Mechanical and corrosion properties of friction stir welded joints of Al-Cu alloy 2219-T87

Abstract

Abstract In the present study, 8.1 mm thick AA 2219–T87 plates were joined by friction stir welding (FSW) process. Welds were characterized by using micro hardness survey, tensile testing, face bend, root bend tests, optical microscopy (OM), transmission electron microscopy (TEM) and salt fog test (ASTM B117) at different pH values and spraying times. Hardness survey across the joint revealed that weld nugget is the softest region and it is also found that tensile failure occurs in the nugget. Tensile testing of the transverse welded joints showed that high efficiency (> 75 %) joints could be produced. The friction stir welds subjected to the surface bend showed 1800 bend ductility, whereas in the critical root bend the cracks were initiated at a bend angle in the range of 30–400. Transmission electron micrographs obtained from various regions of the weld indicated that almost all strengthening precipitates dissolved in the nugget region while partial dissolution of precipitates occurred in the thermomechanically affected zone and coarsening occurred in heat affected zone. However, the losses in hardness in the nugget due to dissolution of precipitates and the negation of work hardening by recrystallization were compensated to a large extent by the strengthening due to the grain refinement in the nugget, which explains the high joint efficiencies exhibited by these welds. It was observed that the welds possessed much better corrosion resistance in basic and neutral solution than in acidic solution. It was found that corrosion attack was greater in the base material than in weld metal at all pH values and spraying times. It has been concluded that friction stir welding has a significant effect on mechanical and corrosion properties of the welds.