International Journal of Metalcasting最新文献

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.

This study aims to assess the influence of the Mn to S ratios on the machinability and tensile behavior of GG20-gray cast iron brake drums. The effect of various Mn and S contents on microstructural characteristics such as type, size, and aspect ratio of graphite particles, interlamellar spacing of pearlite, and the distribution factor, size, and volume fraction of MnS were investigated. The microstructural results showed that a decrease in the Mn/S ratio to 5.1 and a decrease in the Ti/S ratio to under 0.11 promote the lengthy A-type graphite formation. Meanwhile, with the %Mn × %S value of about 0.08, the best uniform distribution of MnS inclusions has been obtained (about 55% of MnS inclusions are near A-type graphite flakes in the P1 specimen with %Mn × %S about 0.08 and Mn/S value of 5.1). Good machining in terms of less wear of the cutting tool and easier fragmentation of the chip in the sample with Mn/S value of 1.5 (0.65% Mn and 0.128% Sulfur) due to having more MnS inclusions, as well as a larger grain size graphite and its high aspect ratio have been obtained. The minimum tensile strength has been calculated to be 193MPa in the specimen with Mn/S value of 3.5 (0.55% manganese and 0.156% sulfur) due to the effects of higher sulfur content on changing the morphology of graphite to a higher aspect ratio. Meanwhile, at the same content of Mn (almost 0.55 wt%), further reduction of sulfur results in promoting E and D types of graphite in the microstructure.

Graphic Abstract

In this study, the in-situ ZrB₂/Al-Si5Cu3 aluminum alloy composites were fabricated through the salt-melt reaction route with different weight fractions of ZrB₂ reinforcements, i.e., 2.5%, 5%, and 7.5%. The composites were tested for their density, hardness, tensile strength, flexural strength, impact strength, and wear properties. The influence of reinforcement on the properties was studied concerning the wt.% of reinforcement. The increase in density of composites compared to the matrix material confirms the formation of the in-situ reinforcement phase. The microstructure showed a desirable distribution of reinforced particles over the matrix at all weight fractions of the reinforcements in the composites. The ZrB₂ particles formed in the matrix have particle sizes in the range from 255 nm to 955 nm and the grain size has been reduced from 242 microns to 110 microns as the result of particle-induced solidification. The hardness of the composites containing ZrB₂ reinforcements of 2.5, 5, and 7.5 wt.% showed improvement by 8%, 17.5%, and 34% respectively compared to the parent alloy. There is an improvement in the tensile strength and elongation for the wt.% of ZrB₂ up to 5 wt.%, from 115 MPa to 183 MPa, after which, there was a drop in the tensile strength. The detailed analysis of tensile fractography shows that the agglomerated ZrB₂ reinforced particles at higher weight fractions lead to a decrease in strength. The results of flexural strength also affirm the strength of 5 wt.% ZrB₂/Al-Si5Cu3 increased from the matrix material’s flexural strength of 337 MPa to 672 MPa. The wear study shows that the composite with 7.5 wt.% ZrB₂ possesses a higher wear resistance. However, the impact strength did not show any differences in the weight % of reinforcement.

Vortex-free high-speed stir casting (VFHSC) methodology can achieve uniform dispersion of particles in melt without air entrapment for fabricating particle reinforced composites, and it has been proved to be feasible for preparing micron-composites by this methodology. In this work, in order to study deeply on particles in nano-size magnitude in composites by this methodology, the preparation of 1.5 vol.% Nano-Al₂O_3p/Al–Cu–Mg–Si composite is also investigated. The proper stirring parameters for ideal particle dispersion are determined to prepare the materials. Porosity of the composite can be limited to 0.147 % under the VFHSC methodology. The composition and microstructure of ingots, including the incorporation of Al₂O₃ particles as well as the morphology of precipitated phases, are examined by OM, XRD, SEM, TEM, HRTEM and EDS. The nano-particles are incorporated ideally in the matrix with restricted aggregation and sedimentation, and the well-bounded Al₂O₃–Al interface possesses semi-coherent interface. Moreover, the VFHSC 1.5 vol.% Nano-Al₂O_3p/Al–Cu–Mg–Si composite exhibits obvious strengthening, limited ductility reduction, higher hardness as well as better wear resistance than those of matrix, validating the efficacy of the VFHSC methodology on fabricating 1.5 vol.% Nano-Al₂O_3p/Al–Cu–Mg–Si composite. The work proves that incorporating nano-particles in Al matrix by VFHSC methodology is feasible and efficient. The work presented in this paper proposes a viable approach for the fabrication of nanocomposites using the stir casting method, thereby offering valuable insights for further research on stir casting technology.

The hybrid aluminium alloy matrix composites are adopted in high-strength-to-weight ratio applications with technical benefits, including high strength, good hardness, better stability, and improved thermal stability. This research is enhancing microstructural and mechanical functional behaviours of the hybrid aluminium alloy (AA2024) nanocomposites by the blending actions of nano silicon carbides (SiC) particles and multi-walled carbon nanotube (MWCNT) via a two-step stir cast route. The contribution effect of SiC and MWCNT blending actions on metallography, physical/mechanical qualities, and resistance to corrosion individualities of hybrid AA2024 nanocomposites are studied by the procedure of the American Society for Testing and Materials (ASTM) and compared to monolithic cast AA2024 alloy characteristics. The hybrid AA2024 nanocomposite blended with SiC and MWCNT (weight percentages of 5 and 8%) exposed the specific tailored benefits like homogenous scattered reinforcements resulting in a lower percentage value of porosity (≤ 1%), excellent ultimate tensile strength of 330 MPa with acceptable elongation range of 10%, enhanced indentation resistance capabilities of 128 HV, specific toughness of 15.2 J/mm², and enhanced corrosion performance.