Materials Science and Engineering A 492 (2008) 250–254 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea The time–temperature–corrosion susceptibility in a 7050-T7451 friction stir weld C.S. Paglia ∗ , R.G. Buchheit The Ohio State University, Department of Materials Science and Engineering, 477 Watts Hall, 2041 College Road, Columbus, OH 43210-1179, USA article info Article history: Received 7 December 2007 Received in revised form 14 March 2008 Accepted 25 March 2008 Keywords: AA7050-T7451 Friction stir weld Time Temperature Corrosion susceptibility abstract The temperature gradient occurring for a short time during friction stir welding greatly affects the local- ized corrosion properties of welded 7050-T7451 plates. An immersion experiment in a salty solution was carried out in order to verify the influence of short-term post-weld heat treatments at temperatures sim- ilar to those taking place during friction stir welding on the corrosion behaviour of friction stir welded 7050-T7451. The experiment consisted of inserting thermocouples at different weld regions for the reg- istration of the temperature development with time, and partially immersing the welded plate in a salty solution at 480 ◦ C. In this manner, the weld experienced different temperature expositions at different locations. It was found that a temperature exposition above 180 ◦ C for 20 min significantly increases the general corrosion resistance of friction stir welded 7050-T7451. The re-exposition of 7050-T7451 friction stir weld to a time–temperature combination similar to that occurring during the welding process on the thermomechanically heat affected zones of the weld, significantly improves the corrosion properties and the environmental cracking resistance. After the short-term temperature exposition, the fracture location of samples tested in a 3.5wt.% NaCl solution moved from the corrosion susceptible thermomechanically affected zone to the heat affected zone. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Thermal treatments, applied in particular to aluminum alloys, can substantially vary the microstructure and the properties of the alloys [1,2]. Friction stir welding promotes a thermal tran- sient, which influences the time–temperature exposition of the microstructure in the welded region and in the adjacent zones of aluminum alloys [3,4]. During the relatively short time at which the original alloy microstructure is exposed (temperatures rang- ing from ca. 250 ◦ C to ca. 450 ◦ C), the microstructure undergoes a modification from dissolution to coarsening of the precipitates [5–7]. It is clear that, minute changes in the microstructure promoted by the friction stir weld thermal transients may largely affect the corrosion susceptibility of the different weld zones. This can be easily observed for welds where the most corrosion susceptible zone, appears to be the nugget-heat affected zone region [8–10]. Post-weld heat treatments have been applied to friction stir welded aluminum alloys plates in order to increase the corrosion resistance of the corrosion susceptible weld zones as well as the mechan- ∗ Corresponding author at: University of Applied Sciences of Southern Switzer- land, DACD, Trevano, CP 12, 6952 Canobbio, Switzerland. Tel.: +41 58 666 63 61, fax: +41 58 666 63 59. E-mail address: christian.paglia@supsi.ch (C.S. Paglia). ical properties [11–13]. Interrupted quenching experiments from solutionizing temperatures have also been carried out to study the time–temperature localized corrosion effects [14]. Neverthe- less, the exposition of friction stir welds to short time–temperature intervals, as it is during friction stir welding, has never been inves- tigated, in particular for aluminum alloy 7050-T7451 friction stir welds. Thus, the goal of this work is to clarify the relationship between time and temperature-localized corrosion susceptibility of a 7050- T7451 aluminum alloy friction stir weld. This work would like to verify, if short time post-weld heat treatments at temperatures reached during welding, may be an effective way to increase the corrosion resistance of the weld. 2. Experimental 2.1. Material Aluminum alloy 7050-T7451 plates with 10mm thickness. 2.2. Post-weld heat treatment set-up The set-up for the temperature exposure was based on that used in other investigations [14,15] and consisted of a salt pot containing a sodium nitrate–sodium chromate solution at 480 ◦ C. Thermocou- ples were inserted at different locations along the weld and the 0921-5093/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2008.03.039