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After welding, aluminum tanks often have residual flux, which can be corrosive and detrimental to the integrity of the material if not properly removed. A 5 percent solution of nitric or sulfuric acid is effective in neutralizing and removing flux from aluminum. This is because these acids can dissolve the flux residue without causing significant harm to the aluminum itself, making them suitable for cleaning applications post-welding.

In contrast, acetone, water, and alcohol do not possess the necessary reactivity to effectively break down and remove flux. Acetone and alcohol are excellent solvents for certain substances but are not sufficient for metallic flux residues. Water, while often used for rinsing or general cleaning, cannot neutralize or dissolve flux components effectively, especially if they are of a chemical nature that requires an acid for proper removal. Thus, the 5 percent solution of nitric or sulfuric acid is the recommended choice for ensuring that an aluminum tank is properly cleaned after welding.