Aging kinetics of friction stir welded Al-Cu-Li-Mg-Ag and Al-Cu-Li-Mg alloys

• Published in: Materials & design 2016-11, Vol.110, p.60-71
• Main Authors: Sidhar, Harpreet, Mishra, Rajiv S.
• Format: Article
• Language: English
• Subjects: Aging (metallurgy); Aging kinetics; AGING MECHANISMS; Al-Cu-Li alloys; Alloys; ALUMINUM ALLOYS (50 TO 99 AL); Aluminum base alloys; COPPER ALUMINUM ALLOYS; Differential scanning calorimetry; Friction stir welding; FRICTION WELDING; HARDNESS; JOINTS; RECRYSTALLIZATION; SILVER ALLOYS (50 TO 99 AG); Silver base alloys; Transmission electron microscopy; Vickers microhardness; Welded joints; WELDING
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2016.07.126

Friction stir welding under ambient cooling conditions, using tool rotation rate of 800rpm and welding speed of 200mm per minute was carried out on 2195 and 2199 Al-Li alloys. Underwater welding was also performed on both the alloys using a pool on the top of workpiece. Post weld heat treatment for various durations was conducted to study the effect of alloy chemistry on aging kinetics in various metallurgical zones developed during welding. Vickers microhardness, differential scanning calorimetry, and transmission electron microscopy results showed that low dislocation density after recrystallization in weld nugget results in delayed aging kinetics for both the alloys. Ag containing alloy 2195 showed faster aging response compared to Ag-free alloy 2199. Coarse precipitates at grain boundary and in the grain interior were found responsible for loss of non-recoverable strength in heat affected zone for both the alloys. [Display omitted] •Underwater friction stir welding reduced the strength loss in heat affected zone and thermo-mechanically affected zone.•Low dislocation density was responsible for the delayed aging kinetics in case of alloy 2195.•Low dislocation density and absence of Ag was responsible for the extremely sluggish aging kinetics in case of alloy 2199.•Partial dissolution of T1 precipitates was responsible for the low strength in heat affected zone (HAZ) of 2195.•Full dissolution of Al3Li and partial dissolution of T1 phase were responsible for reduction in strength in HAZ of 2199.