Effect of ultrasound on microstructure evolution of friction stir welded aluminum alloys
Effect of ultrasound on microstructure evolution of friction stir welded aluminum alloys
复制标题
超声波对搅拌摩擦焊铝合金显微组织演变的影响
DOI：
10.1016/j.jmapro.2020.05.005
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发表时间：
2020-08-01
影响因子：
6.2
通讯作者：
Ushioda, Kohsaku
中科院分区：
文献类型：
--
作者：
Hu, Yanying;Liu, Huijie;Ushioda, Kohsaku
研究了超声影响下Al-Cu合金搅拌摩擦焊的动态再结晶（DRX）过程，并与未施加超声的相同装置下生产的另一种接头进行了比较。超声对再结晶晶粒演化的影响主要依赖于局部热循环。对于高温下的搅拌区（SZ），超声处理显著提高了等轴晶的形核速率和生长速率。与无超声作用的SZ相比，UFSW接头SZ局部高角边界的胀形频率增加了2-4倍，产生了相当数量的细核。超声引入的多余空位是上述现象的内在原因。过量的空位增加了位错的爬升，大大加快了亚晶粒的迁移率，从而降低了UFSW的标准化形核标准，从而导致了DRX过程中较大的形核速率。超声增强了晶界位错的移动和晶界自扩散，促进了晶界的滑动和迁移，导致UFSW接头SZ内等轴晶的生长速度加快。
The dynamic recrystallization (DRX) in ultrasound affected friction stir welding (UFSW) was investigated using Al-Cu alloy and compared with another joint produced by the same setup but without applying the ultrasound. The effect of the ultrasound on the evolution of recrystallized grains was significantly dependent on the local thermal cycle. For the stir zone (SZ) exposed to high temperatures, both the nucleation rate and growth rate of equiaxed grains during DRX were significantly promoted by the ultrasound. Compared with the SZ without the effect of the ultrasound, the bulging frequency of the local high angle boundaries in the SZ of UFSW joint was increased to 2-4 times, producing a considerable number of fine nuclei. Excess vacancies introduced by the ultrasound were the intrinsic reason for the mentioned phenomena. The sub-grain mobility was radically accelerated due to the enhanced dislocation climb by the excess vacancies and thus the normalized nucleation criterion in the UFSW was reduced, contributing to a larger nucleation rate during DRX. Grain boundary sliding and migration were both facilitated by the ultrasound due to the enhanced movement of grain boundary dislocations and grain boundary self-diffusion, leading to a larger growth rate of equiaxed grains in the SZ of UFSW joint.