A new project has you looking at structural metal framing systems.
You know many use welded steel, while a smaller number use extruded modular aluminum. Others use a combination with a welded steel base and extruded aluminum guarding.
While steel framing has long been the assumed must-have for structural support, engineers today are discovering the hidden quality and value potential of aluminum frames. Both methods have strengths and weaknesses – and even systems in the same aluminum family perform very differently – so which is right for your project?
Steel framing systems use pieces welded together to form structurally sound joints. Aluminum framing systems snap together modularly with extruded, T-slotted components or – when exceptional quality is necessary – self-aligning, non-T-slot components.
When choosing a system, consider your application’s needs for:
In cases where there are stark differences in performance between traditional extrusions and T-slot alternatives, we’ll mark them in red.
| Up-Front Affordability | Long-Term Affordability | Quality | |
| T-Slot | HIGH | LOW | LOW |
| Welded Steel | MEDIUM | MEDIUM | MEDIUM |
| Self-Aligning Extrusion | MEDIUM | HIGH | HIGH |
It’s true: Steel is a brute-force material, and aluminum is more of an engineered solution.
A welded steel profile offers higher tensile and yield strengths than aluminum extrusions of the same shape. For applications where high-load bearing capability is a must and weight doesn’t matter, welded steel is the way to go.
A variety of heat treatments are available to increase the material’s strength. However, heating and cooling around the weld joint can distort nearby components, putting added stress on the assembly.
Case closed, right? How much weight could an extrusion possibly hold with such a soft material?
Actually, aluminum extrusions’ strength supports many structural framing systems today without fear of failure. That’s why you can’t weigh (no pun intended) strength without also considering criteria #2 below.
But first, a few more strength considerations:
Why can’t you evaluate types of structural framing systems without factoring in weight? Because steel is about 3x as heavy as aluminum:
As the density values show, welded steel assemblies are much heavier. For projects that require lightweight structural design, think of criteria #1 and #2 as a ratio:
This ratio means steel is best for applications where strength and durability matter more than weight – such as bridge construction.
Extruded aluminum materials are lighter – so much so that they’re “stronger” pound-for-pound:
This allows your structural framing design to be lighter in weight while achieving the same strength results as steel. Or, the same amount of weight with higher strength results!
This makes extrusions ideal for products where lightweight design is vital, such as in aerospace applications. Additionally, using lightweight material, you need fewer components to support the structure, often providing better operator access.
There are two factors to consider when evaluating the useful lifetime of a system: structural integrity and environmental resistance.
“A steel resolve …”
“A steel will …”
There’s a reason people use this material as a metaphor for endurance.
Welded steel’s higher yield strength means it withstands greater loads over time. A rigid material, welded steel notably survives better in applications where vibration is persistent, as it uses no fasteners that could come loose.
In engineering, just about every advantage comes with a “yeah, but …” In steel’s case, that’s exposure to saltwater or other corrosives, which can make sharp, flaky profiles out of a once-flawless frame. In some applications – especially outdoors – welded steel requires coating or galvanizing to pass the test of time.
Other considerations include:
“Are aluminum extrusions durable?”
A loaded question. It’s time to break out the compliment sandwich.
First, the good: At no extra charge, aluminum provides a surface finish with superior corrosion resistance to even galvanized steel. This is because a protective oxide layer naturally forms on aluminum during exposure to the elements.
Now, onto the bad – and with traditional extrusion framing, there’s a lot of it.
On the raw material level, aluminum’s fatigue properties are poor compared to steel. On the assembly level, things really fall apart – literally.
A T-slot system is a simple and easy-to-manufacture technology that while versatile, has many engineering limitations. Put the frame on a vibrating or cycling application, and it loosens over time. Put stress on a small area, and the frame starts to yield.
Traditional T-slots require regular realigning to maintain a semblance of precision. This downtime to fix the system only does so much – it’ll still need replacement long before a welded structure.
Back to the positive! Self-aligning extrusion systems borrow engineering concepts from aerospace and trucking to eliminate wiggling and weakening. These advanced T-slot alternatives offer …
… to create bonded connections that stay stiff as a weld, even during long periods of vibration or cyclic loading.
And because of these connections, you can assume the assembly will act like a welded structure. That opens the possibility of an FEA, which is impossible to do effectively with traditional T-slots because of all the variables.
You have little room for error when welding, drilling, and cutting. Simply put, it’s tough to rework a completed assembly made from welded steel.
Repurposing and repairing steel-based framing systems often require outside help, adding weeks to your downtime.
Say you want to add a horizontal cross-member 6 months after purchase so you can mount some equipment. There’s no snap-on solution, so you have to:
When something damages your steel framing, adjustments are just as tedious.
Even repurposing is a hassle. Steel is less portable due to its weight, so moving it to another space or facility takes a lot of effort.
Modular aluminum profile systems allow you to attach or remove components anywhere, anytime. There’s less pressure to design the ultimate assembly that’ll last for eternity.
The modular customizability makes structural aluminum extrusions valuable for products that might need changes after installation. Want to mount a control panel to your year-old structure? With T-slot extrusions, it’s simple:
All of this is possible for a single, average-skilled worker to complete with hand tools. If you need to move the build, it’ll take less effort to tear down and move the lightweight extruded framing.
Advanced, self-aligning framing extrusions are fundamentally similar to T-slots – no need to drill or tap holes. However, the auto-aligning features take value a step further.
The parts of a self-aligning system come on and off even faster and easier than traditional T-slots. More importantly, you can do this over and over and maintain perfect precision.
Because it’s hard and brittle, steel is harder to manipulate.
All of this takes more effort when the material has low machinability and formability ratings.
Aluminum is soft and easy to form without compromising its sturdiness. You can create intricate shapes with wall thicknesses as low as 0.06”.
The lightweight nature of aluminum also makes extrusions easier to work with, since they require less effort to move through the production process.
Of course, you may not need to form anything – the library of premade T-slot parts may suffice for your design. There are several thousand bars and other shapes, with many profiles available precut.
Note that self-aligning aluminum extrusion framing systems come in far fewer shapes because the technology hasn’t been around as long. There’s a chance your project will need a custom-made component.
At face value, aluminum framing components cost more than welded steel profiles due to the complexity of the extrusion process and the higher raw material cost.
However, that surface-deep advantage doesn’t tell the whole truth.
To judge the true cost of steel structural framing, consider how the other criteria factor in:
These same performance criteria impact the cost of aluminum framing too:
There’s much more to the “steel vs. aluminum” debate than raw strength and material cost.
Structural metal framing systems made with welded steel, standard extrusions, and advanced extrusions each have a few selling points:
The moral is this: Don’t limit aluminum to where your old assumptions tell you it’s OK to use. Premium solutions sometimes come at a premium price, so weigh your up-front budget vs. your need for long-term structural and production stability.
For more tips on modular structural design, see our resource center: