Resistance of aluminum and aluminum alloys to nitric acid corrosion

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The behavior of aluminum and aluminum alloys in nitric acid is similar to that of steel in sulfuric acid: neither is resistant to dilute acids, but they are resistant to concentrated acids. Aluminum corrodes rapidly in dilute nitric acid with a concentration of less than 80%, whereas it exhibits good corrosion resistance at room temperature in concentrated nitric acid and fuming nitric acid with concentrations above 80%. In relatively dilute acids, stainless steel outperforms aluminum; in concentrated acids at temperatures slightly above room temperature, aluminum is superior to stainless steel. The corrosion rate of aluminum in concentrated acid at room temperature is less than 0.1 mm/year. Aluminum and aluminum alloys suffer the most severe corrosion in nitric acid of moderate concentration; the corrosion rate reaches its maximum value (3–4 mm/year) when the nitric acid concentration is between 20% and 30%. Dilute acids with a concentration of less than 0.5% cause only slight corrosion to aluminum and aluminum alloys (except aluminum-magnesium alloys).