对AZ31镁合金轧制态板材分别在473~673 K温度范围退火1 h以获得不同初始显微组织.通过金相显微镜、背散射电子衍射分析(EBSD)和力学试验机,研究晶粒尺寸和取向分布对合金板材室温单向静拉伸过程塑性变形和断裂机制的影响.结果表明,晶界取向角呈连续分布有利于晶粒协调塑性变形.随着晶粒尺寸的降低,晶界对室温塑性变形的贡献增大,晶界与位错滑移和孪生的交互作用增强.对于取向角均呈连续分布的473 K和573 K退火态板材,平均晶粒尺寸分别为3.6μm和9.5μm,塑性变形主导机制由晶界滑动和位错滑移转变为晶界滑动、位错滑移和孪生,断裂机制由微孔聚集型转变为微孔聚集型和解理型混合型断裂方式.673 K退火态板材的平均晶粒尺寸达22.9μm,塑性变形主导机制为位错滑移和孪生.此时,由于晶界取向角呈离散分布,晶粒协调塑性变形能力差,断裂机制转变为解理断裂.%Different initial grain sizes and misorientation of AZ31 alloy sheets were obtained by different annealing temperatures of 473-673 K for 1 h, respectively. The mechanisms of plastic deformation and fracture were investigated by optical microscope, EBSD and tensile test with strain rate of 1×10-3 s-1 at room temperature. The results show that the continuous distribution of grain boundary misorientation angle(GBMA) inclines to improve the ability of grain coordination plastic deformation. With decreasing grain sizes, the contribution of grain boundary on plastic deformation at room temperature increases for improving the interaction between grain boundary sliding(GBS) and dislocation slipping(DS) as well as twinning. As for the alloy sheets annealed at 473 K and 573 K, which present the mean grain sizes of about 3.6 μm and 9.5 μm with continuous distribution of GBMA in both, the mechanism of plastic deformation transforms from the domination of interaction of GBS and DS to that of GBS, DS and twinning. And the fracture mechanism transforms from the micropore aggregation fracture to the mixture fracture, combining with micropore aggregation and cleavage. While as for the sheet annealed at 673 K, characterized by the average grain size of about 22.9 μm and disperse distribution of GBMA, the mechanism of plastic deformation is dominated by DS and twinning, and the fracture mechanism changes into cleavage fracture for the poor ability of grain coordination plastic deformation.
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