International Journal of Metalcasting最新文献

Thermal conductivity is an important property for cast components produced from different types of cast iron. Development of a general widely-accepted thermal conductivity model for compacted and lamellar graphite irons poses a research challenge. The present study extends the modeling approach introduced earlier for pearlitic lamellar graphite iron toward compacted graphite iron and ferritic lamellar graphite iron. The proposed thermal conductivity model of the bulk material is based on the alloy microstructure and Si segregation between eutectic cells and non-cell regions, at the main assumption that the heat paths in the eutectic cells are formed by connected graphite phases surrounded by ferrite phases. The overall thermal resistance of these heat paths is determined by the hydraulic diameter of the interdendritic region. The uncertainties both for the modeled and for experimentally derived thermal conductivities have been estimated. The importance of considering the Si segregation in the model has been discussed. For the investigated samples, the agreement between modeled and measured thermal conductivities has been achieved within 4% on the average, at the same value of the single fitting parameter found for pearlitic, pearlitic–ferritic lamellar, and compacted graphite iron alloys. The results contribute to the understanding of the material microstructure effects on the cast iron thermal conductivity.

High-temperature melting experiments (1600 °C), metallographic microscopy and scanning electron microscopy were used to investigate the morphology, quantity and size of TiN in the center of high-titanium high-strength steels under different Mg content (0 wt.% → 0.0023 wt.%). The results showed that based on thermodynamic calculations regarding the aluminum-magnesium content relationship during deoxidation product formation, significant amounts of MgAl₂O₄ are generated even with trace amounts of Mg present in the tested steel. The solidification structures of all tested steels are equiaxed grains when the solidification cooling rate is 0.17 °C/s. The average size of equiaxial grain in the tested steels decreased from 320 to 271 μm, 195 and 101 μm as the Mg content increased from 0 to 0.0007 wt.%, 0.00014 and 0.0023 wt.%, respectively. MgO and MgAl₂O₄ precipitate before TiN and have a small lattice mismatch with TiN (0.02 and 5.03%, respectively). As the Mg content in the steel increased from 0 to 0.0007 wt.%, 0.0014 and 0.0023 wt.%, the areal density of TiN in the tested steels increased from 44.4 to 102.4 No./mm², 129.4 and 144.2 No./mm², the maximum size of TiN particles decreased from 16.5 to 10.4 μm, 9.8 and 9.3 μm, the average size of TiN decreased from 9.1 to 4.2 μm, 3.3 and 3.1 μm, and the proportion of TiN precipitated at the grain boundaries decreases from 22.7 to 16.8%, 14.5 and 14.8%, respectively.

This research work reports on the mechanical and sliding wear performance analysis of vacuum-cast AA7075-Co (0–2 wt% @step of 0.5) alloy composites for gear application. The specimens were sized for their physical, mechanical, and sliding wear test standards. Wear tests were performed in lubricated conditions on a muti-specimen tribo-tester. The results show that reinforcement of cobalt particulates into the alloy matrix improves the mechanical properties and reduces the void content. The resultant composites have density ranges from 2.81 to 2.91 g/cc, voids content from (~ 3.55 to 2.46%), hardness from 151.2 to 196 Hv, flexural strength from 341 to 498.2 MPa, compressive strength from 290 to 490 MPa, tensile strength from 235 to 394 MPa, and impact strength from 20 to 65.5 J. The specific wear rate shows a 25% improvement in performance with cobalt reinforcement relative to neat one. The Taguchi analysis with ANOVA reveals the following parametric order of normal load, sliding velocity, sliding distance, and filler content that actively controls the wear process of such composites. Further, Preference selection index ranking methods reveal that the composition having 2 wt% cobalt reinforcement tends to optimize overall performance metrics relative to others and has validated with subjective analysis.

