Finite element simulation of corrosion of SS304 and Q235 dissimilar steel friction stir welded joints

In view of galvanic corrosion of dissimilar metal welded joints, based on principle of corrosion electrochemistry, parameters of potentiodynamic polarization curve and area ratio of metallographic structure were used as boundary conditions. Finite element analysis software COMSOL was used to predict corrosion behavior of FSWed joints of Q235 low-carbon steel and 304 stainless steel (SS304) dissimilar steel in different zones, and variation law of macroscopic and microscopic galvanic corrosion potential distribution and current density in different zones of welded joints was studied. The results showed that in macroscopic galvanic corrosion, the maximum corrosion depth was located at the junction of retreating side of SS304 (RS₃₀₄) and stirring zone (SZ), which was about 5 times that of base metal of Q235 low carbon steel (BM_Q235). Current density of all zones increased with the increase of corrosion time. In microscopic galvanic corrosion, the maximum corrosion depth was located at the junction of stirring zones on both the SS304 side (SZ₃₀₄) and the Q235 side (SZ_Q235), which was about 1.2 times that of BM_Q235. Moreover, the larger the area proportion of pearlite was, the worse the corrosion resistance was. The finite element model could be used to predict corrosion behavior of friction stir welded joints of dissimilar steels in different zones.