Papers by Author: Li Jia Chen

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Authors: Li Jia Chen, Jia Li, Feng Li, Xin Wang
Abstract: Cyclic deformation for two magnesium alloys AZ91 and AM50 with different processing status has been performed under total strain amplitude control mode and at room temperature. A serrated flow can be observed in both tensile and compressive directions of the stress-strain hysteresis loop for as-extruded AZ91 and AM50 magnesium alloys. It means that the so-called dynamic strain aging occurs during cyclic deformation. In addition, the dynamic strain aging phenomenon can also be observed in two extruded magnesium alloys subjected to aging treatment as well as the AZ91 alloy subjected to solution treatment. However, the dynamic strain aging seems not to take place in the extruded AM50 alloy subjected to solution treatment because there exists no significant serrated flow behavior in either compressive or tensile direction of the stress-strain hysteresis loop. It is suggested that the occurrence of the dynamic strain aging is associated with collective behavior of many mobile dislocations as well as interactions between solute atoms and dislocations.
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Authors: He Ma, Li Jia Chen, Lian Quan Guo, Li Leng, Lin Lin
Abstract: In this study, equilibrium lattice parameters, heat of formation and cohesive energy of four kinds of typical phases with different structure intermetallic compound in Al-Cu-Mg alloy were investigated by first-principles calculations based on density functional theory via CASTEP software. The calculation results are analyzed and show that ternary strengthening phase Al2CuMg generated first when Mg content is higher, while binary strengthening phase Al2Cu or Al3Cu2 first generated and more stable when Mg content is low in Al-Cu-Mg alloy which indicates that element Cu and Al alloying capacity significantly higher than that of Mg and Al element.
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Authors: Shu Ying Yin, Li Jia Chen, Xin Wang
Abstract: In order to identify the influence of solid solution, aging and solid solution plus aging treatments on the low-cycle fatigue behavior of the extruded AZ61 magnesium alloy, the low-cycle fatigue tests were performed at room temperature for the extruded AZ61 magnesium alloy with different treating states. The results indicate that the cyclic stress response behavior of the extruded AZ61 magnesium alloy exhibits both cyclic strain hardening and stability. The solid solution, aging and solid solution plus aging treatments tend to decrease the cyclic deformation resistance of the extruded AZ61 alloy in most conditions. The solid solution treatment can enhance the fatigue lives of the extruded AZ61 alloy at medium total strain amplitudes. In addition, the aging treatment can prolong the low-cycle fatigue lives of the AZ61 alloy at most total strain amplitudes, while the case for the solid solution plus aging treatment is just contrary. For the extruded AZ61 alloy with different treating states, a linear relationship between cyclic stress amplitude and plastic strain amplitude is noted.
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Authors: Feng Li, Sheng Guo, Xin Che, Li Jia Chen
Abstract: Equal channel angular pressing (ECAP) was conducted using the die with a 90° angled channel under routes A, BC and C for hot extruded AZ91 magnesium alloy. Tensile tests were carried out at 300 °C and initial strain rates ranging from 2×10−4 to 5×10−3 s−1. The experimental results show that different routes have obviously effect on elongation to failure. It is found that the highest elongation to failure is 410 % at a strain rate of 2×10−4 s−1 for the ECAPed AZ91 alloy with route BC. At the same strain rate, route BC can bring the greater superplasticitic deformation compared with routes A and C. Moreover, the strain rate sensitivity coefficient m values of about 0.3 to 0.5 are attained for the ECAPed AZ91 alloys with different routes. For the ECAPed AZ91 alloys, the main superplastic deformation mechanism is the grain boundary sliding, while the main accommodation mechanism is the dislocation creep mechanism controlled by the grain boundary diffusion.
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