The present work was performed on experimental Al–Si near eutectic cast alloys, with different additives mainly Fe, Mg, Mn, Cr, Sr and P. The alloys were solidified at 0.8°C/s, very close to equilibrium conditions. Precipitated phases, primarily Fe-, Cu-, Mg-, and Sr-based intermetallics, were examined. Although the phases reported in the present work were documented previously, the range of chemical composition of each phase was confirmed using an electron probe microanalyzer (EPMA) equipped with wavelength dispersive spectroscopy (WDS) and electron dispersive X-ray spectroscopy (EDS) facilities. Some of these alloys were cast in the form of hardness test pieces using a steel permanent mold preheated at 425 °C that provided a microstructure with an average dendrite arm spacing (DAS) of ~22 µm. The test pieces were solution heat treated at 500 ± 2 °C for times up to 24 h, followed by artificial aging at 155 °C for 5 h (T6 treatment). Hardness tests were carried out on the heat-treated test pieces. It was found that addition of Sr decreased the hardness. The role of P addition (AlP) on the nucleation of primary Si particles has been discussed. Although the addition of P in terms of 30 ppm leads to refining of the primary Si particles, the P-Sr interaction has a marked negative effect of the modification of the eutectic Si particles.

In this paper, x wt.% Mg₂Si/Al–5 wt.% Cu (x = 5, 10, 15, 20, and 25) composites were prepared by an in situ process. The effect of phase content of Mg₂Si on their microstructures and performances was investigated; the dry sliding wear behavior under room temperature was examined. The results show that with the increase in Mg₂Si (Mg and Si) concentration, the microstructure of the Al–Mg₂Si composite changes significantly. The eutectic microstructure changes from lamellar labyrinth to long rod, along with the long-range order Al₂Cu phase to island and plate-like morphology, and the primary Mg₂Si phase becomes more compact. The hardness increases from 117 HV to 163 HV. The friction coefficient, wear rate, wear width, and wear depth decrease from 0.368 ± 0.048, 2.7 × 10⁻⁵ mm³/m, 1.93 mm, and 133.3 μm to 0.315 ± 0.016, 1 × 10⁻⁵ mm³/m, 0.94 mm, and 70.2 μm, respectively. The tested composites worn surfaces exhibit adhesion, peeling, microcutting wear, abrasive, and oxidation.

The focus of this work is the effect of heat treatment temperature upon the microstructure, hardness, wear and friction of high manganese steel produced in an industrial setting. The obtained steels were subjected to two heat treatments, one at 1050 °C and the other at 1100 °C followed by water quenching. The microstructures were characterized by optical microscopy and scanning electron microscopy equipped with an energy-dispersive spectrometer. Rockwell C hardness and Vickers microhardness were also measured. Wear behavior in dry conditions was investigated under a load of 300 N using pin-on-disk method. Tribological behavior in boundary lubricated conditions under a load of 60 N at high temperature (100 °C) was studied using a custom-made reciprocating tribometer by measuring the mass loss and the friction coefficient. A 5W-40 engine oil was used as lubricant. Atomic force microscopy (AFM) analysis and roughness 2D and 3D of the tested samples were measured. The obtained results showed that in the as-cast state, the added elements favored the formation of simple or complex inter- and intragranular carbides. In the heat-treated state, the microstructure of the examined steels consists of retained austenite, martensite and precipitates. Increasing of heat treatment temperature increases the rate of the formed martensite. Formation of secondary carbides and increasing of martensite amount led to the improvement of hardness and wear resistance.

In the present work, the effects of Dy (dysprosium) additions (0, 0.05, 0.1, 0.15, 0.2, and 0.3wt%) on the microstructure and mechanical properties of hypereutectic Al–Si alloy have been studied. An inductively coupled plasma optical emission spectrometry (ICP-OES) apparatus was employed to measure the alloy composition. The specimens were examined using optical microscopy (OM) and scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS). In the as-cast state, increasing the Dy content to 0.15% resulted in the refinement of the primary Si morphology from irregular polyhedral and branched shapes to fine polyhedral shapes, with the average size decreasing by 21% from 48 to 38 μm. Additionally, the eutectic Si transformed from coarse, uneven short rod-like structures to fibrous ones. Moreover, the tensile strength increased to 233 MPa, marking an 18.8% improvement, while the elongation reached 1.1%, indicating a significant increase of 267%. After T6 heat treatment, with a Dy content of 0.2%, the size of primary Si and eutectic Si did not change significantly compared with the 0.15% Dy addition. However, the mechanical properties of the alloy were optimized at this Dy content due to the fragmentation of the Al–Si-Fe-Mn phase and Al2Cu phase. The tensile strength increased to 242 MPa, reflecting a 14.7% improvement, and the elongation improved to 1.28%, representing a 60% enhancement compared with the alloy without Dy addition.

