Effects of Solution Heat Treatment on Friction Stir Welding Joints of 7B04-O Aluminum Alloy

Relationship between welding conditions, abnormal grain growth and mechanical performance in friction-stir welded 6061-T6 aluminum alloy

“…This undesirable phenomenon occurs during post-weld heat treatment and involves catastrophic growth of a few grains which finally consume almost entire weld zone. It has been observed in various aluminum alloys including 1 xxx [3][4][5][6], 2 xxx [7][8][9][10][11][12][13][14][15][16], 5 xxx [17][18][19][20][21][22][23][24][25][26][27][28][29], 6 xxx [30][31][32][33], and 7 xxx [11,[34][35][36][37][38][39][40][41] series, as well as in magnesium alloys [42][43][44][45], some steels [46][47][48][49], and even metal-matrix composites [50,…”

“…Within the stir zone, the abnormal microstructural coarsening typically initiates either at the upper weld surface or at the weld root [4,8,9,15,17,[19][20][21][25][26][27]31,[34][35][36]38,40,41,43,45,48,52,53]. Also, the grain growth at the advancing side (AS) is often more pronounced than that at the retreating side (RS) [8,25,27,30,36,38,43,48,52].…”

“…According to this theory, the abnormal annealing behavior is attributed to a combined effect of drastic grain refinement and dissolution of second-phase particles both occurring during FSW. Alternative explanations for the catastrophic grain growth include inhomogeneous microstructure distribution within the stir zone [20,31,40,48], precipitation of grain-boundary segregations [47,49], and increased mobility of particular grain-boundaries [6,44].…”

The Evolution of Abnormal Grains during the Heating Stage of a Post-Weld Solution Treatment in a Friction-Stir-Welded 2519 Aluminium Alloy

“…Nevertheless, despite the substantial grain growth at the weld root and the SAZ, the microstructure at the centre of the stir zone appeared to remain almost unchanged, which was indicative of relatively high thermal stability (Figure 3c). Previous studies have also observed abnormal grain growth in the periphery of the stir zone [8,9,15,18,[24][25][26]28,30,31,[40][41][42][54][55][56][57][58].…”

“…This has frequently been seen to lead to abnormal grain growth (AGG) in the stir zone, a phenomenon involving a significant coarsening of some grains, which tend to consume a considerable portion of the microstructure . This undesirable phenomenon has been reported for almost all heat-treatable aluminium alloys, including the 2xxx [7][8][9][10][11][12][13][14][15][16], 6xxx [17][18][19][20][21][22], and 7xxx [11,[24][25][26][27][28][29][30][31][32] series as well as their dissimilar combinations [30][31][32][33][34][35][36][37] that show similar characteristics.…”