Structure-property correlation of friction stir welded AA 5083

Abstract

Aluminum Alloy AA 5083 due to its inherent properties like corrosion resistance, high ductility and higher strength to weight ratio is nowadays used in fast attack crafts, structural components of the ship and cryogenic tanks. Fusion welding techniques like Gas Tungsten Arc Welding (GTAW) are currently employed to join the aluminium used for structural application. Recently, a novel green solid-state welding technology known as Friction Stir Welding (FSW) has gained popularity. In the current work, the efficacy of friction stir welding over Gas tungsten arc welding was investigated by studying the mechanical properties such as strength, impact toughness as well as critical properties such as fracture toughness in terms of crack tip opening displacement (CTOD) and fatigue strength in terms of fatigue crack growth rates (FCGR). Both the welding process resulted in a defective weld joint; however, the latter has a defect under permissible limits. Porosity, in case of GTAW, was detected by X-ray radiography while kissing bond in case of FSW was not detected by X-ray radiography. The results showed that the strength of the FSW joint was higher than GTAW joint but lower than the parent material due to the presence of defects. Impact toughness and CTOD values for FSW joint were 57 Joules and 0.37 mm followed by base material with 38 Joules and 0.26 mm and least for GTAW with 18 Joules and 0.11 mm, even with the presence of kissing bond in the FSW joint. FCGR in case of FSW joint was marginally lower than that of GTAW joint. For both welding processes crack closure effects were significant for a/w ratio smaller than 0.6, but crack closure effect was more pronounced in FSW than GTAW. Therefore, it is evident that FSW joint with kissing bond defect showed superior properties than porosity contained GTAW joint. Considering structural applications, FSW is more suitable to weld AA 5083 than GTAW. Keywords: Friction Stir Welding (FSW), Gas Tungsten Arc Welding (GTAW), Crack Tip Opening Displacement (CTOD) and Fatigue Crack Growth Rates (FCGR).