Aluminium vs Brass Fittings: When to Switch and When Not To

I get asked this question regularly from engineers who are designing systems and have a choice: aluminium or brass? The honest answer is that both materials are excellent in their respective domains, and the decision becomes clear once you work through five specific variables. Let me give you the framework.

Variable 1: The Fluid or Gas Being Carried

This is the first filter and it immediately eliminates one material for many applications.

Choose brass when carrying: Potable water (especially with WRAS/NSF certification requirements), natural gas or LPG, steam, hydraulic fluid (most types), or any fluid where the fitting must be certified by a third-party body for that specific service.

Choose aluminium when carrying: Dry compressed air, nitrogen, inert gases, clean pneumatic fluid, instrument air. In these services, aluminium is lighter, cheaper, and performs equally or better than brass.

Do not use aluminium with: Strong alkalis (pH >9), hydrofluoric acid, acetic acid, mercury, or any fluid that specifically attacks aluminium. Do not use aluminium in direct contact with potable water for plumbing (no approved certifications exist for aluminium in this application in most markets). Do not use aluminium with wet steam.

Variable 2: Weight Sensitivity

Aluminium is roughly one-third the weight of brass per unit volume. If the application is weight-sensitive — mobile equipment, handheld tools, aerospace, automotive, racing — aluminium wins on weight every time. If the fitting is permanently installed in a fixed location, weight is largely irrelevant to the engineering decision.

Variable 3: Corrosion Environment

Variable 4: Pressure and Temperature Requirements

Brass (CW617N) has an ultimate tensile strength of approximately 370 MPa and maintains this strength up to 150°C. Aluminium 6061-T6 has UTS of approximately 310 MPa but — importantly — de-rates more significantly with temperature than brass.

At 150°C, 6061-T6 retains approximately 60–70% of its room-temperature strength. At 200°C, the retained strength drops below 50%. Brass at 150°C retains approximately 85% of room-temperature strength.

For applications with continuous elevated temperature service, check the aluminium alloy's temperature-strength curve before specifying. For standard compressed air or pneumatics at ambient to 60°C, this is not a concern.

Variable 5: Certification Requirements

This is the variable that often makes the decision for you: regulated applications require certified fittings, and the available certifications differ significantly between materials.

Brass certifications available: WRAS (UK potable water), NSF/ANSI 61 (USA potable water), NSF/ANSI 372 (lead-free), WaterMark (Australia), DVGW (Germany gas), CE (EU pressure equipment), UL/FM (fire suppression), ISO 9001, and many others.

Aluminium certifications available: ISO 9001, CE (pressure equipment for industrial use), specific aerospace standards (AS9100). Notably absent: WRAS, NSF, WaterMark for potable water. Aluminium is simply not approved for potable water service in any major market.

If your application requires a specific third-party product certification, identify that requirement first and let it determine your material. No amount of engineering argument will substitute for a missing regulatory approval.

The Cost Comparison — Done Honestly

Aluminium raw material is cheaper than copper or zinc (brass constituents). CNC machining of aluminium is faster. The cost per part for an aluminium fitting is typically 20–35% lower than an equivalent brass fitting of the same geometry.

But this comparison ignores total system cost. If the aluminium fitting requires anodising for corrosion protection, add that cost. If it requires dielectric isolation from adjacent copper or steel components, add that cost. If it has a shorter service life in a marginal environment and needs earlier replacement, add that cost.

The honest cost comparison is total cost of ownership over the system design life — not just unit price. In many applications, aluminium's lower unit price plus appropriate surface treatment equals or beats brass on total cost. In applications where brass's superior corrosion resistance eliminates surface treatment needs and maintenance replacements, brass can be the better total cost option despite higher unit price.