I like aluminum! It’s silvery, it’s lightweight, it’s easy to drill, and best of all, it’s strong!
However, aluminum is finicky to work with. I prefer its use for bolt-together trailers rather than conventional welded trailers. Here’s why:
Most people are interested in aluminum for a homemade trailer to save weight. Unfortunately, because aluminum welds are so weak, you must use thicker-gauge material compared to steel. This cancels out most of the weight savings AND adds cost! So generally, if you’re welding a trailer, it just makes more sense to stick with steel.
Pros of Choosing Aluminum for a Trailer
Aluminum Is Impressively Strong
Most aluminum trailers are fabricated with 6061-T6 extruded structural aluminum, the most commonly available alloy and temper of structural aluminum in the United States.
6061-T6 has a tensile yield strength of about 40 ksi (thousand pounds per square inch) For reference, A36 steel, a mild steel used for angle iron or C-channel for trailer frames, only has a tensile yield strength of as low as 36,000 pounds per square inch! So aluminum can, in fact, be as strong or stronger than steel.
However, 6061-T6 aluminum pales in comparison to A500 or A513 structural steel tubing, rated for 46 ksi and 62 ksi yield strength, respectively. It’s also nowhere near as strong as steel I-beams, rated for 65 ksi.
Aluminum Is Corrosion-Resistant
As we all know, aluminum doesn’t rust. In fact, it oxidizes in the presence of air so quickly that it forms a protective coating against further corrosion.
While aluminum is still susceptible to harsh salts and some chemicals, such as salt water or road salts, its resistance to corrosion far exceeds that of carbon steel. Most trailers use raw mill finish aluminum; it’s rare to find anodized aluminum used on a trailer.
For that reason, most aluminum trailers don’t require any further painting or finishing – although, if you plan to use your trailer in a marine or coastal environment, you can certainly paint it for additional protection.
Aluminum Is Lightweight
It’s incredible that aluminum weighs just one-third of steel and yet can be just as strong! That’s why so many people are interested in aluminum trailers. A lightweight frame is easier to build, increases your vehicle’s fuel efficiency, and allows you to carry more cargo. If you drive a small tow vehicle, a lightweight aluminum frame might be the only way you can tow a small trailer or camper!
Aluminum Is Easy to Machine
If you’re building a homemade trailer, aluminum is much easier to cut, drill, and machine than steel.
- You can easily drill aluminum with regular HSS drill bits without cutting fluid.
- You can cut aluminum with a circular saw blade for plywood and non-ferrous metals.
However, structural aluminum doesn’t bend well. In fact, you should assume that bending 6061-T6 aluminum at all can compromise its strength and create stress cracks.
And welding aluminum is a different story entirely!
Cons of Choosing Aluminum for a Trailer
Aluminum Is Flexible
Some people equate rigidity with strength. That’s not quite accurate. A rubber strap is extremely flexible, yet very strong, whereas a thin icicle is rigid, but very brittle and weak.
Aluminum has one-third the modulus of elasticity as steel, meaning that it is about three times more flexible. That’s not necessarily a bad thing, but when it comes to our trailers, we don’t want the frame and tongue flexing much!
For that reason, aluminum trailers are designed with extra gussets, brackets, and other reinforcements. Designers prefer using box tubing over open profiles like iron or C-channel. Boxed profiles are much stiffer, which is essential when working with aluminum.
Aluminum Is Less Tough than Steel
“Tough” has a specific meaning to engineers. In layman’s terms, it means something can bend without breaking. A36 steel, for instance, is not as strong as 6061-T6 aluminum, but it can bend a lot before it breaks! Meanwhile, once 6061-T6 aluminum passes its yield strength and begins to bend, it will break very quickly.
This is a big reason most trailers aren’t made from aluminum. Many trailers, especially utility trailers, get overloaded at least a few times in their life. (Someone decides to pile all the shingles in the middle of the deck rather than spreading them out, for instance.) A steel trailer will usually bend before it breaks, but an aluminum trailer can catastrophically fail from the same load!
Engineers designing aluminum trailers account for this by incorporating a higher factory of safety. Unfortunately, while the trailer is safer, it’s also usually significantly heavier and more expensive.
Aluminum Doesn’t Have a Fatigue Endurance Limit
Engineers can debate about aluminum’s endurance limit and fatigue stress response for hours, but let’s keep it simple: Aluminum breaks down over time when loaded and unloaded. The heavier the load and the more cycles, the quicker it will break down.
Aluminum Doesn’t Weld Happily
Welding structural aluminum anneals the base metal in the heat-affected zone (HAZ), which means that the aluminum around the weld can lose up to 80% of its strength. Imagine if you lost 80% of your limbs (hint: you’d have less than one arm remaining).
That weakness next to the weld makes welded aluminum far more prone to cracking. In fact, aluminum welds are notorious for starting and perpetrating cracks. Many trailer builders, even skilled welders, refuse to build aluminum trailers because the welds are so finicky and so prone to failure.
Typically, trailer manufacturers use thicker material to compensate for the loss of strength in the welded region, but this drastically increases weight and cost.
I am a fan of using aluminum for bolt-together designs rather than welded designs. A bolted joint preserves the aluminum’s tempered strength without considerably increasing the overall weight.