Stress Corrosion Cracking Behavior of Friction Stir Welded Al 6061-T651

摘要

In the present study, corrosion behavior of friction stir welded (FSWed) Al 6061-T651 with varying welding parameters, including rotating and welding speeds, were examined. The 4 mm thick Al 6061-T651 alloy plates were friction stir welded. The resistance to corrosion was slightly improved, or at least did not decrease, for FSWed Al 6061-T651 alloy in 3.5 percent NaCl solution compared to the parent material. The effect of different welding conditions on the corrosion resistance was minimal. The micrographic and fractographic observations strongly suggested that the change in corrosion behavior of FSWed Al 6061-T651 was largely related to the clustering of coarse Mg_2Si precipitates, due to the whirling and casting action by severe plastic flow in the weld zone. Low welding speed and/or high rotating speed tended to encourage the plastic flow per unit time and consequently the clustering of coarse precipitates. The resistance to SCO in 3.5 percent NaCl solution was considerably higher for the FSWed Al 6061-T651 compared to that of the PM counterpart. The improved SCC resistance for the FSWed specimen was due to the fact that the stress corrosion cracks were enhanced at the boundary between the DXZ and the HAZ due to the greatest galvanic corrosion potential difference between the two phases, while the tensile fracture occurred at the other area where the strength level was the lowest.