Cu含量对Al-5Zn-2.6Mg-xCu合金组织和性能的影响

Effect of Cu Content on Microstructures and Properties of Al-5Zn-2.6Mg-xCu Alloy

摘要: 本文以添加0.24 wt.%~0.91 wt.% Cu含量的Al-5Zn-2.6Mg合金为研究对象，通过透射电镜(TEM)表征了Cu含量对晶内η'相的影响，通过扫描电镜(SEM)表征了杂质粗大第二相的尺寸与分布；105℃，120℃和135℃下的时效硬化曲线结果表明，随着Cu含量的增加，峰值时效时间提前。借助Arrhenius方程计算了三种时效温度下的析出速率和激活能，计算结果表明，随着Cu含量从0.24%增加到0.91%，时效反应速率k加快，且析出激活能Ea从25.7 kJ降低到15.0 kJ。通过室温拉伸、扫描电镜断口分析研究了Cu含量对强度和韧性的影响规律。随着Cu含量的增加，析出相分布密度明显增加。因此，120℃下峰值时效的抗拉强度提高10.2%；但是，粗大杂质第二相横向尺寸和数目也增多，促使变形过程中裂纹的萌生及在晶界扩展的倾向性增强，导致韧窝数量减少，断口形貌从塑性穿晶断裂转变至脆性沿晶断裂，合金延伸率下降3.8%。

Abstract: In this paper, Al-5Zn-2.6Mg alloy with 0.24 wt.% - 0.91 wt.% Cu content was studied. The effect of Cu content on the η' phase in grain was characterized by transmission electron microscopy (TEM). The size and distribution of the impurity coarse second phase were characterized by scanning electron microscopy (SEM). The age hardening curves at 105˚C, 120˚C and 135˚C showed that with the increase of Cu content, the peak aging time was advanced. The precipitation rate and activation energy at three aging temperatures were calculated by Arrhenius equation. The results showed that the aging reaction rate k increases with the increase of Cu content from 0.24% to 0.91%, and the precipitation activation energy Ea decreases from 25.7 kJ to 15.0 kJ. The influence of Cu content on the strength and toughness was studied by room temperature tensile test and fracture analysis by SEM. With the increase of Cu content, the distribution density of precipitates increases obviously. Therefore, the tensile strength of peak aging at 120˚C is increased by 10.2%. However, the size and number of the coarse impurity second phase are also increased, which increases the tendency of crack initiation and propagation at the grain boundary, resulting in the decrease of dimple areas. The fracture morphology transforms from the plastic trans-granular fracture to brittle intergranular fracture, and the elongation of the alloy decreases by 3.8%.