Chemical Resistance Ratings for 5000 Series Aluminum Exposed to Alkalis and Acids

The 5000 series aluminum alloys are rated Good to Excellent in near-neutral environments (approximately pH 4–9), Poor in strong alkalis (pH > 10–12), and Poor to Fair in strong mineral acids. Within the family, 5083 and 5052 perform similarly in most acid/alkali exposures because both rely on the same alumina passive film; the difference is marginal and application-specific. The practical selection rule is not “which 5xxx alloy is more acid-resistant,” but “whether the specific chemistry, concentration, and temperature fall inside the passive window at all.”

The Governing Mechanism: A Passive Film With a Narrow Comfort Zone

All aluminum alloys resist corrosion through a naturally forming Al₂O₃ passive film. This film is stable over a pH range of roughly 4 to 9; outside that window, the film dissolves and the exposed metal corrodes rapidly. The film is amphoteric—attacked by both strong acids and strong bases—so the 5000 series inherits the same fundamental limitation as every other aluminum family.

Within the passive window, the 5000 series is among the best-performing aluminum families. Wrought Al-Mg alloys show high resistance to corrosion in marine and many chemical environments, and they are more resistant than the 6xxx series to salt water and certain alkaline solutions such as sodium carbonate and amines.

Rating Scale and Summary Table

Acid Side: Where the Risk Is Concentration- and Type-Dependent

The 5000 series does not have a single “acid rating.” Performance depends on whether the acid is oxidizing or reducing, and at what concentration.

Strong mineral acids are the clear failure zone. Hydrochloric acid is explicitly identified as a poor environment for aluminum, particularly below 40% concentration, alongside environments contaminated with heavy-metal salts or mercury. In acidic chloride solutions, 5052 develops stress corrosion cracking at pH below 1.0, and the oxide film’s protective effect becomes strain-rate dependent in the pH 1–12 range.

The notable exception is concentrated nitric acid. Because HNO₃ is strongly oxidizing, it reinforces the passive film rather than dissolving it; concentrated nitric acid is specifically listed as non-attacking to aluminum.

For 5083 specifically, the corrosion mode shifts with acid strength. In strong acids, uniform dissolution occurs across the surface; in weak acids, the attack is localized as pitting at inclusions and second-phase particles, with correspondingly lower mass loss.

Alkali Side: The Sharper and More Consistent Boundary

Alkalis are, on balance, the more predictable hazard for the 5000 series. The passive film is soluble in alkaline solutions, and accelerated attack begins above roughly pH 8.5–9, becoming severe above pH 10–12.

The mechanistic difference between acid and alkali exposure matters for design. In strong alkaline media, 5083 undergoes uniform dissolution. In near-neutral to mildly alkaline solutions, the surface can retain a less protective but stable Al(OH)₃ layer; at pH 12, selective aluminum dissolution becomes dominant, and Mg(OH)₂ formation can produce a compact, fully passive surface on the Al₃Mg₂ phase. This means that mild alkalinity can be tolerated in some formulations, but the margin is narrow and should not be extrapolated without specific testing.

One practical inhibitor note: in moderately alkaline water solutions, silicate inhibitors—as found in dishwasher detergents—can reduce corrosion of aluminum. This is relevant for cleaning and process-water specifications, not for the chemical cargo itself.

5052 vs. 5083: The Difference Is Smaller Than the Headlines Suggest

The compositional contrast between 5052 (roughly 2.2–2.8% Mg) and 5083 (roughly 4.0–4.9% Mg plus Mn and Cr) is often presented as a marine-corrosion story, not an acid/alkali story. In neutral saltwater, the higher magnesium and manganese content of 5083 gives it an edge in strength and marine service. In acid and alkali media, that same compositional difference does not translate into a categorically better rating.

Both alloys sit in the same passive-film-limited regime. 5083 shows elevated corrosion rates in both acidic and alkaline fretting conditions compared to neutral, with a lower friction coefficient at pH 7 and higher friction in both acid and alkali. 5052 shows SCC susceptibility only at pH below 1.0 or above 12.0 under slow strain rates—a relatively wide window in which the oxide film still mediates behavior.

The practical implication: do not select 5083 over 5052 on the expectation of better acid/alkali resistance. Select 5083 for strength and marine performance; select 5052 for formability and cost. For chemical resistance within the passive window, both are adequate; outside it, neither is a solution.

Quick Reference: Practical Selection Rules

Key Takeaways

• The 5000 series is rated Excellent within pH ~4–9, Poor in strong alkalis, and Poor in strong mineral acids. The rating is governed by the alumina passive film, not by the magnesium content within the family.

• 5083 and 5052 do not differ meaningfully in acid/alkali resistance. 5083’s advantage is strength and marine performance; selecting it for chemical resistance is a misapplication of the alloy difference.

• The failure mode changes with pH: strong acids and strong alkalis produce uniform dissolution in 5083, while weak acid/alkali environments produce localized pitting with lower mass loss.

• Concentrated nitric acid and ammonia solutions are exceptions to the general acid/base rule and should not be treated as aggressive without specific evidence.

• The boundary is sharper on the alkaline side (attack above roughly pH 8.5–10) than on the acid side, where concentration, acid type, and chloride co-presence all shift the outcome.

• For any exposure near the pH 4 or pH 9 boundary, a coupon test in the actual chemistry and temperature is more reliable than a family-level rating.