additionally, a comparative analysis of the microhardness and tensile properties between the TiB₂/Al–5Cu composite and the Al–5Cu alloy was conducted. X-ray Diffraction (XRD) analysis reveals that the TiB₂/Al–5Cu composite consists of TiB₂ and Al₂Cu phases. The Scanning Electron Microscopy (SEM) imagery demonstrates a predominantly cellular crystal composition in the composite. Notably, as the aging time progresses, there’s an initial increase followed by a subsequent decrease in the gray grain boundaries of the composite. Transmission Electron Microscopy (TEM) images uncover the presence of needle-like θ phase, TiB₂, and dislocations within the TiB₂/Al–5Cu composite. The incorporation of TiB₂ particles has emerged as a pivotal factor in significantly curtailing the artificial aging duration. With the peak hardness aging time determined at a mere 8 h, the TiB₂/Al–5Cu composite showcases substantially higher hardness levels compared to the Al–5Cu base alloy. Remarkably, the optimum aging time for achieving the best mechanical properties in the composites is reduced from 20 to 8 h. Directly comparing the TiB₂/Al–5Cu composite to the Al–5Cu alloy under peak aging conditions, notable enhancements in both yield strength (22%) and tensile strength (41%) are observed. Additionally, a slight increase in elongation is observed in the TiB₂/Al–5Cu composite.

It is of great significance to effectively prevent the stray grain defect at the edge plate of nickel-based superalloy single crystal blades. In this study, the evolution of the mushy zone and the growth of grain adjacent to the edge plate was first simulated by the temperature field and cellular automaton-finite element (CAFÉ) model, combined with a single crystal blade solidification experiment; it was proved that modifying the withdrawal rate alone was insufficient to prevent the stray grain formation. Then, the formation reason of the heat barrier zone and the irregular distribution pattern of the mold shell thickness were revealed by quantifying the present mold shell thickness near the edge plate through an industrial conical beam computed tomography. Based on these results, a combined control method for stray grain was proposed, which involves the use of precise measures such as non-uniform mold design, exact addition of process bars, and variable withdrawal rate. Simulation analysis demonstrated that this method can substantially reduce the undercooling range and average undercooling at the edge plate by 45.5% and 31.6%, respectively, and then eliminate the isolated undercooling zone. The macrostructure and microstructure of the blade cast by this method verified the effectiveness in inhibiting stray grain, and it will be a promising approach to manufacturing single crystal blades.

In this study, a micromechanical approach is used to investigate the deformation behaviour of rheocast Al–7Si–0.3Mg alloy. The alloy is rheocast using a cooling slope (at 45° and 60° angles) after melt treatment with a grain refiner addition (0.15% by weight Al–5Ti–1B master alloy). The comparison is made with the conventionally cast sample of the same alloy. Microscale instability of the rheocast alloy occurring at the onset of deformation, due to the strain incompatibility between the primary and eutectic phases, causes stress and strain localization as well as a triaxial state of stress, which subsequently governs void initiation and growth in the said alloy. A commercial finite element (FE) code ABAQUS is used to simulate microscale deformation behaviour of the three-dimensional representative volume elements (RVE) of approximated and as well as actual microstructure of the said alloy under uniaxial tensile loading. Although, globally uniaxial tensile loading is applied over the RVEs, however, stress triaxiality causes local variation of stress state, as evident from biaxial tensile stress state observed at grain boundaries of the above-mentioned RVEs, whereas uniaxial tensile stress is observed at the central location of these RVEs. Simulation results reveal that the macroscale deformation behaviour of the said alloy is determined by its microscopic features such as shape, size, distribution (spread of primary Al grains within the volume element) and volume fraction of primary Al grains. Moreover, distribution as well as volume fraction of eutectic Si also plays deciding role in deformation behaviour of the alloy. The FE model predictions of improved deformation behaviour/stress distribution evidenced in the rheocast + grain refined alloy is validated via phase level mechanical properties of the alloy, estimated from nanoindentation.

The present paper is on the processing of Al (A356)- reduced Graphene Oxide (rGO) composites by the squeeze casting technique to obtain improved mechanical and thermal properties. Reduced graphene oxide, a two-dimensional carbon allotrope with very high mechanical properties and thermal conductivity is used as a reinforcement in A356 aluminum alloy. Graphite was initially converted to rGO using the Hummers Method. 0.3 to 0.75 wt% weight percentages of rGO were incorporated into the aluminum alloy using a combination of stir mixing in semisolid state followed by squeeze casting, a hybrid method was employed to produce rGO reinforced A356 alloy matrix composite after applying mechanical stirring for uniform dispersion. Squeeze pressure was crucial for increasing the cooling rate to get finer microstructure, and eliminating the porosity. Reduced Graphene oxide uniformly within the Al 356 alloy matrix by applying both mechanical stirring for dispersion and squeeze pressure for rapid solidification and pore free casting. The squeeze cast Al 356-0.5%rGO composites after T6 heat treatment had an increase in tensile strength from 260 MPa for A356 alloy to 346 MPa, an increase in hardness 106 BHN to 130 BHN, and a reduction in coefficient of thermal expansion (CTE) from 21.7 × 10⁻⁶/°C to 10.8 × 10⁻⁶/°C at RT-50 °C. These results suggest potential applications of these composites in high performance industrial, automotive, and aerospace sectors.

A bottom-filled rigging system was designed to produce gray iron castings, which was compared with a top-filled design in the present study. Filling and solidification of gray iron produced with the bottom-filled mold were compared with that for the top-filled mold. At similar cooling rate and solidification condition, the count of Type A graphite flakes was greater in the bottom-filled casting, while its graphite flakes were also finer in size. In addition, the statistical analysis of non-metallic inclusions using a scanning electron microscope equipped with auto feature analysis software also showed differences in inclusion composition, size, and population density between two castings. The results indicated that the filling turbulence promoted interactions between metal with air, which in turn influenced the formation of non-metallic inclusions. As a result, this impacted the nucleation of flake graphite in the gray iron.

The design freedom of 3D printing allows for new mold designs—not possible with traditional approaches—such as helical sprues and spatially varying lattice castings. However, research on the curing time of printed molds, including the aging, requires more exploration. This study describes the experiments of 3D printed specimens in which embedded environmental sensors were fully encapsulated into sand blocks during an interruption of the binder jetting process. Subsequently, over a 28-day duration, humidity, volatile organic compound (VOC) generation, temperature and barometric pressure were captured for three environmental treatments. Mechanical testing of standard test specimens subjected to the same conditions was conducted. The sand structures held in high (uncontrolled) humidity and at reduced temperature were statistically weaker than a third treatment based on the hypothesis that high humidity and/or low temperatures impede curing.