Dislocation Density and Grain Size Evolution in the Machining of Al6061-T6 Alloys
Dislocation Density and Grain Size Evolution in the Machining of Al6061-T6 Alloys
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DOI：
10.1115/1.4027675
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发表时间：
2014-08
影响因子：
4
通讯作者：
L. Ding;Xueping Zhang;C. Liu
中科院分区：
文献类型：
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作者：
L. Ding;Xueping Zhang;C. Liu
本研究的重点是解决高速加工产生的严重塑性变形（SPD）行为和加工参数对加工表面微观结构变化的影响。建立了高速正交加工Al6061-T6合金的有限元模型。通过从该模型中提取应变、应变率、应力和温度，将基于位错密度的模型作为用户自定义的子程序纳入其中，以预测加工表面的位错密度和晶粒尺寸。预测结果表明，位错密度随加工深度的增加而减小，而晶粒尺寸则相反。切削速度越快，塑性变形层越薄。加工表面位错密度随切削速度的增加而减小，而晶粒尺寸随切削速度的增加而增大。位错密度随进给量先减小后增大。在加工表面产生最大SPD层存在一个临界进给速率。刀具前倾角对塑性变形层深度影响较大。因此，它影响了位错密度和晶粒尺寸的分布。较大的负前角会导致加工表面位错密度增大。在切削参数范围内，预测的切屑厚度、切削力、位错密度分布和晶粒尺寸在切屑形貌、切削力、显微组织以及切屑和加工表面的显微硬度等方面与实验结果吻合较好。
This study focuses on addressing the severe plastic deformation (SPD) behavior and the effects of machining parameters on microstructure alternations in machined surface created from high-speed machining. A finite element (FE) model is proposed to predict the orthogonal machining of Al6061-T6 alloys at high speeds. By extracting strains, strain rates, stresses, and temperatures from this model, a dislocation density-based model is incorporated into it as a user-defined subroutine to predict dislocation densities and grain sizes in machined surface. The predicted results show that dislocation densities decrease with the depths below the machined surface, but grain sizes present an opposite tendency. Higher cutting speeds are associated with thinner plastic deformation layers. Dislocation densities decrease with cutting speeds, but grain sizes increase with cutting speeds in machined surface. Dislocation densities decrease initially and then increase with feed rates. There exists a critical feed rate to generate the maximum SPD layer in machined surface. Tool rake angle has a great impact on the depth of plastic deformation layer. Thus, it affects the distributions of dislocation densities and grain sizes. A large negative rake angle can induce an increased dislocation density in machined surface. The predicted chip thicknesses, cutting forces, distributions of dislocation densities, and grain sizes within the range of machining parameters have good agreement with experiments in terms of chip morphology, cutting forces, microstructure, and microhardness in chip and machined surface.