International Journal of Metalcasting最新文献

The current study is aimed to enhance the tensile performance of Al–Si–Cu–Mg cast alloys at both ambient and elevated temperatures. The investigation is focused on incorporating zirconium (Zr) as a primary alloying element, alongside nickel (Ni) and manganese (Mn), to assess their suitability for automotive engine applications. In Mn-containing alloys, tensile strength improvement was observed due to the precipitation of compacted α-Al₁₅(Fe, Mn)₃Si₂ and Al₆Mn phases. Meanwhile, Ni-bearing phases such as Al₃CuNi and Al₃Ni in Ni-containing alloys were found to inhibit crack propagation, thereby enhancing tensile properties. Results indicated that the addition of 0.75 wt.% Mn yielded comparable strength values to alloys containing 2–4 wt.% Ni at ambient temperature. Additionally, the presence of 0.25% Zr facilitated the precipitation of fine metastable L1₂-Al₃Zr particles, contributing to improved alloy strength. However, the introduction of 4% Ni resulted in the formation of Al–Cu–Ni particles rather than Al₂Cu, leading to a decrease in alloy strength upon aging.

Gas generation from molding materials creates a complex atmosphere in the mold–metal interface and is one of the primary causes of defects in cast components. Moisture, crystalline water, and decomposing binders are significant gas sources. The presence of volatiles and decomposing binder in the mold also affects the rate of heat absorption from the solidifying metal during the casting process. This work presents a measurement methodology to evaluate the rate and volume of gases generated from sand mixtures in combination with the temperature distribution and applied thermal analysis. The presented results show high reproducibility of the method. The thermal analysis results provide the start and end temperature of the binder decomposition reactions and the corresponding heat absorbed in this interval. The results obtained from the presented methodology can be used to validate the models/simulation tools developed to predict the gas evolution and related transport phenomena in the sand casting process.

This study explores the effect of bismuth on ductile iron to enhance its mechanical properties and to prevent the formation of chunky graphite. Various heats of ductile iron were produced with varying bismuth (0.000–0.010 wt%Bi). Microscopic examinations, Brinell hardness tests, and tension tests were conducted to characterize the samples. The results indicate that Bi influences the microstructure, nodule count, hardness, and tensile strength of the ductile iron, with optimal amount of Bi (0.005–0.007 wt%Bi) depending on section thickness. Bi prevented the carbide formation and increased the nodule count, leading to improved mechanical properties. In addition, the study demonstrated that Ce/Bi values of 1.29–1.60 were corresponding levels that showed optimal microstructure and properties. Thermal analysis demonstrated the inoculation effect of Bi addition by shifting TE_low and TE_high toward the stable eutectic temperature. Electron Probe Microanalysis (EPMA) results showed that Bi oxide and sulfide were found at the graphite cores as heterogeneous nucleation sites during solidification.

The primary objective of this investigation is to strengthen the mechanical and tribological properties of the cast Elektron 21 alloy (UNS M12310) by reinforcing its surface with a high entropy alloy (HEA) consisting of 0.3 wt% aluminum, 0.3 wt% copper, 0.1 wt% nickel, 0.1 wt% silicon, and 0.2 wt% tungsten fabricated by friction stir processing (FSP). The resulting Elektron 21/HEA surface composites (SCs) processed through casting followed by FSP were compared to the cast followed by FSPed Elektron 21 alloy, exhibiting significant enhancements in mechanical properties and wear resistance. The surface of the Elektron 21 matrix, which underwent casting followed by FSP, showed a homogeneous dispersion of HEA particles. These particles served as precipitates, creating geometrically necessary dislocations that hindered movement under applied force. The bonding between the HEA and the Elektron 21 alloy at the interface was excellent, and differential thermal contraction resulted in a strain misfit. Consequently, the microhardness, yield stress, and ultimate tensile stress of the FSPed Elektron 21/HEA SCs improved by 38%, 37%, and 32%, respectively, compared to the FSPed Elektron 21 alloy, although ductility decreased by 33%. Furthermore, the FSPed Elektron 21/HEA SCs showed a 33% enhancement in wear resistance and a 27% reduction in frictional force generation compared to the FSPed Elektron 21 alloy. The worn surfaces of the FSPed specimens showed that the FSPed Elektron 21 alloy revealed deep grooves, pits, micro-cutting, micro-grooving, and ploughing, while these features were absent in the FSPed Elektron 21/HEA SCs. These outcomes make it better suited for use in the aviation and automotive sectors.

Graphical Abstract

Binder Jetting technology is well established for the production of sand molds and cores for foundry use, owing to its flexibility and expansive design capabilities. A wide array of sand, aggregate, and binder combinations is commercially available. Utilizing these types of refractory materials in the casting process presents both technical and economic benefits and drawbacks. For intricate cast components, foundry technologists must assess the thermophysical properties of the mold material systems. With this knowledge, specialized high-performance material combinations may be employed in specific areas of the mold, while more economically viable systems are used for shaping the external mold support. This study primarily focuses on determining the heat capacity and thermal diffusivity and consequently the thermal conductivity using a specially developed analytical method. It investigates three different fundamental aggregates: silica, cerabeads^®, and chromite. The result’s range provides an overview of relevant characteristics for the selected material systems. Given that the properties of sand affect heat flow during casting and solidification, these newly determined values can be utilized in future simulations. Consequently, these findings aid in maintaining and enhancing the quality of critically stressed cast parts.

