The flow stress behavior of aluminum alloy 6A10 was studied by the hot compression tests at temperatures from 350°C to 550°C and strain rates from 0.1 s-1 to 10 s-1 with Gleeble-1500 thermo-mechanical simulator.The result demonstrates that the temperatures of specimen differ from initial ones affected by deformation conditions,and that the softening mechanism is dynamic recovery.A new approach was proposed to analyze the flow stress character directly from actual stress,strain,temperature and strain rate data,without performing any previous flow stress correction caused by temperature variation.Comparisons between the experimental and predicted results confirm that the established flow stress model can give reasonable estimation,indicating that the mentioned approach can be used in flow stress model analysis of the materials that undergo only dynamic recovery based on the data obtained under variable deformation temperature.
The evolution of eutectic carbide in as-cast M2 high speed steel was investigated with hot compression test and metallographic examination.Initial rodlike or irregular eutectic carbides were broken into smaller particles during hot deformation by thermomechanical disintegration,while diffusion-controlled phase transformation was not remarkable.Combining with numerical simulation,the relationship between breakdown ratio of carbide network and deformation parameters was obtained.Strain was the most important driving force to shatter eutectic carbides and disperse products.Furthermore,critical strain values were obtained,beyond which carbide network disappeared,and fractured carbides kept a stable profile and they were deformed with matrix coordinately.A higher temperature or lower strain rate resulted in a lower critical strain.
A new processing method,equal channel angular pressing(ECAP)plus cold rolling(CR),was applied to producing ultra-fine grained FeCoV alloy.The microstructures of ultra-fine grained FeCoV alloy after ECAP,ECAP plus CR,and the effect of tempering treatment on the microstructure of FeCoV alloy produced by ECAP plus CR were investigated.The results show that an elongated substructure with a width of about 0.3μm is obtained after four-pass ECAP using Route A.Cold rolling after ECAP cannot change the morphologies of elongated substructure,and it results in higher fraction of high-angle boundaries and higher dislocation density compared with the identical ECAP without rolling.Subsequent tempering for 30 min at 853 K brings about many nano-phases precipitating at subgrain boundaries and insides the grains,and the size of precipitated phase is measured to be about 10 nm.Nano-phases grow up with increasing tempering temperature and equiaxed structure forms at 883 K.
A modified cellular automata (CA) model of dynamic recrystallization (DRX) and a flow stress-based nucleation parameter identification method have been developed.In the method,the modified CA model,which takes the role of deformation degree on nucleation behavior into consideration,is coupled with an adaptive response surface model (ARSM) to search for the optimum nucleation parameter.The DRX behavior of an oxygen free high conductivity (OFHC) copper with different initial grain sizes has been taken as an example to validate the model.Good agreement is found between the simulated and the experimental results,which demonstrates that the new method can effectively improve the simulation accuracy.
