Zitian Fan

Investigation on the Interface Characteristics of Al/Mg Bimetallic Castings Processed by Lost Foam Casting

The lost foam casting (LFC) process was used to prepare the A356 aluminum and AZ91D magnesium bimetallic castings, and the interface characteristics of the reaction layer between aluminum and magnesium obtained by the LFC process were investigated in the present work. The results indicate that a uniform and compact interface between the aluminum and magnesium was formed. The reaction layer of the interface with an average thickness of approximately 1000 μm was mainly composed of Al3Mg2 and Al12Mg17 intermetallic compounds, including the Al3Mg2 layer adjacent to the aluminum insert, the Al12Mg17 middle layer, and the Al12Mg17 + δ eutectic layer adjacent to the magnesium base. Meanwhile, the Mg2Si intermetallic compound was also detected in the reaction layer. An oxide film mainly containing C, O, and Mg elements generated at the interface between the aluminum and magnesium, due to the decomposed residue of the foam pattern, the oxidations of magnesium and aluminum alloys as well as the reaction between the magnesium melt and the aluminum insert. The microhardness tests show that the microhardnesses at the interface were obviously higher than those of the magnesium and aluminum base metals, and the Al3Mg2 layer at the interface had a high microhardness compared with the Al12Mg17 and Al12Mg17 + δ eutectic layers, especially the eutectic layer.

In house reuse and reclamation of used foundry sands with sodium silicate binder

Abstract Reuse and reclamation of sodium silicate sands have long been of interest because of their unique characteristics in both bonding mechanism and high temperature strength, which make them ideal for applications in cast steel production. After analysis of the characteristics of the used sands containing sodium silicate binder and the requirement for moulding sands, a suggestion is proposed for a sand reuse scheme. Used sands can be reclaimed as support sands after dry treatment or reconditioning, but for use as face sands wet reclamation is necessary. This assertion has been confirmed experimentally on newly developed reclamation equipment. The results showed consistent sand properties and casting quality when applying reused support sands and reclaimed face sands.

Microstructure, tensile properties and fractography of A356 alloy under as-cast and T6 obtained with expendable pattern shell casting process

The microstructure, tensile properties and fractography of A356 alloy were studied under as-cast and T6 conditions obtained with expendable pattern shell casting, and the results were compared with lost foam casting (LFC). The results indicate that α(Al) primary, eutectic silicon and Mg2Si are the main phases in the microstructure of A356 alloy obtained with this casting process. The eutectic silicon particles are spheroidized and uniformly distributed at the grain boundaries after T6 treatment. The average length, average width and aspect ratio of eutectic silicon particles after T6 condition decrease. The sizes of α(Al) primary phase and eutectic silicon of this casting process are smaller than those of LFC. The tensile strength, elongation and hardness of A356 alloy after T6 obviously increase, they reach 260.53 MPa, 6.15% and 86.0, respectively and have a significant improvement compared to LFC. The fracture surfaces of expendable pattern shell casting show a mixed quasi-cleavage and dimple fracture morphology as a

Effect of scanning speed during PTA remelting treatment on the microstructure and wear resistance of nodular cast iron

The surface of nodular cast iron (NCI) with a ferrite substrate was rapidly remelted and solidified by plasma transferred arc (PTA) to induce a chilled structure with high hardness and favorable wear resistance. The effect of scanning speed on the microstructure, microhardness distribution, and wear properties of PTA-remelted specimens was systematically investigated. Microstructural characterization indicated that the PTA remelting treatment could dissolve most graphite nodules and that the crystallized primary austenite dendrites were transformed into cementite, martensite, an interdendritic network of ledeburite eutectic, and certain residual austenite during rapid solidification. The dimensions of the remelted zone and its dendrites increase with decreased scanning speed. The microhardness of the remelted zone varied in the range of 650 HV0.2 to 820 HV0.2, which is approximately 2.3–3.1 times higher than the hardness of the substrate. The wear resistance of NCI was also significantly improved after the PTA remelting treatment.

Effects of Process Parameters on Internal Quality of Castings during Novel Casting

In this study, the A356 aluminum alloy castings were obtained using the expendable pattern shell casting process with vacuum and low pressure (EPSC-VL). The effects of process parameters including gas flow rate, vacuum level, and gas pressure on the internal quality of the castings were investigated through measuring the density and section porosity of castings experimentally as well as computing the porosity defects of the castings by simulation. The results showed that the density of castings increased and the porosity defects of castings decreased with the increase of gas flow rate, vacuum level, and gas pressure, respectively. As a result, the internal quality of castings was greatly improved. The simulation results were in accordance with the experimental results and showed that the trend of splash and turbulence of the molten metal during the filling process increased under the excessively high gas flow rate, which may lead to porosity and oxide inclusion defects. In addition, EPSC-VL process had significant advantages in internal quality, microstructure, and mechanical properties compared to expendable pattern shell casting process under gravity casting (EPSC-G) and lost foam casting (LFC). A complicated and thin-walled aluminum alloy part with high quality has been successfully manufactured using this technology.

