Corrosion Behavior of 2219 Aluminum Alloy Base Metal and Welding Joints

The corrosion behavior of base metal of 2219 aluminum alloy and its friction stir-weld (FSW) joint and tungsten inert gas (TIG) joint was investigated by exfoliation corrosion test and potentiodynamic polarization curve test. The corrosion patterns and mechanism of above three materials were analyzed by making comparisons of corrosion mass loss, electrochemical corrosion property and micro-morphology of surface and cross-section after corrosion. The results show that the base metal had the largest corrosion rate, the lowest corrosion potential and the biggest corrosion current. The corrosion resistance of the weld or nugget of two joints was almost the same, and better than that of the base metal. The nugget of FSW joint was the best one. According to the classification of corrosion patterns, the base metal was exfoliation corrosion, the weld of TIG joint showed intergranular corrosion, and the nugget of FSW joint was pitting corrosion. The corrosion of the base metal and the welding joints was related with precipitated phase. The larger the size of precipitated phase was, the more obvious the galvanic effect was. The precipitated phase of the weld of TIG joint was along the dendritic boundary and showed the lower galvanic effect than the base metal due to its smaller size; on the contrary, the nugget of FSW joint had an improved performance of corrosion as a result of mechanical stirring which made the precipitated phase smaller and distributed uniformly.