Wenming Jiang

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.

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

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.

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.

Effects of Mechanical Vibration and Wall Thickness on Microstructure and Mechanical Properties of AZ91D Magnesium Alloy Processed by Expendable Pattern Shell Casting

Mechanical vibration was introduced into the solidification process of AZ91D magnesium alloy during the expendable pattern shell casting process, and the combined effects of mechanical vibration and wall thickness on the microstructure and mechanical properties were investigated. The results indicate that with the increase of wall thickness, the morphologies in α-Mg phase and β-Mg17Al12 phase of the samples obtained without vibration evolved from a fine dendrite to a coarse dendrite and from a fine continuous network structure to a coarse continuous network structure, respectively, and the mechanical properties and density of AZ91D alloy continuously decreased. With the application of mechanical vibration, the coarser dendrites transformed into fine equiaxed grains, and the previous coarse continuous network structure of the β-Mg17Al12 phase was changed to a discontinuous granular morphology. Meanwhile, the mechanical properties and density of AZ91D alloy greatly increased. The effect of mechanical vibration on the microstructure and mechanical properties increased with increasing vibration frequency and wall thickness. The fractographs of the tensile samples show a change in fracture surface from brittle to that of a tough fracture with the addition of vibration.

Microstructure of Al/Al bimetallic composites by lost foam casting with Zn interlayer

ABSTRACT A novel method named the lost foam casting (LFC) liquid–liquid compound process with a Zn interlayer was proposed to prepare the Al/Al bimetallic composites, and the microstructure of the Al/Al bimetallic composites was investigated in the present work. The results showed that the Al/Al bimetallic composites were successfully produced using the novel process. The Zn interlayer prevented different liquid metals from directly mixing. A uniform and compact metallurgical interface was obtained between the Al and the A356 aluminium alloy, which consisted of the η-Zn, α-Al rich, α + η eutectoid, and primary silicon phases. The microhardness of the interface layer was significantly higher in comparison with those of the Al and A356 matrixes.

Fabrication and Microstructure Evolution of Al/Mg Bimetal Using a Near Net Forming Process

ABSTRACT The Al/Mg bimetal was fabricated by using the lost-foam casting method that is considered a near-net forming process, and the microstructure evolution of the Al/Mg bimetal from different cross-section locations of the bimetal was investigated in the present work. An obvious interface layer generated in the middle of the aluminum and magnesium, which showed a variation for different cross-section locations of the bimetal. The interface layer at the bottom cross-section location had a maximum thickness, wherein a big gap was observed. The thicknesses of the interface layer gradually decreased from the bottom location to the top location. At the middle cross-section location, the interface layer was uniform and compact. In contrast, the non-uniform interface layer was obtained at the top cross-section location, and the partial location had no the interface layer. The interface layers at the bottom and middle locations consisted of three reaction layers including the Al12Mg17 + δ-Mg, the Al12Mg17 + Mg2Si, and the Al3Mg2 + Mg2Si layers. However, the partial location at the top cross-section location only had the Al12Mg17 + δ-Mg layer.

Effect of heat treatment on microstructures and mechanical properties of Al/Fe bimetal

ABSTRACT The Al/Fe bimetallic castings were prepared by the compound casting combined with hot-dip galvanising and aluminising, and the effect of the heat treatment on microstructures and mechanical properties of the Al/Fe bimetallic castings was systematically studied in the present work. The thickness of the reaction layer of the Al/Fe bimetallic castings continuously increased with increasing solution temperature or prolonging solution time. However, the excessive solution temperature and solution time promoted cracks of the reaction layer. Regardless of as-cast or heat treatment, there were respectively the Fe2Al5, Al9Fe4Si3, FeAl3, Al8Fe2Si and Al4.5FeSi phases in the reaction layers. The nano-hardnesses of the reaction layer after heat treatment exhibited an increase compared to that of the as-cast condition.