Influence of process parameters on filling ability of A356 aluminium alloy in expendable pattern shell casting with vacuum and low pressure

Abstract The influence of process parameters, including casting temperature, gas flowrate, vacuum level and gas pressure, on the filling ability of A356 aluminium alloy in expendable pattern shell casting process with vacuum and low pressure (EPSC-VL) was investigated in moulds of different thicknesses. It was found that the effect on the filling ability of A356 alloy is in the following order (from strong to weak): gas flowrate, casting temperature, gas pressure and vacuum level. The filling length was found to increase with the increase in all the process parameters, and the relationship between the filling length and the process parameters is almost linear. Moreover, the EPSC-VL process is shown to have advantages in filling ability and internal quality compared with expendable pattern shell casting under gravity and lost foam casting. A high quality complex thin walled part has been successfully produced using the EPSC-VL process.

Use of Spark Plasma Sintering for Fabrication of Porous Titanium Aluminide Alloys from Elemental Powders

Porous titanium aluminide alloys were fabricated by spark plasma sintering (SPS) plus postheat treatment from titanium and aluminum elemental powders using sodium chloride as the space holders. Various interconnected porosities were achieved by SPS at 600°C/10 MPa, followed by water dissolution to remove sodium chloride. The phase transformation between titanium and aluminum, however, was not accomplished. Two kinds of postheat treatment, pressureless SPS and vacuum annealing, were employed to obtain the phase transformation. Results showed that most of the pores formed before were retained and the phase transformation, formation of γ and α2 phases, were completed during vacuum annealing. Whereas a great deal of pores were disappeared after pressureless SPS.

Research on Humidity Resistance of Sodium Silicate Sand Hardened by Twice Microwave Heating Process

To study the high moisture absorbability of the sodium silicate boned sand hardened by microwave heating, a new special water-based coat sprayed on the surface of the sand samples hardened by the first microwave heating and then sintered by the second microwave heating to form a compact coating layer was studied. The results showed that humidity resistance of the sand samples with the coating layer had great improvement compared to the sand samples without the coating layer, the compression strength (σ 4h ) of the sand samples with the coating layer increased 2.62 times than that without the coating layer. Scanning electron microscope (SEM) and X-ray diffraction (XRD) have been used to investigate phase and composition of the compact coating layer. The SEM analysis showed that the coated sand samples formed the compact layer which could greatly improve humidity resistance of the sand samples. The line scanning analysis confirmed that the coat composition appeared on the surface of the coated sand samples, and the surface XRD analysis demonstrated that the surface of the coated sand samples consisted of four new phases, including PbTiO3, NaAlO2, Pb6Al2Si6O21 and Al2SiO5, which are the main materials for increasing humidity resistance.

Microstructure and Mechanical Properties of Ductile Cast Iron in Lost Foam Casting with Vibration

The microstructures and mechanical properties of the ductile cast iron (DI) specimens obtained by lost foam casting ( LFC) with and without vibration were investigated. The results indicate that the number of the graphite nodule increases from 175 mm−2 of the specimens produced by LFC without vibration to 334 mm−2 of the specimens produced by LFC with vibration, and the thickness of the ferrite shell increases. Meanwhile, the amount of the carbides decreases in the specimens produced by LFC with vibration and the granule structure then forms. These are mainly attributed to the “crystal shower” caused by the vibration. In addition, the tensile strength and elongation of DI specimens produced by LFC with vibration are improved due to the dispersion-strengthening of refined carbide and pearlite colony, uniform distribution of the graphite nodule, and increase of the amount of dimples and tearing edges.

Microstructural evolution of Mg9AlZnY alloy with vibration in lost foam casting during semi-solid isothermal heat treatment

Abstract The nearly equiaxed grains of Mg9AlZnY alloy were obtained by vibrating solidification in lost foam casting(LFC) and the microstructure of Mg9AlZnY alloy was analyzed. On this basis, the morphology and size of α-Mg grains fabricated by semi-solid isothermal heat treatment(SSIT) at 530 ? and 570 ? holding different time were studied. The results show that the main constituent phases of Mg9AlZnY alloy are α-Mg, β-Mg 17 Al 12 and Al 2 Y, and the Y can greatly refine α-Mg grains. The distribution of α-Mg grains equivalent diameters between 20 and 100 μm is up to 87%, and the average roundness of α-Mg grains reaches 1.37 in the specimen obtained at 570 ? and holding time 60 min. According to the analysis of solidification kinetics and thermodynamic, binary eutectic with low melting point melts firstly on SSIT process. As the liquid fraction increases with the solute diffusibility, both of the shape and size of α-Mg grains change ceaselessly. When the liquid fraction reaches equilibrium, the α-Mg grains are gradually spheroidized under the interfacial tension, and then the α-Mg grains begin to combine and grow. Evolution of α-Mg dendritic grains on SSIT process is obviously different from that of equiaxed grains.