A dual-phase cast steel with high silicon content has been developed to resist low-stress abrasive wear. The alloy is composed of Fe–0.3C–2.5Si–0.5Cr–0.3Mo–0.1Nb, and the Y block was produced using an investment casting process with an induction melting furnace. Following casting, the block was homogenized and subjected to intercritical annealing heat treatments at 825, 850, and 875 °C before being tempered at 350 °C. The microstructure of the specimens was studied by using optical (OM) and scanning electron microscopy equipped with image analysis software and an energy-dispersive X-ray spectroscopy analyzer. Mechanical properties were evaluated using Vickers hardness and tensile tests at room temperature. The tribological behavior of the specimens was determined using the pin-on-disk wear test method with abrasive paper at a force of 20 N (0.6 MPa). The results showed that the microstructure of the intercritical annealed steels consisted of polygonal and acicular ferrites and tempered martensite accompanied by niobium carbide. The martensite volume fraction, hardness, and yield strength increased with increasing IA temperatures, but the tensile strength remained relatively stable. Additionally, the tribological investigation indicated that the optimal wear resistance was achieved at 850 °C, and micro-cutting was the primary wear mechanism.

For the spheroidal graphite cast iron materials, also known as ductile cast iron (DCI), EN-GJS-400-18-LT and EN-GJS-450-18, different welding procedures were examined for potential repair welding. A repair weld was performed on thick cast iron plates using the optimum procedure in each case. The weld was evaluated for all areas of the welded joint (weld metal, fusion line/heat-affected zone and base metal). In addition to the metallographic microstructural analysis, the characterization of the repair weld was carried out by means of hardness distribution measurements, static tensile testing and notched bar impact testing as well as fracture mechanics investigations under static and under cyclic loading in a wide load ratio range. On this basis, a generalized description of cyclic crack growth could be made according to the NASGRO® MODEL. NASGRO® is a fracture mechanics and fatigue crack growth software. In accordance with the possible operating conditions of repair-welded, thick-walled components, the static and impact tests were performed in the temperature range down to (-)40 ({}^{circ }text {C}).

In this paper, four different casting materials were used to get gray cast iron samples, the effects of different cooling rates caused by different casting materials on graphite distribution, matrix structure and mechanical properties were investigated. The experimental results show that as the cooling rate increases, the graphite form of gray cast iron changed from coarse flake A-type graphite to rosette shaped B-type graphite, graphite increased in quantity and was more evenly distributed. The interlayer spacing of pearlite in matrix decreased with the increase of cooling rate, four different mold casting of cast iron material sample of pearlite lamellar spacing is CO₂ sodium silicate bonded sand mold, 340 nm, oxide ceramic mold, 275 nm, cast iron mold, 141 nm, graphite casting mold, 135 nm, respectively. The reduction of the interlayer spacing of pearlite also significantly improves the tensile strength, compressive strength and hardness. The tensile strength of cast iron specimens cast in graphite casting molds is the highest, at 421 MPa, while the tensile strength of cast iron specimens cast in CO₂ sodium silicate bonded sand molds is the lowest, at 346 MPa. The graphite cast iron sample has the highest compressive strength of 2165 MPa, and the oxide ceramic cast iron sample has the lowest compressive strength of 1115 MPa. The Brinell hardness of the samples cast in cast iron molds is the highest, at 409 HB, while the samples cast in CO₂ sodium silicate bonded sand molds have the lowest Brinell hardness, at 255 HB. In addition, increasing the cooling rate inhibited the diffusion of elements in the melt, reduced the final solidification interval and also reduced the shrinkage porosity and other defects. Fracture analysis shows that cleavage fracture is the main fracture mode of castings. The higher the cooling rate, the smoother the fracture morphology.

From the perspective of reducing the carbon footprint, yield improvement is seeing global interest. One possibility to achieve this goal is to influence the volume of feed metal in the molds to achieve a sound casting. The largest volumes of risers are used in steels, so the research has focused on carbon steels for castings. Typically, to reduce the amount of molten metal in the riser, sleeves are used, such as exothermic and insulating ones. However, this is no longer sufficient, and therefore, blends of sleeves have been developed that perform both exothermic and insulating functions. The use of a new and innovative two-layer sleeves, combining the advantages of both layers (inner layer exothermic, outer layer insulating), proves to be highly effective. The conducted experiment compares this new approach with commonly used sleeves (exothermic, insulating, and exothermic—insulating). The utilization of riser metal using the new two-layer sleeve showed to be 8–10% higher compared to standard exo—iso mixed sleeves, and compared to single-layer inserts, the utilization of molten metal was 18–20% higher.

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.