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The temperature range of high-temperature homogenization was determined by phase diagram calculation and the critical overburning temperature of chromium hypereatectoid steel was measured by DSC. The Comparison of microstructures and element segregation before and after homogenized treatment were investigated for chromium steel ingot by means of optical microscope, scanning electron microscopy and EDS. The results show that the liquation carbides and composition segregation are improved after the chromium steel was treated by high-temperature homogenization. According to the results of EDS analysis and segregation ratio calculation for the samples homogenized at different temperature, the optimum homogenization process for Cr steel is 1210°C for 6h.

LiFePO4/C cathode material with different carbon sources was synthesized by using a two-step carbothermal reduction method. The structure and electrochemical properties of the samples were characterized by XRD, SEM and galvano-static charge-discharge method. The effect of different carbon sources on the structure, morphology and its electrochemical properties of the LiFePO4/C composite materials were investigated. The results showed that the properties of the samples depended on carbon sources, significantly. The sample synthesized by citric acid as carbon source had the best electrochemical performance. The reason of performance difference of the LiFePO4/C composite materials caused by carbon source was discussed.

The effects of Cu addition on precipitation characteristics in 6082 Al-Mg-Si alloy was investigated by means of DSC、TEM and 3DAP. It was found that addition of Cu has distinct effect on the precipitation and dissolution process of precipitates during heating by DSC measurement, the presence of Cu promotes the formation of GP zone or atomic clusters and accelerates the precipitation of β¢¢ . The precipitation sequence in the 6082 alloy with 0.6%Cu addition is as follows:SSSSatomic clusters/GP-zonesβ¢¢ + Q¢ Q¢.

The effect of Si content on structure and wear resistance of cold roll steel with 5%Cr by using vacuum arc melting furnace had been studied in this paper. Results showed that with increasing Si content martensite got coarsening and the number and content of primary carbide increased; The type of primary carbide was M7C3 and Si mainly dissolved into martensite by XRD analysis; The wear resistance was effectively improved while Si content increased. The appropriate Si content in cold roll steel with 5%Cr was 1.5%~2％.

To investigate the effects of thermomechanical treatments (TMT) on the microstructure and properties of Al-Mg-Si alloy, the cold deformation on the ageing precipitation of a solution-treated Al-Mg-Si alloy was studied. The results shows that the time of reaching the peak hardness is shortened with the increasing deformation and an obvious increasing in the peak hardness and tensile strength are occured with higher amount of deformations. The microstructures of peak hardness reveals that the average size of the precipitates becomes smaller in size and greater in number in the alloy with 50% deformations. The study is also carried out to investigate the changes in resistivity of alloys during the ageing time in the alloy with and without 50% deformation. It was found that there are rapidly increasing in resistivity followed by decreasing with the onset of ageing time in both cases. However, the extent of increasing and decreasing in resistivity is much stronger in the alloy with 50% deformation. These results were discussed according to the effects of cold deformation on the dislocations and precipitates in the Al-Mg-Si alloy.

The non-dendritic of A356 aluminum alloy billet was reheated to meet the requirements of the semi-solid microstructure by three different kinds of power, achieving the same final temperature of 863K. Subsequently, under the same conditions of die-casting (thixoforming), the microstructure was observed, surface hardness and tensile properties were measured. Afterwards, quantitative analysis was made for the microstructure of the reheated semi-solid of billet and the thixoforming parts. The results showed that the larger induction reheating power of the billet, the smaller the grain size of its microstructure and the higher surface hardness and the better mechanical properties of its thixoforming sample. Finally, through studying on the relationship between the microstructure of the semi-solid billet of A356 aluminum alloy and the mechanical properties of the thixoforming sample, we primarily achieved the reverse design of microstructure.

The critical overburning temperature of chromium forged steel was experimented and discussed by DSC method and metallographic analysis of heat-treatment samples. Temperature increase during forging process and effects of some alloying elements on overburning temperature were simulated respectively by using Deform-3D and Thermo-calc software. The results of linear regression analysis showed that increased temperature has a prop relationship between volume and rate of forging process. Besides, a monotonic decreasing relationship is found between the content of alloying elements with overburning temperature in the scope of the composition of chromium forged steel. It is found that carbon has the major effect on the overburning temperature.

