铝-银合金在疲劳过程中所表现的一些特点

本工作进行了淬火Al-7.27％Ag合金的扭转疲劳试验,测定了各种扭应变下的△E-N曲线,并且观察了经过各种循环数以后试样的表面金相变化。实验结果指出,当扭应变较小时,△E随着循环数N的增加而逐渐下降,△E-N曲线的变化类似Al-Cu和Al-Mg合金在较低扭应变下的情况。但当扭应变较大时,△E开始略有下降,随后上升到某一较高值后再下降,直至试样断裂。△E-N曲线的形状与Al-Cu和Al-Mg合金完全不同。试样表面的金相变化分为两个明显不同的阶段。在疲劳的起始阶段,滑移痕迹细而均匀,但经过一定循环数后,少数滑移痕迹变得集中而深化。随着循环数的增加,新的滑移带在原有滑移带之间不断地出现,没有纯Al和Al-Mg合金中滑移带变宽的情况。还看到了裂纹沿晶界的形成和发展。根据溶质银原子与位错的电交互作用和位错切割银原子簇的观点,对所得到的结果进行了讨论。 关键词：

PECULIARITIES EXHIBITED BY ALUMINIUM-SILVER ALLOY IN THE PROCESS OF FATIGUE LOADING

Torsional fatigue experiments were performed with Al-7.27% Ag alloy in the quenched state. The △E-N curves were determined under various torsion strains and metallographie observations were made on the specimen surface after various numbers of stress cycles.Experimental results showed that, when the torsion strain is small, △E was found to decrease with the increase of stress cycle N. The change of the △E-N curves is similar to those previously reported for Al-Cu and Al-Mg alloys under lower torsion strains. However, when the torsion strain is large, AE decreases slightly at the beginning, increases subsequently to some higher value, and drops again until the specimen is fractured. The shape of the △E-N curves is very different from those of Al-Cu and Al-Mg alloys at same strains. The metallographie change of the specimen surface during cyclic deformation was found to be divided into two distinct stages. In the initial period of fatigue loading, fine straight slip lines are homogeneously distributed within certain grains. However, some of them suddenly become highly concentrated and prominent after a certain number of cycles. With increasing fatigue cycles, newly generated localized slip bands occur successively between the existing ones. This observation is markedly different from that observed on pure aluminiun and the quenched Al-Mg alloys, where only the existing slip regions appeared to become broader with the increase of cyclic straning. In addition, fatigue cracks were frequently observed to initiate and propagate along grain boundaries.The results obtained was discussed in terms of the electrical interaction of silver atoms with dislocation and the cutting effect of the to-and-fro moving dislocations though spherical clusters of silver solute atoms.