Size effect on plastic anisotropy in microscale deformation of metal foil
Size effect on plastic anisotropy in microscale deformation of metal foil
复制标题
金属箔微尺度变形中塑性各向异性的尺寸效应
DOI：
10.1016/j.jmatprotec.2019.03.023
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发表时间：
2019-09
影响因子：
6.3
通讯作者：
Min Wan
中科院分区：
文献类型：
--
作者：
Bao Meng;Wenhe Wang;Yiyun Zhang;Min Wan
金属箔广泛应用于微成形工艺中制造高深厚比的微型零件。由于参与金属箔变形的晶粒很少，单个晶粒的力学响应强烈地影响着成形微件的变形行为和质量，导致微成形具有很强的各向异性。为了阐明尺寸对材料各向异性的影响以及尺寸相关的塑性各向异性对金属箔成形性的影响，对厚度为50 ~ 200 μm、晶粒尺寸为10.2 ~ 80.5 μm的SUS304箔进行了拉伸实验和几何缩尺拉深试验。实验结果表明：随着厚度的减小，流变应力、屈服拉伸比（即屈服强度与抗拉强度之比）和延伸率在与轧制方向0°、45°和90°角处的各向异性显著增强，且各向异性对晶粒尺寸有较大的敏感性。此外，在厚度方向晶粒少的金属箔中，奥氏体向马氏体的变形导致了流动行为硬化速率的异常增加。不同方向上的Lankford值、平面各向异性系数和法向各向异性系数随晶粒尺寸的增大和箔厚度的减小而减小。当晶粒尺寸与厚度相当时，由于单个晶粒在较低的oft/ ratio（即厚度与晶粒尺寸之比）下对晶体取向、织构、尺寸和形状的主导响应，箔表现出较强的塑性各向异性。此外，采用了几种宏观屈服准则来表征多尺度拉深过程中的各向异性现象。结果表明，与Hill’48和Von Mises函数相比，Yld2000-2d准则更适合于预测大量晶粒参与微成形的金属箔的各向异性行为。然而，随着t/比的减小，预测精度会下降，当薄膜厚度与晶粒尺寸相同时，Yld2000-2d的使用会出现问题，这与微观塑性变形中晶粒尺寸、薄膜厚度和晶体织构的相互作用密切相关。
Metal foils are extensively used for manufacturing microparts with a high depth-to-thickness ratio by microforming processes. Since there are few grains participating in the deformation of metal foil, the mechanical response of each individual grain intensively affects the deformation behavior and the quality of the formed micropart, which leads to strong anisotropy in microforming. To clarify the size effect on material anisotropy and the impact of scale-dependent plastic anisotropy on the formability of metal foil, a series of tensile experiments and geometrically scaled-down deep-drawing tests of SUS304 foil with different thicknesses of 50–200 μm and grain sizes of 10.2–80.5 μm were performed. The experimental results indicate that the anisotropy of flow stress, yield tensile ratio (i.e., ratio of the yield strength to the tensile strength) and elongation at angles of 0°, 45° and 90° to the rolling direction is prominently enhanced with decreasing thickness and that the anisotropy generally shows a substantial sensitivity to grain size. In addition, the abnormally increased hardening rate of flow behavior for metal foil with few grains in thickness direction arises from the deformation-induced transformation from austenite to martensite. The Lankford values in different orientations, the planar anisotropy and normal anisotropy coefficients decrease with increasing grain size and decreasing foil thickness. The foil manifests strong plastic anisotropy when the grain size is comparable to the foil thickness due to the dominant response of individual grains in terms of crystal orientation, texture, size and shape at a low value oft/dratio (i.e., the ratio of the thickness to the grain size). Furthermore, several macroscale yield criteria are adopted to characterize the anisotropic phenomenon in the multi-scaled deep drawing process. The results suggest that the Yld2000-2d criterion is more suitable than Hill’48 and Von Mises functions to predict the anisotropic behavior of metal foil with a large number of grains involved in microforming. However, the prediction precision is worsened with decreasingt/dratio, and the use of Yld2000-2d becomes problematic when the foil thickness is of the same magnitude as grain size, which is closely linked to the interactive effects of grain size, foil thickness and crystallographic texture in microscale plastic deformation.
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影响因子：
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影响因子：
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