Papers by Author: Jian Min Zeng

Abstract: Al-5Zn-0.03In series alloys have been widely studied and used as sacrificial anode materials. Adding rare-earth (RE) element to Al-5Zn-0.03In sacrificial anode is the important way to improve its microstructure and properties. This paper focused on the effect of Er addition on the microstructure and properties of the Al-5Zn-0.03In-xEr alloy. Thermal analysis showed that the presence of Er in the series alloys reduced the solidification ranges and made their liquidus and solidus move to lower temperature. The microstructural analysis and hardness testing reveal that Er existed in the form of precipitation, refined the dendrites of the series alloys and improved the hardness of the series alloys. Investigation of the potentiodynamic polarization and the electrochemical impedance measurements were performed in 3.5 wt. % NaCl solution. The potentiodynamic polarization results indicated that the corrosion potential increased and the corrosion current density reduced with the increase of the Er addition. The Al-5Zn-0.03In alloy shows higher corrosion resistance with the increase of Er content. The EIS electrochemical impedance results showed that Al-5Zn-0.03In anode presented relatively uniform dissolution due to the refined microstructure by the addition of Er.

Abstract: Linear segregation of high strength aluminum alloy ZL205A castings were studied by X-ray Nondestructive testing, scanning electron microscope and energy dispersive spectrometer. It is found that the linear segregation occurs at the large wall thickness of the casting and/or at the place where the wall thickness is in transition. Segregation element is mainly Cu, which exists as compound θ (Al₂Cu) phase. The formation of linear segregation is related to the flow of Cu-rich melt in the late solidification period, while the occurrence of thermal cracks promotes the formation of linear segregation. The formation of linear segregation of the casting can be effectively prevented by eliminating hot spots of the casting, refining crystal grains and increasing solidification speed of the casting.

Abstract: A solidification model of coarsening coefficient for the criterion of secondary dendrite arm spacing has been established in this paper. When the model is applied to aluminum cast alloy, it is found that the model is in good agreement with the experiment results. Experiments and analysis show that addition of some chemical elements is conducive to the refinement of the secondary dendrite arm spacing under the same solidification condition. Different chemical elements have different refining effects, and Zr and Ti have better refining effect on A357 aluminum cast alloy than Cu.

Abstract: A new sacrificial Al-5Zn-0.03In-Er alloy was developed with improved microstructure consisting of Er rich phase and refined α-Al. This paper focused on the influence of Er as alloying element on the microstructure and hardness of Al-5Zn-0.03In alloy. With the increase of Er content, the α-Al was refined and the hardness was improved, at the same time a amount of Er rich phases and particles also appeared. The segregation of Er in the front of the solidification interface results in the refining of α-Al. The higher hardness of the Er containing alloy make it possilbe to apply the alloy under a complicated enviorment where the mechanical property is requred. It is concluded that 4 wt% Er is optimum to obtain the refined microstructure and proper hardness.

Abstract: With development in electronic technology, more and more electronic elements have been integrated into one chip, which has resulted in the cooling problem of the chips. In this case, heat dissipation has become the main factor that affecting the design reliability and package cost. Therefore, good heat dissipation designs are urgently need to solve the problem. An important issue resulted from simulation of heat dissipation is the determination of boundary condition between the heat sink and the CPU. The concept of thermal contact resistance was introduced to simulation of heat dissipation of CPU heat sinks in this paper. The temperature distribution of CPU heat sinks was calculated Based on ANSYS software. The result of calculation can help to understand the heat transfer characteristics of CPU heat sinks, and also offer a reference for the design and improvement of the electronic equipment.

Abstract: According to the characteristics that purple red of nixing pottery contains an amount of calcite; different samples were fired with different content of calcite in the mud and varying temperature under oxidizing conditions. The phase composition and microstructure were analyzed. The results show that number and size of pores in the sintered samples increased and pore morphology changed from irregular closed hole to round closed then converted to irregular inter-connected one along with the increase of calcite content. As calcite content in the mud increases the viscosity of liquid phase decreases while the crystalline phase gradually increased as sintering, thus wollastonite phase transformed into eutectic phase of aluminum scapolite and wollastonite, and quartz content gradually reduced. Higher sintering temperatures and content of calcite were helpful to the reduction in viscosity, as calcite content increased gradually, the amount of liquid phase increased at first then decreased.

Abstract: A356 is a heat treatable cast alloy which has been widely applied in aviation and automobile industries. In this paper a Sb modified A356 alloy cast with permanent mold has been investigated in order to improve its mechanical properties by changing the needle morphology of the eutectic silicon. The results show that a small amount of Sb addition can contribute refined eutectic silicon morphology and enhance the mechanical properties, especially elongation of the A356 cast alloy poured in permanent molds. The optimal addition of Sb is 0.2 wt.%.

Abstract: 357-T6 is an alloy that has been widely used due to excellent casting properties and mechanical performances. The aluminum wheels can be cast with both permanent and low pressure die castings. In this study, the mechanical properties of 357-T6 were compared between the gravity permanent casting (GPC) and low pressure die casting (LPDC). The specimens were cast through permanent and LPDC processes, respectively and were heat treated under T6, with different aging temperatures 155°C, 165°C, 175°C and 185°C after the solution treatment of 545°C for 9 hours. The ultimate tensile strength and elongation were tested for both processes. The results show that both tensile and elongation of low pressure die casting specimens are higher remarkably than those in gravity permanent casting. The optimized aging parameter is heating at 175°C for 4.5 hours after solution treatment.

Abstract: A new Al₂O₃ particle reinforced Al matrix composite was fabricated through in-situ chemical reaction between Al and glass powder. The microstructures and element distributions of the composite were observed and analyzed through OM, SEM and EDS, respectively. The results show the reinforced Al₂O₃ particle synthesized by in-situ chemical reaction are aggregated on the grain boundary. The grains can be refined with the increasing of powder. Eutectic silicone with granulous shape was found in the microstructure, which attributes to the modification of Na and Ca to eutectic silicone.

Abstract: Investment casting is one of main precision casting processes to realize near net shape castings. For the castings with thin-walled cross section or complicated shape, it is easy to generate casting stress such as thermal stress, mechanical stress and phase transformation stress, resulting in casting deformation due to the uneven cooling and hindered contraction. Once three-dimensional deformation is formed, it is very hard to correct. In this paper the finite element method (FEM) was used to analyze the stress and deformation of thin-walled lost wax casting. The results show that the temperature and stress distributions are uneven in the casting and the tendency to deform is higher even with insulating shell mold. And based on the results, the technical measures of adding supporting ribs are adopted to restrain deformation. The practice of volume production indicates that no casting was rejected due to deformation defects.