Papers by Author: Jun Xu

Abstract: Semi-solid thixoforming process was applied to produce track shoe of 15%SiCp/2A14 composites. The thixoforming process optimization was simulated by using Deform 3D software. The effects of forging pressure, slug size and reheating temperature on formability of track shoe were investigated. The results showed that a track shoe with better integrity was prepared by optimizing the process, and its microstructure and mechanical properties could meet requirements.

Abstract: The apparent viscosities of the semi-solid SiCp/A357 composites with 0vol.%, 10vol.% and 20vol.% SiC particles manufactured by stir casting were investigated using a Couette type viscometer, and the composite fluidity was examined with a test casting. The results showed that, the viscosities of the semi-solid SiCp/A357 composites decreased with an increase in shear rate, but increased with the increasing of solid fraction, and apparent viscosity of 10vol.% SiCp/A357 composite was the lower than that of 20vol.% SiCp/A357 composite at the same solid fraction; and the composite fluidity results were in a good agreement with the viscosity ones.

Abstract: An appropriative alloy for semisolid forming has been designed by mean of optimizing chemical compositions of main elements and microalloying. In this study, thixo-forging process was developed for the appropriative alloy to produce scroll of automobile AC compressor. The results showed that the billet microstructure of the appropriative alloy imposed by A-EMS was fine and uniform, which benefited for effective control in the reheating process, and scrolls with integrity were obtained by optimizing process parameters.

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.

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.

Abstract: The effects of annulus gap width, stirring power and stirring frequency on the microstructure of the semi-solid A356 aluminum alloy slurry have been investigated by the annulus electromagnetic stirring (AEMS) technology The results show that narrow annulus gap , strong stirring power and high stirring frequency are advantageous to obtain the small spherical primarymicrostructure, the smaller the annulus gap width is, the bigger the stirring power is, and the higher the stirring frequency is, the more uniform, the smaller and the more spherical the microstructure is. So the high stirring frequency, narrow annulus gap, strong stirring power are beneficial to obtain the fine and spherical semisolid microstructure in AEMS. Also the results indicate that the primary particles are globular, small and distribute homogeneously in the AEMS.

Abstract: The effect of trace Sc and Zr on grain refinement of Al-7.2Zn-2.2Mg-1.8Cu as-cast ingot was studied by using optical microscopy and scanning electron microscopy with EDS. The results show that addition of only 0.20% Zr or 0. 20% Sc to Al-7.2Zn-2.2Mg-1.8Cu alloy can refine grains to a certain degree, and the addition of 0.10% Sc+0.20%Zr leads to stronger grain refinement, the average grain size is only 10-15μm. Al₃Sc/Al₃Zr composite particles in the melt work as the nucleation of heterogeneous nucleation during solidification.

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).

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.

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.