Influence of Solution Treatment and Artificial Aging onFracture Load of Friction Stir Welded Lap Joints of AA2014-T6

Abstract High strength aluminium alloys (2xxx and 7xxx) are widely used for many applications. Particularly, aircraft and automobile industries. The fabrication of this alloy is little bit difficult using traditional welding process. It produces porosity, alloy segregation, partially melted zone etc. In last few decades, these alloys are welded using a solid-state welding process, friction stir welding. However, the strength of the alloy is more than 80% of the base material strength. Although, the FSW joints have lowest hardness in the weld region due to heterogeneous properties in the microstructure. The lowest hardness region is the soft region that is the fracture-originating region during tensile test. Several techniques were used to enhance the lowest hardness region properties such as the aging process, the solution treatment process, cryogenic treatment in joints. In this research, the solution treatment followed by artificial aging on lap shear strength of friction stir lap-welded joints were performed. The heat-treated joints were compared with welded joints. From the experimental results, the heat-treated joints yield higher lap shear strength than the as welded joints. The reason for the higher lap shear strength was reprecipitation of precipitates in the welded joints during an artificial aging process. However, the aluminium matrix retains fine precipitates by the solution treatment process (under rapid cooling).