淬火弹性应变能对7050 铝合金时效亚晶界演变的影响Effect of quenching elastic strain energy on evolution of sub-grain boundaries in 7050 Al alloy during aging

研究7050 铝合金型材在固溶淬火与分级时效各阶段亚晶界的演变，阐明亚晶界形成与晶粒内取向梯度的关系。结果表明：固溶淬火后长轴为200 μm、短轴为80 μm 的纺锤状粗晶组织经过(121 ℃，360 min)+(177 ℃，60 min)双级时效处理后，被分割碎化成20 μm 左右的等轴状细小亚晶组织。电子背散射衍射技术(EBSD)证实碎化由小角度晶界分割造成，且固溶淬火后晶面的弯曲程度经时效后降低了77.8%。透射电镜(TEM)结果表明，时效过程使淬火散乱位错逐步形成位错列和小角度晶界。二级时效时MgZn2 相在亚晶界上析出，促进了Graff 试剂的侵蚀效果，使得在光学显微镜(OM)下可观察到亚晶界。

The evolution of sub-grain boundaries of 7050 Al alloy profiles during solution quenching and interrupted aging treatment was studied,and the relationship between formation of the sub-grain boundaries and the orientation gradient was clarified. The results show that the spindle-shaped grains with 200 μm in length and 80 μm in width after solution quenching break into fine equiaxed sub-grains with average diameter of about 20 μm after duplex aging at (121℃,360 min) and (177 ℃,60 min). EBSD analysis demonstrates that grain refinement results from the segmentation of coarse grains by low angle grain boundaries and the lattice curvature due to solution quenching decreases by 77.8% after aging treatment. The investigation of TEM shows that the scattered dislocations by quenching arrange into dislocation arrays and low angle grain boundaries with aging time. MgZn2 precipitates on the sub-grain boundary,which helps the etchant Graff to visualize the sub-grain boundary using OM in the secondary aging.

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