Fuchu Liu

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.

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.

Effect of Surface Coating Strengthening on Humidity Resistance of Sodium Silicate Bonded Sand Cured by Microwave Heating

The microwave heating sodium silicate bonded sand (SSBS) process is regarded as the most likely molding sand to realize green casting, owing to its low sodium silicate addition, rapid hardening speed, high strength, and excellent collapsibility. However, SSBS can absorb water easily in the air at room temperature. A surface coating strengthening method was used to improve the humidity resistance of SSBS. The properties of SSBS treated by the surface coating strengthening method were compared with that without any treatment. The experimental results indicated that humidity resistance had been improved greatly using the surface coating strengthening method, and comparing to SSBS without any treatment, the compressive strength (σ6h) of the treated SSBS increased 2.32 times and the moisture absorption rate (w6h) can be decreased by 45%. The morphology results revealed that there was a surface coating around the treated SSBS. The linear scanning indicated that the nonhygroscopic coat components presented on the boundary of the treated SSBS, and the surface phase analysis manifested that the boundary of the treated SSBS emerged new three phases, including Al2TiO5, PbTiO3, and NaAlO2, which reduced the free sodium ion content and improved the humidity resistance of SSBS.

Investigation of parameters and mechanism of ultrasound-assisted wet reclamation of waste sodium silicate sands

Abstract In this paper, an ultrasound method was applied in the wet reclamation process, and the feasibility and parameters of the ultrasound-assisted wet reclamation were studied, and the mechanism of the ultrasonic solubilization was also analyzed. The effects of ultrasonic power, time, water consumption, and reclamation times on the de-skinning rate were systematically investigated. The results indicated that the ultrasonic-assisted wet reclamation of the waste sodium silicate sands was feasible. The ultrasonic mechanical effect, cavitation, and thermal effect could accelerate the dissolution of the sodium silicate and improve the de-skinning rate significantly. Orthogonal experiment analysis showed that increasing the ultrasonic power, prolonging the time as well as increasing the water consumption could improve the de-skinning rate. Under the condition of the low water consumption, the de-skinning rate of the ultrasound-assisted wet reclamation reached 90.58%, while the total water consumption was 0.9 t for 1 t of the waste sodium silicate sands.