Corrosion Behavior Of Friction Stir Welded High Strength Aluminum Alloys

Friction stir welding (FSW), a relatively new solid state joining process, is used to join aluminum alloys of all compositions including alloys essentially considered unweldable. During FSW, a rotating tool provides a continual hot working action, plasticizing metal within a narrow zone at the join line, while transporting metal from the leading face of the probe to the trailing edge as the tool moves along the interface. Although melting does not occur during FSW, temperatures are sufficiently high and times at temperature sufficiently long to cause dissolution, nucleation, and/or coarsening of strengthening precipitates. The temperature-time profile changes with distance from the nugget causing a gradient in micro structure and precipitate morphology. The altered micro structure in the weld zone becomes sensitized in some high strength aluminum alloys. Results presented assess the pitting, intergranular, and SCC corrosion behavior of FSW 7XXX and 2XXX alloys. Progress in understanding the changes in microstructure responsible for the sensitization will be discussed. The presentation also will include evaluations of approaches for corrective measures.