Improvement in Galvanic Corrosion Resistance between AA5083 and Pure Fe or Stainless Steels in Diluted Synthetic Seawater Due to Anodizing

Abstract

Because of worldwide emission gas control, the weight reduction for automobiles has been widely required. Multi-material structures for automobiles, in which several materials like steels and aluminum alloys are utilized, are effective methods as techniques to reduce the weight; however, the galvanic corrosion becomes a serious problem for the joints between steels and aluminum alloys. In our previous research [1], galvanic corrosion damages on pure aluminum coupled to pure iron or stainless steel were prevented by anodizing because the anodic oxide film on pure aluminum becomes thicker with increasing anodizing time and voltage. For aluminum alloys, intermetallic particles on aluminum alloys become the initiation sites of localized corrosion; therefore, anodizing behavior on intermetallic particles should be important for preventing the galvanic corrosion damage on aluminum alloys. In this research, anodizing conditions were determined to prevent the localized corrosion generation on AA5083 when pure iron or stainless steels were coupled to AA5083. Pure iron, type 304 stainless steel, type 430 stainless steel, and AA5083 (Al-Mg alloy) were prepared as specimens in this research. Diluted synthetic seawater (200 mg/L Cl-, pH 8.2) was used as the electrolyte for electrochemical measurements. The electrode area was ca. 10 mm2. Ag/AgCl (3.33 M KCl) was used as the reference electrode. Galvanic currents and electrode potentials of aluminum alloy electrode were measured via a zero resistance ammeter. The distance between steel and aluminum alloy electrodes was kept at 10 mm. Additionally, anodizing was treated to AA5083 in various anodizing voltage and time conditions. The galvanic currents and electrode potentials of AA5083 coupled to pure iron were measured. The galvanic currents were anodic currents during the measurements, and the small oscillations of galvanic currents and electrode potentials were generated. After the measurements, many pits and filiform corrosion were observed on AA5083. The localized corrosion was induced by ennoblement of the electrode potentials of AA5083.[1] Takumi Kosaba, Izumi Muto, Yu Sugawara: Effect of anodizing on galvanic corrosion resistance of Al coupled to Fe or type 430 stainless steel in diluted synthetic seawater, Corros. Sci., 179 (2021), 109145.