Solubility effects of Sn and Ga on the microstructure and corrosion behavior of Al-Mg-Sn-Ga alloy anodes

• Sn is soluble between 400 and 550 °C in Al-0.5Mg-0.08Sn-0.08Ga alloy.
• Lower corrosion was observed at 450 °C solutionizing as Sn solubility is highest.
• Higher polarization resistance observed for the alloy at 450 °C solutionizing.
• Solubility of Sn reduces the self-corrosion, while Ga activates the surface.
• Uniform distribution of Sn has a major contribution in corrosion than Ga.

The microstructure and corrosion behavior of Al-0.5Mg-0.08Sn-0.08Ga (wt%) anode material solutionized at different temperatures ranging from 400 to 550 °C is studied. Thermal analysis reveals that Sn is soluble in the Al alloy in this temperature range. Microstructural observation shows maximum solubility of Sn above 450 °C. Electrochemical investigations in 3.5 wt% NaCl and 9 M NaOH solution reveals lower corrosion and hydrogen evolution rates for the specimen solutionized at 450 °C. Though Sn is soluble above 450 °C, the corrosion slightly increases at higher solutionizing temperatures due to the segregation Ga at the surface. The corrosion and hydrogen evolution rate are higher when Sn is present as precipitate and causes localized (pitting) type of corrosion. On the contrary, presence of Sn in solid solution improves the corrosion resistance and decreases the hydrogen evolution rate. Hence, it can be concluded that the presence of Sn in solid solution is essential for reducing the corrosion rate and the distribution of the Sn plays a major role in the corrosion behavior of Al-Mg-Sn-Ga alloys.

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