Microstructural origins of mechanical and electrochemical heterogeneities of friction stir welded heat-treatable aluminum alloy

Abstract

In the present work, microstructural heterogeneities of friction stir welded EN AW 6082-T6 aluminum alloy were revealed with the help of optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrochemical heterogeneities of the welded joint was probed by electrochemical corrosion potential measurements. Microhardness and tensile tests were used to reflect heterogeneities in mechanical properties. The peak temperature and thermal cycles were examined and simulated during welding. The results showed that the heterogeneity of mechanical properties was determined by the nano-sized precipitates, while had little relationship with the micro-sized and submicro-sized deposits. The tensile fracture path was located at the minimum hardness zone where the β′′ precipitates have completely transformed to the β′ precipitates. Electrochemical experiments revealed that the corrosion potential was not homogeneous across the welded joint. The heterogeneity of corrosion performance was determined by the micron-sized excessive Si phase. In addition, the effect of nano-sized precipitates on the corrosion performance was attributed to the change in the solubility of the Si content in the Al matrix resulted from the precipitation, dissolution and transformation of the precipitated phase in HAZ.