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Study on Development if High Strength-Toughness- and Environmental Strength-Aluminum Alloys with Fine Grain Structure

高强韧环保强细晶结构铝合金的开发研究

基本信息

批准号：
09650762
负责人：
OSAKI Shuhei
金额：
$ 2.56万
依托单位：
Yamaguchi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09650762/
关键词：
Aluminum Alloy Stress Corrosion Cracking Fine Grain Structure Grain Boundary Crack Tip Plastic Zone Hydrogen Embrittlement Loading Mode Precipitation 水素脆化

项目摘要

The superposition of mode II of mode III component onto mode I loading has a different effect on SCC intiation in 7075-T6 series alloys, depending on the anisotropy of grain structure, namely causing a delay for the short-transverse oriented specimen, while an acceleration for the longituditinal oriented specimen. On the basis of these results, the SCC fracture loci under the combines loading conditions is determined.The effect of crystal grain size on the SCC of a high-strength alloy 7475-T6 sheet has been investigated using two types of tensile specimens with and without pre-crack, exposed in 3.5% sodium chloride solution. Little differences in the tensile property and fracture toughness are exhibited in the three materials A, B and C, having a fine-, medium- and coarse-grain size, respectively. The SCC rupture time of the smooth specimen is prolonged with the increase in gain size, namely in the order of material A<B<C. The resistance to SCC initiation and propagation of the pre-cracked specimen is also enhanced with the increase in gain size. From the test results together with the elasto-plastic FEM stress analysis, the threshold stress intensity KィイD2ISCCィエD2 of SCC initiation is derived to be in agreement with the KィイD2IィエD2 condition under that the plastic zone size RィイD2pィエD2=(KィイD2IィエD2/ σィイD2ysィエD2)ィイD12ィエD1/π in front of crack tip expands to a width of grain diameter, where σィイD2ysィエD2 is the yield strength. Thus it is supported that the SCC process of the alloy 7457-T6 is principally controlled by hydrogen embrittlement achieved over a critical distance corresponding to one size of grain.These results will give effective guidelines for the development of aluminum alloys with a better combination among strength, fracture toughness and resistance to SCC.

在7075-T6系列合金中，III型分量的II型叠加到I型加载对SCC的激发有不同的影响，这取决于晶粒组织的各向异性，即对短横向取向试样产生延迟，而对纵向取向试样产生加速。在此基础上，确定了复合加载条件下SCC的断裂位置。采用3.5%氯化钠溶液中存在和不存在预裂的两种拉伸试样，研究了晶粒尺寸对高强度合金7475-T6板材SCC的影响。A、B、C三种材料的拉伸性能和断裂韧性差异不大，分别为细晶粒、中晶粒和粗晶粒。光滑试样的SCC破裂时间随增益尺寸的增加而延长，即材料A<B<C的顺序。随着增益尺寸的增大，预裂试样的抗SCC萌生和扩展能力增强。从测试结果与弹塑性有限元应力分析,门槛应力强度KィイD2ISCCィエD2的鳞状细胞癌起始派生与K一致ィイD2IィエD2条件下塑性区大小RィイD2pィエD2 = (KィイD2IィエD2 /σィイD2ysィエD2)ィイD12ィエD1 /π面前的裂纹尖端扩展宽度的颗粒直径,在σィイD2ysィエD2是屈服强度。由此可见，合金7457-T6的自晶化过程主要受一种晶粒尺寸对应的临界距离上的氢脆控制。这些结果将为开发强度、断裂韧性和抗SCC性能更好结合的铝合金提供有效的指导。