Is aluminum frame better than stainless steel?

In just about any corner of the engineering world, the choice between aluminum vs. stainless steel boils down to durability vs. price. Simple, right? 

In a vacuum, those are great starting points. However, they don’t tell the whole story when it comes to modular structural framing systems.

Comparisons of stainless steel framing to aluminum systems are closer and more nuanced than your textbooks once told you. Let’s take a heavy-duty look at these heavy-duty products to truly understand where and when to use them.

Note: This article doesn’t cover carbon steel, but these ones do:

Stainless Steel vs. Aluminum Framing – Material & System Differences 

In applications like medical carts and racking systems, stainless steel framing almost always uses welded connections. Aluminum framing systems generally consist of extrusions connected mechanically.

Beyond this basic point, what else do you need to know?

1. Strength-weight ratio
2. Durability
3. Ease of use
4. Price
5. Cleaning
6. Magnetism

1. Strength-to-Weight Ratio

Stainless steel structural members aren’t really all that structural. Generally speaking, they can hold up an everyday assembly, but nothing truly heavy-duty like a 4” carbon steel tube could. Usually, when designers use stainless, it’s for reasons besides strength.

Aluminum is also popular for reasons beyond strength, but that doesn’t mean you discount it as a structural material. Yes, aluminum is lightweight and soft, but it’s short-sighted to say aluminum is therefore weak. Aluminum framing’s strength-to-weight ratio is actually higher than that of the average stainless steel grade:

304 Stainless
Steel

Aluminum
6005 T5

Tensile
Strength

73,200 psi
(505 MPa)

39,900
(275 MPa)

Density

~7.93 g/cm3

2.81 g/cm3

Strength Ratio

~63

~99

Because aluminum extrusions hold more weight than you’d think, it’s a go-to material for structural builds where weight reduction is critical. On the other hand, stainless steel offers superior overall strength, but at the cost of increased weight.

If you end up choosing aluminum framing, you must also understand the difference between traditional and heavy-duty systems. The well-known T-slot extrusion system uses pinned connections that are weak at the joints. Newer, self-aligning aluminum systems are also extrusion-based, but the brackets and connections are much more highly engineered, making joints a strong point of the assembly.

In short: If your build is heavy-duty go with stainless. If your build is heavy-duty, but can’t be heavy, go for self-aligning aluminum framing.

2. Durability

Cost and other factors aside, both aluminum and stainless steel are great for reducing maintenance downtime on a production line. You’ll find some quirks with each, so don’t assume they’re interchangeable.

Mechanical

Welded stainless steel frames come with rigid, fixed connections that offer reliable long-term stability. They’re tough and resistant to deformation under fairly heavy loads.  

Again, stainless steel doesn’t exist to be mechanically perfect – it was never intended to be as durable as carbon steel. But it does maintain a valuable trait of steel-based frames – it bends and cracks slowly, rather than crashing suddenly.

Aluminum systems – the old ones, at least – don’t give you this warning. It doesn’t bend well, so when failure happens, it’s quick and catastrophic.

Again, results vary depending on the aluminum building system. If you install T-slot framing in or around vibrating machinery, it quickly loses its alignment and invites disaster down the line. However, self-aligning aluminum framing uses fixed connections just like welding, offering a predictable outcome for structural projects.

Aluminum is more prone to dents and scratches. Unless you’re super-stressed about aesthetics, there’s no reason to disqualify aluminum based on mechanical performance – as long as you avoid T-slots.

Environmental

This is where stainless steel shines. Its addition of chromium to the standard steel formula grants it excellent corrosion resistance. 

Upon exposure to oxygen, the chromium creates a durable, nonreactive barrier on stainless steel framing. This type of metal framing protects against:

• Acid
• Alkaline solutions
• Harsh weather

Aluminum can perform many of these same tasks – just not as well. It creates its own naturally occurring layer – zinc oxide – that offers a nice level of corrosion resistance. Self-aligning systems use architectural-grade anodization to make aluminum even more viable in heavy-duty framing projects.

Temperature is another environmental factor to watch out for. Due to its high melting point, stainless steel has better fire resistance than aluminum, making it a great option for machines working in fire-risk areas. On the opposite end of the spectrum, stainless is more likely to become brittle in extreme cold, making aluminum the better choice in freezer-type environments.

3. Ease of Use

There are three stages where you can judge a structural framing system’s user-friendliness: assembly, movement, and modification.

Stainless steel framing is tough to work with, from start to finish.

• Assembly –

  Welding stainless steel is fairly difficult, as it retains more heat than standard steel and can distort if you aren’t diligent. Welding isn’t mistake-friendly, so you’re stuck with any screw-ups unless you cut and reweld the problem spot.
  
  

• Installation & transportation –

  Stainless steel framing is heavier, so you may need extra people or equipment to move it. This sucks time and energy from your operation.
  
  

• Modification – Any repurposing of the frame requires someone to cut the old stuff out and weld in the new parts. At least you know you’re getting a precise and level result (if your welder is skilled enough).

Welding is a challenge with both stainless and aluminum structural framing systems. While aluminum is softer and easier to form, it conducts 5x more heat than stainless, making the skill curve even steeper. And if you mess up, not only will the material be distorted, it’ll also lose some of the benefits it gained during heat treatment. 

However, there’s good news – you shouldn’t need to weld aluminum framing, ever.

