Malopheyev Sergey, Vysotskiy Igor, Zhemchuzhnikova Daria, Mironov Sergey, Kaibyshev Rustam
Laboratory of Mechanical Properties of Nanoscale Materials and Superalloys, Belgorod National Research University, 308015 Belgorod, Russia.
Materials (Basel). 2020 Sep 23;13(19):4246. doi: 10.3390/ma13194246.
This work was undertaken in an attempt to ascertain the generic characteristics of fatigue behavior of friction-stir welded aluminum alloys. To this end, different alloy grades belonging to both the heat-treatable and non-heat-treatable types in both the cast and wrought conditions were studied. The analysis was based on the premise that the fatigue endurance of sound welds (in which internal flaws and surface quality are not the major issues) is governed by residual stress and microstructure. Considering the relatively low magnitude of the residual stresses but drastic grain refinement attributable to friction-stir welding, the fatigue performance at relatively low cyclic stress was deduced to be dictated by the microstructural factor. Accordingly, the fatigue crack typically nucleated in relatively coarse-grained base material zone; thus, the fatigue strength of the welded joints was comparable to that of the parent metal. At relatively high fatigue stress, the summary (i.e., the cyclic-plus residual-) stress may exceed the material yield strength; thus, the fatigue cracking should result from the preceding macro-scale plastic deformation. Accordingly, the fatigue failure should occur in the softest microstructural region; thus; the fatigue strength of the welded joint may be inferior to that of the original material.
开展这项工作是为了确定搅拌摩擦焊铝合金疲劳行为的一般特性。为此，研究了铸造和锻造状态下可热处理和不可热处理类型的不同合金牌号。分析基于这样一个前提，即健全焊缝（其中内部缺陷和表面质量不是主要问题）的疲劳耐久性受残余应力和微观结构的支配。考虑到残余应力的幅度相对较低，但搅拌摩擦焊可使晶粒显著细化，因此推断在相对较低循环应力下的疲劳性能由微观结构因素决定。相应地，疲劳裂纹通常在晶粒相对粗大的母材区域萌生；因此，焊接接头的疲劳强度与母材相当。在相对较高的疲劳应力下，总应力（即循环应力加残余应力）可能超过材料屈服强度；因此，疲劳裂纹应源于先前的宏观塑性变形。相应地，疲劳失效应发生在最软的微观结构区域；因此，焊接接头的疲劳强度可能低于原始材料。
