International Journal of Metalcasting最新文献

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.

In this paper, microstructure, mechanical properties and wear resistance of as-cast Mg-3Al-1Ca-0.4Mn/Tip magnesium matrix composites were investigated. As-cast Mg-3Al-1Ca-0.4Mn/xTip (x = 0, 1, 2, and, 3wt%) composites were prepared using a combination of mechanical stirring and permanent mold casting. The results showed that nanoscale interfacial products (Al₂Ti phases) were precipitated at Ti/Mg interfaces, which contributed to the formation of strong interfacial bonding. Compared with matrix alloys, Mg-3Al-1Ca-0.4Mn/2Tip composites had better mechanical properties and wear resistance with ultimate tensile strength, yield strength, elongation, hardness and wear rate of 149 MPa, 86 MPa, 8.6%, 46 HBW and 8.4×10^-3 mm³/(N m), which indicated significant improvements of 26%, 38%, 36%, 10% and 59% over the Mg-3Al-1Ca-0.4Mn alloys, respectively. Grain refinement, load transfer and strong interfacial bonding all had important effects on improving mechanical properties of composites. The increased wear resistance of composites was mainly attributed to the incorporation of high hardness phases and the formation of protective oxide films.

The cast AlSi₁₂CuNiMg alloy finds broad applications in automotive components. The manufacture of defect-free castings, especially for long, thin-walled structures, requires an understanding of filling properties. The main aim of this investigation is to understand the fluidity of an AlSi₁₂CuNiMg alloy in a multi-spiral channel with varying thickness through the casting simulation and validate it through casting experimentation. Furthermore, the effect of pouring temperature and section thickness on fluidity was investigated, and an optical microscopy was carried out for microstructure observation. The results showed that the flow length (L) of the alloy increased with increasing pouring temperature (T) and decreased with a reduction in the section thickness. In order to predict the fluidity of AlSi₁₂CuNiMg alloy obtained from the spiral tests, mathematical models ( (L_text{f} = - 705 + 1.044 T + 46.17 x)) were developed based on the functional relationship between the fluidity and casting parameters by fitting the fluidity data. The simulation results show good agreement (91%) with the fluidity length obtained in the experimental study. The benchmark can also be used to develop the fluidity database of different alloys for thin sections.

In the article, the authors present results of microstructural studies of Al-Mg-Si-Mn casting alloys with Zr, Li, and TiB₂ additions on a broad scale. Zirconium content was set on two levels: 0.34 and 1.58 wt%, and Li was set 1.2 and 2.0 wt%. It was found that the addition of Zr shifts the eutectic melting temperature to a higher level, up to 611.3 °C at 1.6 wt% Zr. At the same time, Li addition leads to the depression of eutectic melting temperature: down to 587.2 °C at 2.0 wt% Li, what is a common effect of eutectic modification which was confirmed by means of structural examinations. The complex addition of Li and AlTi5B1 resulted in a eutectic melting temperature close to the equilibrium eutectic temperature for the Al-Mg-Si system (596.2 °C). The grain refinement effect of Zr is due to the nucleation of α-Al on the Zr(Al_1−x, Si_x)₃ phase. Crystals of this phase were detected in the grain centers of Zr-containing alloys. The Li addition does not affect α-Al grain size but changes the morphology of eutectic colonies from petal-like to fibrous. Observation of TiB₂ particles inside the primary Mg₂Si crystals gives direct experimental confirmation of nucleation of the primary phase on the surface of TiB₂ in the alloy after adding Li and AlTi5B1. Natural aging of the alloys resulted in the formation of fine precipitates detected close to dislocations. The most apparent supposition is that the mechanism responsible for their formation is heterogeneous nucleation in the stress field of dislocations. Hardness tests showed adding 2.0 wt% of Li is very effective, increasing hardness up to 113 HV0.2 in naturally aged condition, which is nearly double that of commercial Al-Mg-Si die-casting alloy. Several effects were proposed which may synergistically contribute to the rise of hardness in Li-containing alloys, such as solid solution strengthening, formation of primary LiAlSi phase and natural aging.

The effect of Sb addition on the hot tearing susceptibility (HTS) of Mg–7Al–1Ca–xSb (x = 0, 0.5, 1, 1.5, and 2 wt.%) alloys was studied using a “T-shaped” hot tearing measuring system and differential thermal analysis experiments. The mechanical properties of the alloys were investigated using tensile tests. The crystal phases of the alloys were analyzed by X-ray diffraction and energy-dispersive X-ray spectroscopy. The microstructure and the morphology of the crack zone and the tensile fracture were characterized by optical microscopy and scanning electron microscopy. The results showed that the HTS of the alloys first decreased with Sb addition up to 1.5 wt.% and then displayed an increase with Sb addition up to 2 wt.%. The addition of Sb refined the structure, made the distribution of the second phases more homogeneous, and improved the skeleton strength, thereby reducing the HTS of the alloys. However, when the Sb addition reached 2 wt.%, the low-melting-point eutectic phases that could participate in feeding reduced, resulting in an increase in the HTS of the alloy. Additionally, the mechanical properties of the alloys were improved after adding Sb. Among them, Mg–7Al–1Ca–1Sb alloy exhibited the optimal ultimate tensile strength, yield strength, and elongation with the values of 203 MPa, 133 MPa, and 8%, respectively.