Inhomogeneity of Microstructure and Properties of 7085-T651 Aluminum Alloy Extra-thick Plate
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摘要: 采用拉伸实验、剥落腐蚀实验、显微组织、化学成分、扫描电镜以及透射电镜和差示扫描量热法分析等手段，研究7085-T651铝合金特厚板组织性能的不均匀性。结果表明：110 mm厚7085-T651特厚板不同厚度层显微组织、力学性能和剥落腐蚀性能存在明显的不均匀性；1/4厚度层抗拉强度最低，为540 MPa，抗剥落腐蚀性能最差，腐蚀等级为EB级；心层抗拉强度最高，为580 MPa；表层抗剥落腐蚀性能最好，腐蚀等级为EA级；1/4层再结晶分数最多，约为47.7%，尺寸较大，约为105 μm，晶界及晶内均有平衡相析出，时效析出相尺寸较小，因而力学性能及抗剥落腐蚀性能均最差；中心层再结晶分数最少，约为14.8%，存在大量亚晶，残余的Al7Cu2Fe相最多，约为1.43%，晶界平衡相尺寸、时效析出相尺寸及PFZ宽度均较大，因而力学性能较好而抗剥落腐蚀性能较差。Abstract: Inhomogeneity of microstructure and properties of 7085-T651 aluminum alloy extra-thick plate were investigated by tensile properties, exfoliation corrosion, optical microscopy(OM), composition analysis, scanning electron microscopy(SEM),differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The results show that the microstructure, tensile property and exfoliation corrosion in different layers of 7085-T651 aluminum alloy of 110 mm thick are inhomogeneous. For the 1/4 thickness layer, the tensile strength is the minimum, 540 MPa, and the resistance to exfoliation corrosion of this layer is the worst, with exfoliation corrosion classification of EB. For the core layer, the tensile strength is the maximum, 580 MPa. The resistance to exfoliation corrosion of the surface layer is the best, with exfoliation corrosion classification of EA. For the 1/4 thickness layer, it has the largest recrystallized fraction up to about 47.7% and the grain size is about 105 μm; there are equilibrium phase particles precipitated on grain boundaries or within grains; the size of aging precipitates is small; and thus both mechanical properties and resistance to exfoliation corrosion are the worst. For the core layer, it has the smallest recrystallized fraction of about 14.8% and there are a large amount of sub-grains; the fraction of residual phase Al7Cu2Fe almost reaches up to about 1.43%; the size of the equilibrium phase on grain boundaries, the size of aging precipitates and the width of PFZ are large, and therefore good mechanical properties and bad resistance to exfoliation corrosion are obtained.
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Key words:
- 7085 aluminum alloy /
- extra-thick plate /
- inhomogeneity /
- precipitate free zone
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图 1 7085-T651特厚板不同层拉伸性能
Figure 1. Tensile properties at different layers of 7085-T651 aluminum alloy extra-thick plate
图 2 7085-T651特厚板不同层断口SEM照片
Figure 2. SEM images at different layers of 7085-T651 aluminum alloy extra-thick plate (a)，(b) surface；(c)，(d)1/4 layer ；(e)，(f) center
图 3 7085-T651特厚板表层(1) ，1/4层(2) 和中心层(3) 剥落腐蚀形貌 (a) 12h；(b) 48 h
Figure 3. Corrosion morphologies of 7085-T651 aluminum alloy extra-thick plate at surface(1) ，1/4 layer(2) and center(3) (a) 12h；(b) 48 h
图 4 7085-T651特厚板不同层的金相照片 (a)表面;(b)1/4层；(c)，(d)中心
Figure 4. Metallographs at different layers of 7085-T651 aluminum alloy extra-thick plate (a) surface；(b) 1/4 layer；(c)，(d) center
图 5 7085-T651特厚板不同层SEM照片 (a)表面；(b)1/4层；(c),(d)中心
Figure 5. SEM images at different layers of 7085-T651 aluminum alloy extra-thick plate (a)surface；(b)1/4 layer；(c)，(d)center
图 6 7085-T651特厚板不同层TEM照片 (a)，(b)表层；(c),(d)1/4层;(e),(f)中心层
Figure 6. TEM images at different layers of 7085-T651 aluminum alloy extra-thick plate (a)，(b) surface；(c)，(d) 1/4 layer；(e)，(f) center
图 7 7085-T651特厚板不同层的 DSC曲线及处理结果
Figure 7. DSC curves(a) and results(b) at different layers of 7085-T651 aluminum alloy extra-thick plate
表 1 不同厚度层的化学成分(质量分数/%)
Table 1. Chemical composition of different thickness layers (mass fraction/%)
Layer Zn Mg Cu Fe Si Zr Ti Al Surface 7.06 1.52 1.71 0.0326 0.0076 0.111 0.0346 Bal. 1/4 layer 7.08 1.53 1.74 0.0335 0.0080 0.109 0.0336 Bal. Center 7.12 1.56 1.77 0.0319 0.0077 0.111 0.0370 Bal. 
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