The electrochemical corrosion performance of aluminum alloys grade 6082-T6 weld repair

Abstract

This research investigated the corrosion behavior of standard current metal inert gas weld repair for 6082-T6 aluminum alloy using ER5356 filler metal. The new and repaired (NW and RW) welds were studied. The welds comprised the weld metal (WM), the heat affected zone (HAZ) (solid solution and softened zones), and the base metal (BM). The study focused on investigating electrochemical corrosion using polarization and electrochemical impedance spectroscopy (EIS) methods in 3.5% NaCl solutions, especially in HAZ, including metallurgical and mechanical examinations. The BM containing an α-Al matrix with Al(Fe,Mn)Si and Mg₂Si phases exhibited the maximum hardness (70–104 HV_0.1). The WM hardness decreased (67–76 HV_0.1) with the α-Al, β-Mg₃Al₂, and Mg₂Si phases. Despite having comparable phases to BM, HAZs showed lower hardness (Solid HAZ: 70–82 HV_0.1) due to more intermetallic phases. The RW’s softened HAZ revealed the minimum hardness (52–63 HV_0.1) compared to that of the NW (55–70 HV_0.1). Besides, the tensile strength of the RW (179.7 MPa) was also lower than that of the NW (174.4 MPa) because of the reheating effect. The electrochemical corrosion results indicated that the BM exhibited the maximum corrosion resistance (the lowest corrosion current density (i_corr), the highest corrosion potential (E_corr), and the charge transfer resistance (R_ct)), followed by the HAZ and the WM, respectively. The softened HAZ demonstrated better corrosion resistance than the solid solution HAZ. Conversely, the over-aging effect reduced the softened zone’s pitting corrosion resistance (E_p) compared to the solid solution zone. The RW exhibited inferior corrosion resistance compared to the NW due to increased intermetallic phases, which was consistent with the mechanical results. However, the RW’s softened HAZ corrosion characteristics were inconsistent with its mechanical properties; its hardness and tensile strength were the lowest, but its corrosion resistance was not. Pitting corrosion was observed on the weld surfaces using the SEM.