Environmental Cracking and Impact Investigations after Short-Term Temperature Treatments: 7050-T7451 Friction Stir Weld

The influence of short-term heat treatments on the environmental cracking and impact properties of a 7050-T7451 friction stir weld were investigated. Prisms, cut transverse to the welding direction, were exposed for minutes at temperatures between 100 oC and 800 oC in an oven or exposed to a propane torch flame and/or water / air quenched. A significant increase in the environmental cracking resistance (ductility ratio from 0.2 to 0.9) was observed for samples exposed to temperatures below the solutionizing limit, but between 240 oC and 280 oC. The fracture location changed from the “soft” heat affected zones to the nugget. Furthermore, the weld exhibited a decrease in the Charpy impact adsorbed energy as compared to the weld unaffected parent metal. An increase in the temperature improved the adsorbed energy, while a temperature decrease promoted the brittleness and reduced the adsorbed energy. The flow contours, also called onion ring bands, present within the nugget, represented a preferential fracture path during impact. The high temperature treatments followed by water quenching did not significantly improved the resistance to impact.