Papers by Author: Jun Xu

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Authors: Meng Ou Tang, Jun Xu, Zhi Feng Zhang, Yue Long Bai
Abstract: Annular electromagnetic stirring (A-EMS) process is an advanced semi-solid metal processing technology. It could avoid the effect of skin effect, increase the shear rate, reduce the temperature gradient and refine microstructures. A three-dimensional computational model sequentially coupling electromagnetic stirring with a macroscopic heat and fluid flow in A357 alloy semisolid slurry preparation by A-EMS has been developed. Comparison between microstructures of A357 alloy produced by EMS and A-EMS has been made. The results show that the annulus gap avoids the part of low magnetic induction intensity and A-EMS avoids the effect of skin effect. The annulus gap prohibits the circular flow and increases the shear flow. The circular flow is more effective than the shear flow on heat dissipation. A lower temperature difference in the stirred melt and subsequent uniformly fine microstructures were obtained as compared with the normal electromagnetic stirring.
Authors: Hai Jun Wang, Jun Xu, Zhi Feng Zhang, Bo Liang, Ming Wei Gao
Abstract: A new coupling stirring technology was proposed and used to prepare direct chill (DC) ingots. Ingots of 7075 alloy were produced by a process of normal direct chill (NDC) casting and coupling-stirring direct chill (CDC) casting, respectively. The effect of the technology on the microstructures, composition segregation and mechanical properties of the ingots was investigated. The results showed that the temperature variation in the CDC casting process was more uniform than that in the NDC casting process. The grain of the CDC ingots was finer and more spherical than the grain of NDC ingots. The grain size at the edge, 1/2 radius, and center position in CDC ingot decrease by 28%, 22%, and 24% comparing with the grain size of the corresponding positions of NDC ingot, respectively. The billets with higher performance and lower macro-segregation were obtained in case of CDC. The flow stresses and the difference in different positions of DC ingots measured at Gleeble-1500D thermo-mechanical simulator decreased obviously when the coupling stirring technology is used in the casting process.
Authors: Jun Xu, Hai Jun Wang, Meng Ou Tang, Zhi Feng Zhang
Abstract: The annular electromagnetic stirring (A-EMS) process, as an advanced melt treatment technology, is increasingly applied in metallurgy industry. DC casting by A-EMS was applied in this study to investigate the solidification behaviour of a modified 7075 alloy. The effects of DC casting without EMS, with normal electromagnetic stirring (N-EMS) and with annular electromagnetic stirring (A-EMS) on microstructure, composition segregation and mechanical properties of continuously cast billets were compared. Research results showed that the billets with higher performance, lower macro-segregation, more uniformly fine solidification structure were obtained in the case of A-EMS.
Authors: Zhi Feng Zhang, Jun Xu, Yue Long Bai, Li Kai Shi
Abstract: An advanced rheo-diecasting technique, based on a modified multi-electromagnetic stirring continuous preparation (MSCP) process was developed for manufacturing near-net shape Al-alloys components with high integrity. The modified MSCP process innovatively combines noncontact electromagnetic stirring and an annular chamber with specially designed profiles to in situ make high quality semisolid slurry, and intensive forced shearing and self-wiping action can be achieved under high shear rate and high intensity of turbulence inside the annular chamber. Three Al-Si alloys with hypoeutectic, eutectic and hypereutectic compositions were tested in this study. The results indicate that, compared with those produced by conventional high-pressure diecasting (HPDC) process, rheo-diecasting samples based on the modified MSCP process have finer and more uniform microstructure.
Authors: Zhi Feng Zhang, Zhi Gang Wang, Bao Li, Jun Xu, Rui Wang
Abstract: An advanced rheo-squeeze casting process, based on the annular electromagnetic stirring (A-EMS) melt treatment technology was developed by GRINM for manufacturing near-net shape Al-alloy components with high integrity. Effects of A-EMS melt treatment process on microstructure and property of squeeze casting Al-Zn-Mg-Cu-Sc alloys were studied. The results revealed that the A-EMS melt treatment process apparently benefited grain refinement and homogeneity, and the hot-cracking of the test alloy for a complicated casting was significantly alleviated, and thus the strength and ductility of the casting were found to be comparable to those of conventionally forged alloys.
