不同状态纯Mg试样在75-200 ℃, 15-40 MPa条件下的蠕变实验表明: 在等同条件下, 铸态试样的晶粒粗大, 蠕变速率较低; 挤压态试样由于动态再结晶, 晶粒变细, 蠕变速率大幅上升; 退火后由于晶粒长大, 蠕变速率又呈下降趋势. 根据应变速率幂指数公式, 铸态纯Mg试样在较低应力时, 应力指数n处于4.3-4.9的范围, 在较高应力时, n>7; 激活能在76.0-89.4 kJ/mol的范围. 根据应力指数和激活能并结合蠕变过程中的组织分析, 纯Mg的蠕变受位错攀移、晶界滑移以及孪生的共同作用, 其中位错攀移和晶界滑移占主导地位.
The creep behaviors of pure magnesium in different states at the temperatures 75~200℃ under stresses 15~40MPa were studied. The results indicates that the grain size has remarkable effect on the creep behavior. The as-cast magnesium has low creep rate with coarse column crystals. However, the creep rate increases significantly as the grains become fine equiaxed due to dynamic recrystallization after extrusion and deceases when the grains coarsen after anneale-treatments. The stress exponents lie in the range 4.3-4.9 under low stresses,which is consistent with the “Five-Power-Law” suggesting the creep is dislocation climb-controlled. However, the values of over 7 under high stresses indicate power-law breakdown. The apparent activation energies range from 76.0kJ/mol to 89.4kJ/mol. According to the stress exponents and the activation energies as well as the microstructure analysis during creep, the creep are affected by dislocation climb, grain boundary sliding and twinning, among which the former two play dominant role.
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