Abstract: In this paper, the welding of 7020+7020 and 7020+6082 plates was designed and then the two kinds of welded joints were tested. The microstructure of the fusion zone, heat-affected zone and substrate of the welded plates was analyzed by OM and SEM, the microstructure and composition of the welded plates were analyzed by SEM, and the temperature field of welded plates was analyzed using a simulation software. The results show that corrosion starts from the heat-affected zone, the 7020-side temperature is higher and the cooling rate is slower when different materials are welded, resulting in the increase of grain size and the polarization of elements. As a result, the corrosion is more serious. MgZn₂ is precipitated on the grain boundary and the subgrain boundary, forming corrosion micro cells with the grain matrix and the surrounding depleted region. With the lowest potential, MgZn₂ is first corroded, causing corrosion to occur and expand in the heat-affected zone, and making the heat affected zone of the 7-series welded joint most sensitive to intergranular corrosion.