Authors: Zhi Hua Gao, Jun Xu, Zhi Feng Zhang, Meng Ou Tang
Abstract: 7075 aluminum alloy melt conditioned by annular electromagnetic stirring(A-EMS) was cast in the TP1 mould, and the effects of pouring temperature, stirring current, stirring frequency and annular gap width on microstructures were analyzed. The A-EMS process exhibits superior grain refinement and remarkable structure homogeneity compared with conventional casting(N-EMS) and conventional electromagnetic stirring casting(EMS). With the increasing of the pouring temperature, the microstructures of the sample conditioned by A-EMS are inclined to become coarse and non-uniform compared with which have the more serious inclination conditioned by N-EMS. With the stirring current or stirring frequency increasing, the rosette-like or dendritic primary α(Al) phase decreases significantly on the sample microstructures, and the non-dendritic primary α(Al) phase is finer and more spherical. Narrow annular gap is advantageous to obtain uniformly fine spherical solidification microstructures.
Authors: Bao Li, Zhi Feng Zhang, Zhi Gang Wang, Jun Xu, Qiang Zhu
Abstract: In the present work, the effects of heat treatment on microstructure and mechanical properties of A390 alloy were investigated. The results show that the as-cast microstructure of A390 alloy mainly consists of primary silicon, α-Al, eutectic silicon and Al2Cu phase. The morphology of primary silicon is irregular polygonal block with sharp edges. Eutectic silicon exhibits a coarse plate-like and acicular morphology and the fishbone like Al2Cu phases are gathered at the grain boundary. During solution treatment, eutectic silicon undergoes fragmentation and spheroidization and T6 heat treatment has a profound effect on the dissolution of Cu and Mg. However, the morphology and size of primary silicon changes little. After the aging process, Al2Cu phases are precipited as lamellar morphology. As a result, the mechanical properties the heat treated A390 alloy increases significantly after T6 treatment.
Authors: Zhi Hua Gao, Jun Xu, Guo Jun Liu, Zhi Feng Zhang, Men Gou Tang, Shao Ming Zhang, Z. Fan
Abstract: Intensive melt shearing achieved using a twin-screw machine was applied to the 7075 aluminum alloy melt to investigate its effects on grain refinement. Alloy melt without and with melt shearing was cast in the standard test procedure mould, and the effects of casting temperature, shearing time and shearing intensity on microstructures were analyzed. The results show that the intensive melt shearing exhibits superior grain refinement and remarkable structure homogeneity. Without shearing, the grain size increases significantly with the increase in pouring temperature, while with intensive melt shearing the grain size is finer at all the pouring temperatures tested with a reduced grain size dependence on the pouring temperature. With the shearing time or shearing intensity increasing, the grain size of the equiaxed primary α (Al) phase decreases on the sample microstructures, and the grain distributions trend to become more fine and non-dendritical.
Authors: Xue Kong, Bi Cheng Yang, Zhi Feng Zhang, Jun Xu
Abstract: The effect of reheating process on the microstructure and mechanical property of A390 aluminum alloy and its evolution mechanism was studied. During reheating process, the microstructure of A390 ingots changed greatly, the microstructure of α-Al particles changed from dendrite to spherical. As the reheating temperature increased primary Si and eutectic Si gradually grew up and spheroidized while the mechanical properties got the maximum value as the ingot reheating to 540°C. The relationship the between reheating power and microstructure was built. Improving reheating power can restrain the growth of grains, but if the reheating power was too high, the microstructure becomes non-uniform. It has been found that reheating of A390 aluminum alloy experiences two processes of grain combination and Ostwald growing.
Authors: Jun Feng Qu, Jun Xu, Qiang Hu, Fu Wen Zhang
Abstract: The solder/substrate reactions, for Sn-1.0Ag-0.5Cu, Sn-1.0Ag-0.5Cu-0.05Ni and Sn-1.0Ag-0.5Cu-0.05Ni-0.02B, were evaluated in what concerns the melting temperature, microhardness, morphology of the solder and chemical composition of the interface layer. The phases formed at the interface between the Cu Substrate and a molten lead-free solder were studied with different stage times. The evaluation of their chemical compositions were performed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS).
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