时效、断续载荷和再溶处理对于铝铜合金的疲劳过程的影响

【摘　要】本文研究了各种处理对于含铜1％、2％和4％的铝合金在疲劳载荷下ΔE和T_m的变化的影响,并进行了相应的金相观测。用Al-1％Cu合金所进行的试验指出,当外加扭应变较大时,ΔE和T_m曲线的形状类似于高纯铝或工业纯铝;当扭应变较小时,或在室温进行预先时效后,曲线的形状类似于Al-4％Cu合金。这些结果都可以根据溶质原子对于位错的交互作用的看法得到解释。对于Al-1％Cu和Al-2％Cu合金进行了断续的疲劳载荷试验,结果证明了ΔE在疲劳后期的上升是由于试样里出现了集中的粗滑移区,而不是由于疲劳载荷引起了过时效从而使试样发生软化的结果。用Al-4％Cu合金进行了疲劳和再溶处理的试验,根据ΔE和T_m曲线的表现情况来看,认为如在ΔE的后期上升后立即对试样进行再溶处理,即可以使试样回复到原来的状态,但当ΔE上升过了一个时期以后,由于试样中已有裂缝出现,对试样进行再溶处理,反足以加速试样的断裂。根据实验结果,可以总结出两个具有实际意义的推论:(1)由于粗滑移带的出现是形成疲劳裂缝的先声,所以有可能通过测量ΔE的方法来查知初发裂缝的形成;(2)通过加入合金元素和进行热处理的方法,可以推迟粗滑移带的出现,从而提高铝合金试样的疲劳寿命。

EFFECT OF AGING, INTERMITTENT LOADING AND RE-SOLUTION TREATMENT UPON THE FATIGUE BEHAVIOR OF ALUMINUM-COPPER ALLOYS

A study was made on the effect of various treatments upon the energy loss △E and the maximum torque T_m in aluminum-copper alloys containing 1%, 2% and 4% copper under fatigue loading. Metallographic observations were made correspondingly.Experiments made with Al-1% Cu alloy showed that when the applied torsional strain is large, the shapes of the △E and T_m curves are similar to that of high-purity aluminum and commercial aluminum. However, when the torsional strain is small, or when the specimen was aged at room temperature before the fatigue experiment, the shapes of the △E and T_m curves are similar to those of Al-4% Cu alloy. These results can all be interpreted in terms of the interaction between solute atoms and dislocations.Experiments on intermittent loading were made on Al-1% Cu and Al-2% Cu alloys. The results confirmed the viewpoint that the up-rise of △E in the later stage of fatigue experiment are due to the occurrence of coarse slip bands in the specimen, and is not due to the softening of the specimen associated with over-aging.Re-solution treatments were made in fatigue experiments of Al-4% Cu alloy. Judging from the behavior exhibited by the △E and T_m curves after each treatment, the conclusion may be drawn that the fatigued specimen can be made to recover to its original condition if the specimen is treated immediately after the up-rise of △E. However, if the specimen is treated a while after the up-rise of △E, the fracture of the specimen is sped up because of the occurrence of fatigue cracks in the specimen.Two conclusions having practical significance can be made on the basis of our experimental results: (1) It is possible to detect the formation of initial fatigue cracks through the method of measuring △E, because the occurrence of coarse slip bands is a prelude of crack formation; (2) it is possible to delay the occurrence of coarse slip bands and thus to raise the fatigue life through the method of alloying and heat treatment.