Simulation method of void defect evolvement during the forging of steel ingot was determined by comparing simulated and experimental results of void closure in the cylinder specimens during forging. Calculation results of long and short void defect evolvement during forging indicated that effective strain required for void closure was induced by the integration of stress. The closure of tetrahedral void is the most difficult with the maximal values of critical reduction on void closure during forging, on the basis of which, theory basis is provided for making forging process.

To enhance the comprehension on the internal rule of microstructure evolvement and quality-controlled relativity, the microstructure during the induction reheating of billets and die casting of parts was systematically investigated. According to general structure observation and aided analysis of some computer simulations, the quantitative relationships between microscopic morphology (including solid fraction and grain shape) and formation state was minutely discussed. The experimental results showed that liquid and solid phase in semi-solid slurry had different filling tendency, fluid velocity of liquid phase in the area of high filling speed was relative quick and easy to flow into far area and corner. Solid particles far from gate possessed fine and round grain. Moreover, the structure configuration of original billets markedly affected forming process; billets with fine and round grain were required for the die-castings of complex shape and thin thickness. In the case of the big change in shape and thickness of die-castings, the design of gating system and the control of plunger speed should be so properly carried out as to avoid unequal distribution of solid and liquid phase in die-casting part as soon as possible.

The precipitation behaviors and microstructures of nano-precipitates in AA6082 Al-Mg-Si alloy with and without Cu additions during heat treatment process were studied using hardness measurements, TEM, mechanical tests and 3DAP. Meanwhile, the softening process of 6082 alloys with Cu and without Cu, isothermally conditioned at 250°C, has also been investigated. It was found that the rate of age hardening, mechanical properties and thermal stability are higher for the Cu-containing alloy. The TEM and 3DAP observations showed that Q’ precipitates were existed after aged at 170°C for 8h in the alloy with Cu addition. Comparing the hardness, mechanical properties and thermal stability curves, it was concluded that the Q’ precipitates play a major role in improving the age hardening kinetics and properties of 6082 alloy with Cu addition.

WC-10Co-0.8VC nanocrystalline powders were sintered by spark plasma sintering (SPS) and hot pressing sintering (HPS), and the microstructure and properties were compared. Results show that, sintered at 1300°C, the sample prepared by SPS for only 3 minutes has higher density than that prepared by HPS for 60 minutes. SEM and SPM observation shows SPS at 1200°C has a more uniform and finer microstructure, and most of the WC grains are smaller than 100nm. It has a relative density of 95.1%, HV30 of 1887, and KIC of 11.5 MPam1/2. If a suitable sintering parameter is chosen, SPS is a promising consolidation technique to prepare nanocrystalline WC-10Co-0.8VC with improved properties.

The morphology of semi-solid alloy is one of the key influence factors on the rheological behavior of slurry during die filling and the mechanical properties of formed parts. However, it is difficult to study such effect due to hard controlling of morphology in semi-solid state. In this paper, a self-developed Searle-type viscometer was used to determine the rheological behavior of A356 aluminum alloy in different morphology, which was refined with the salts mixture of K2TiF6 and KBF4. The results indicated that the flow behavior of refined A356 alloy in the semi-solid state possesses obviously thixotropic behavior under isothermal shearing condition with less time to reach steady state and lower steady apparent viscosity as compared to that of the A356 alloy. During continuous cooling at a constant shearing rate, the apparent viscosity of refined A356 slurry in the same solid fraction decreased with the content of Ti. It is shown from quantitative image analysis that the primary α-Al grain in the refined alloy evolves from dendrites to rosettes or sphericitys, and then tends to be rounder and finer in higher Ti content. The mechanism of the influence of morphology on rheological behavior was also discussed in this paper.

To aid the optimizing design of filling system, computer simulation technique is introduced to predict injection-forming process and to protect defects during trial manufacture of automotive parts by using semi-solid die cast process. By comparing formed appearance of parts in experiments and that in simulations, and observing the relationship between internal defects inspected by X-ray and flow field obtained in simulation, it is indicated that there are quite good agreements between simulation and experiment, right predictions for cast defects resulting from filling process can be made and improving direction is proposed. The realization of numerical visualization for filling process of high speed during semi-solid die cast process will play an important role in optimizing technology plan and process.