Graphical Abstract

A numerical time integration procedure for the calculation of the secondary dendrite arm spacing (SDAS) in FeC hyper-peritectic alloys is presented, a preferred group of low-carbon casting steel. The procedure incorporates a three-stage thin arm dissolution model, which is solved at each time step using Newton–Raphson iteration. This is coupled to a coarsening model based on the integral forms of the dissolution model, which are solved using Gaussian quadrature, as well as a growth model for solid fraction evolution. The procedure can easily be embedded into numerical models for solidification, in which the space–time evolution of the SDAS is required for determining the dynamic permeability in the mushy zone. Higher order approximations for both growth and solute concentration evolution can easily be incorporated. Temperature dependence of thermophysical parameters is taken into account using inter-dendritic solidification empirical models, and an alloy-specific peritectic reaction constant is used to determine the isothermal peritectic holding time. The procedure is validated against experimental data presented in literature. Various cases of SDAS as a function of local solidification time, cooling rate and carbon composition are investigated. The method is compared to experimental results of SDAS obtained from test castings of a hyper-peritectic steel alloy and can be used to iteratively determine the alloy-specific peritectic reaction constant by comparing the solid fraction evolution during the peritectic reaction with that found from the experimental cooling curve.

In the sand casting process, molten metal needs to reach all parts of the mold cavity uniformly and smoothly. This requires the use of multi-gate systems with an optimal design to ensure balanced flow through all gates. For this purpose, a novel experimental design presented by the authors in earlier studies was modified to accommodate the geometric variation of gating elements, realized through a robust design approach. Water was used to perform experiments on flow through the horizontal multi-gate system using a standard orthogonal array. The analysis of the results of each parameter on the influence of flow balancing was studied using Taguchi’s analysis of mean (ANOM) and analysis of variance (ANOVA). The most important factors and their best combination of settings influencing flow balancing were predicted for the water model experiments. Using a full factorial design, an interaction study was performed and compared with the main factor effects. Although there was a slight interaction between one set of factors, no change in dominant factors was found. Further validation experiments were performed using cast iron. The comparison of water and metal flow demonstrated that the two fluids have different dominant factors influencing multi-gate flow balancing.

Al–Si–Cu–Ni–Mg–(Zr, Sr) alloys were prepared by permanent mold gravity casting. The effects of Zr and Sr on the microstructure and mechanical properties of cast Al-12Si-6Cu-1.5Ni-1.3Mg alloy at room temperature and high temperature were investigated systematically using X-ray diffractometer (XRD), ultra-depth-of-field metallographic microscope, scanning electron microscope (SEM), transmission electron microscope (TEM) and electronic universal testing machine. The experimental results show that the size of eutectic Si phase and Al–Cu–Ni phase is decreased with the addition of Zr, and it has little effect on the primary Si phase. The massive primary Si phase of the alloy with 0.1%Zr + 0.04%Sr addition disappears, and the eutectic Si phase changes from acicular to fibrous phase, which has little effect on the size of the Al–Cu–Ni phase. The ultimate tensile strength, yield strength and elongation of the alloy with 0.1%Zr + 0.04%Sr addition at room temperature are 360 MPa, 318 MPa and 4.2%, respectively. The ultimate tensile strength and elongation of the alloy with 0.1%Zr addition at high temperatures are 194 MPa, 4.3%, 117 MPa, 7.5% at 275 °C and 350 °C, respectively.