Development of grain structure during friction stir welding

Recrystallization mechanisms during friction stir welding/processing of aluminum alloys

“…Altogether, DRV, GDRX and DDRX have been cited as the mechanisms that can account for grain refinement in FSW/P in aluminum and various aluminum alloys [11,12,20,24,25]. The two former mechanisms are consistent with the current understanding of recrystallization in aluminum in light of its high stacking fault energy.…”

“…Further, the observations were made on the transverse plane after the tool had passed, a plane of observation employed in a majority of studies. Only a few studies have been performed using ''quick-stop'' and tool extraction techniques, wherein the tool is withdrawn and the material rapidly quenched prior to examination throughout the nugget/SZ [11,12,25,26]. Such studies have highlighted the possibility that a combination of models is necessary to describe the different microstructures observed.…”

“…Microscopy techniques have included microtexture and orientation imaging microscopy (OIM) methods, as well as optical and transmission electron microscopy (TEM) techniques. For example, a study designed to examine microstructures at locations surrounding the FSW tool has shown that subgrains form ahead of the tool and develop greater misorientations at locations nearer the tool [25]. However, regions in the nugget that were adjacent to the pin tool were difficult to characterize because electron backscatter diffraction pattern quality becomes severely degraded due to residual strain.…”

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“…Ligas de alumínio, por apresentarem as características desejadas, vem sendo objeto de pesquisa [1][2][3][4][5][6][7][8][9], em especial ligas de alumínio-lítio [10][11][12], que mantém essas características mesmo em baixas temperaturas. A adição de 1% em peso de Lítio gera, aproximadamente, uma redução de 3% na densidade da liga, além de aumentar o módulo elástico em cerca de 6% [13].…”

“…A variação microestrutural decorrente do processo de FSW em ligas de alumínio tem sido amplamente descrita na literatura [1,4,7,8,11,15]. De forma geral, a região da lente de soldagem (nugget), mostrada na Figura 5C, tem microestrutura de grãos equiaxiais, de dimensões refinadas (da ordem de alguns micrômetros), formados por recristalização devido ao efeito conjunto, nessa região em particular, de altas deformações e temperaturas [15].…”