Instead, use aluminum extrusion framing for what it’s meant for – providing a modular system that’s easy to assemble and adjust without having to cut and reweld.

Thanks to its lightness, aluminum is a great choice if you need to move a mobile cart or restructure a robotic stand. You’ll rarely need a whole team to lug around your system. Assembly and disassembly is possible with one tool and one person. Modular systems also save shipping costs because of their lightness and ability to be shipped in pieces and assembled on-site without specialized labor.

And if you spring for a high-end (self-aligning) system over traditional T-slots, you’ll make assembly even simpler:

• No need to square & level
• Attaining precision happens on the first try
• 50% faster assembly

4. Price

Cost is a tricky thing in manufacturing. Aluminum and stainless steel structural framing each offer some nice perks both short- and long-term.

Short-Term Costs

It takes effort to look this good. Stainless steel carries a hefty price tag because it requires intense processing to achieve its stellar defensive properties. That often relegates its use to applications where corrosion concerns outweigh cost concerns.

Think about the effort it takes to prepare a stainless steel framing system for use:

Stainless Steel Frame Welding Process

Sourcing

Clean & dry surface

Secure trained welder

Clamp pieces to be welded

Transport material to welder's facility

Weld

Measure & cut steel

Clean again

Bevel at least one edge for joining

Transport weldment back to customer

Precision comes with a cost, too: The more accurate you want the weld, the more money you’ll pay. It’s a time-consuming process not many can do – not only is the labor cost high, the downtime cost may also be problematic if you frequently struggle to find welders with the necessary skills.

At the raw-material level, aluminum production requires less energy, resulting in a lower price tag. Also, because you’ll need less material (by volume) to achieve strength equal to stainless steel’s, an aluminum assembly needs fewer components.

That’s part of why T-slot extrusion use is so widespread, though its archaic connection system limits the savings. To gain the most value from aluminum’s strength-weight ratio, stick with the highly engineered connections of self-aligning systems. We’ve seen them reduce the bracket count by up to 75% in equivalent T-slot frames.

Long-Term Costs

Welding creates a permanent, stiff bond – one that resists vibration and movement. This fact, combined with the low-maintenance nature of stainless steel’s surface, gives stainless some serious long-term value in most use cases.

Both materials keep themselves in pretty good condition corrosion-wise, though in extremely harsh conditions aluminum may need more upkeep. However, the right aluminum modular system can outperform stainless steel in high-intensity mechanical applications (i.e. vibratory environments).

Once again, with aluminum you’re looking at very different results depending on your investment and your application. Every time a typical low-cost 80/20 aluminum frame has to be moved (or is moved unwillingly by vibration), it loosens and becomes misaligned. Someone will need to routinely tighten the connections – this maintenance cost could add up to $1,000 or more monthly per machine. And that’s not factoring in the loss of production while you wait for scheduled or unplanned fixes.

If total cost of ownership is your thing, try a self-aligning system instead. Its mechanically locking connections mimic welded carbon steel so well it actually can out-steel steel.

5. Cleaning

Some industries must pay special care to run a clean operation – literally. For both manufacturers and end users, concerns may include:

• Cleanroom – use of acceptable materials for preventing dust & other particle infiltration
• Food prep – clean surfaces without bacteria living in nooks & crannies
• Medical equipment – protecting health-compromised patients

Stainless steel surfaces are sterile and nonporous. What’s more, stainless doesn’t require additional treatment or coating post-installation – just a little cleaning as need be. Many designers specify stainless steel modular enclosures because they need to easily wipe down the guarding and keep bacteria from collecting on it.

For industries with stringent standards, stainless is hard to beat … if you can afford it.

T-slots and other extrusion systems do have those dangerous nooks and crannies, but they’re easy to clean. Also, aluminum has above-average corrosion resistance, so you’re not losing much there. The main downfall of extrusion components in squeaky-clean applications is that any open slots will collect dust. If this is a concern for your application, consider a self-aligning system, which can use threaded inserts to cover the slots.

6. Magnetism

Magnetism plays a significant role in certain machinery builds and industries. This is most obvious in health care manufacturing, where magnetism:

• Interferes with MRI machines & CAT scans
• Is harmful to pacemakers
• Can’t even exist in the steel rebar on the floor!

Aluminum modular framing is never magnetic. Sadly, most stainless steel grades are magnetic, save for anything in the austenitic series (though cold-forming 301 and 304 can turn them partially magnetic).

Because of the dangers of magnetic attraction (and the price of stainless), more medical structural equipment may be aluminum-based in the future. Today’s medical carts are all stainless steel and plastic – an aluminum cart with no ferrous material would be a huge win.

There’s opportunity for innovation down to the individual pieces of hardware. T-slot extrusion framing systems still use steel nuts and bolts, but moving toward aluminum alternatives could make them even more advantageous in no-magnet zones like hospitals.

More to the Story on Aluminum & Steel Framing

What stainless steel framing lacks in affordability, it makes up for in long-term value. It’s hard to dent, corrode, or get dirty – and it never causes contamination issues.

You also can mine plenty of long-term value – at a lower up-front cost – from aluminum extrusion building systems for a variety of applications. Aluminum shines in its superior strength-to-weight ratio, ease of use, and viability in nonmagnetic and cleanroom applications.

Ultimately, the choice depends on the specific requirements and priorities of the project at hand. Visit our blog for more tips on machine and frame building, plus more specifics on self-aligning systems: