Effect of Microstructural Constituents on Fusion Zone Corrosion Properties of GMA Welded AA 5083 with Novel Al-Mg Welding Wires of High Mg Contents

The corrosion behavior of fusion zones (FZ-1: 5.39 Mg-0.66Mn, FZ-2: 5.49 Mg-0.35Mn, and FZ-3: 5.72 Mg-0.32Mn) of AA5083 alloy welded with high Mg-containing Al-Mg filler wires has been systematically investigated. An extensive microstructural characterization was performed to evaluate the localized corrosion properties of the fusion zones. The potentiodynamic polarization test and salt spray test showed that the corrosion resistance decreases with increasing Mg content, therefore, the corrosion resistance of FZ-3 is lower than that of the FZ-1 and FZ-2. The electron microscopic analysis after intermittent corrosion test revealed that the eutectic beta-phase (Al3Mg2) was responsible for the initiation of corrosion. The corrosion behavior of each microstructural constituents was related to the dissolution potentials of the corresponding microstructures; hence, it forms galvanic couple with the Al matrix. Moreover, high Mg content in the filler wire lead to the formation of additional beta-phase in the fusion zone. However, intermetallics such as Al-6(Fe,Mn) and Mg2Si were significant only during the later stages of corrosion.