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

模式II组件的模式III组件在模式上我加载了7075-T6系列阵列中SCC增强的不同影响，依赖于颗粒结构的不同类型，命名为短反向导向的特定物质的延迟，同时为纵向导向的特定物质的加速。在这些结果的基础上，SCC碎片定位在组合物的加载条件下是确定的。晶体颗粒大小对SCC的高强度合金7475-T6薄片的影响已经使用两种类型的张力特异物进行了调查，并且没有预破解，在3.5%氯化钠溶液中披露。在三种材料A、B和C中，张力特性和分形特性的微小差异被展示在细--、中--和分数--粒度，相应地。光滑标本的SCC断裂时间随着增益大小的增加而增加，命名为物质A<B<C的顺序。对SCC初始化和传播的抵抗力也在增益大小中增强了增加的速度。From the test results together with the elasto-plastic FEM stress analysis， the threshold stress intensity KID2 of SCC initiation is derived to be in agreement with the KID2I D2 condition under that the plastic zone size RID2 =（K-D2I-D2/K-D2ys-D2）K-D12-D1/Crack tip expands to a width of grain diameter， where K-D2ys-D2 is the y？strength。因此，它是支持SCC工艺7457-T6主要由氢实施来控制的，以达到一个关键距离对应的粒度大小，这些结果将为铝合金的开发提供有效的指导方针，使其具有更好的强度、更好的结构组合到SCC。

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.