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 o C and 800 o C 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 o C and 280 o C. 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.
I TRODUCTIOThe temperature developed during the friction stir welding (FSW) of high strength 7-xxx series aluminum alloys promotes a coarsening of precipitates and a widening of the precipitate-free zones, in particular within the heat affected zones of the weld [1,2]. These latter weld zones appear to be the most corrosion susceptible regions [3,4]. Recently, the effect of natural, artificial and RRA aging on the properties and structure of 7-xxx series aluminum alloys [5,6], and on the mechanical and corrosion properties of 7249 and 7075 aluminum alloys [7,8] as well as the effect of temperature and exposure on precipitates morphology, strength and plasticity [9] were investigated. In this concern, conventional post-weld heat treatments have been used to partially restore the properties of the welds. These treatments often reached solutionizing temperatures and the samples were subsequently subjected to re-aging processes [10,11,12]. A non-conventional post-weld heat treatment was also applied to AA 7075-T651 [13], obtaining an increase in the corrosion properties. This was mainly due to the local dissolution of precipitates, in particular along the grain boundaries. Nevertheless, short-term heat treatments that might modify the properties of the welds are currently on an initial investigation stage.Like the corrosion, the resistance to impact is an important property of engineering components subjected to dynamic loading. The temperature also control the fracture behaviour. The fracture proceeds, for ferritic alloys, through microvoid coalescence (ductile behaviour), adsorbing energy, or through cleavage, for brittle behaviours. In this latter case, the energy adsorbed decreases with a reduced toughness of the material [14]. The influence of notch severity and temperature on the impact were also tested for AA 7055. The fracture toughness of 45 o notched samples ...