Steel vs Alumninium

Bayou Boy

Adventurer
Most on an airplane is riveted and bolted together.
Some exotic friction stir weld surfacing now..... but most is bolted and rivited.
Surprisingly little welded on 10 Ton class part 25 jets
Very true.

However there are a ton of welded boats running around that essentially live in vibration due to the engine and waves.
 

ebrabaek

Adventurer
Very true.

However there are a ton of welded boats running around that essentially live in vibration due to the engine and waves.
Fully agree.
I have often wondered why not more planes are welded...... but I think rather than a lag of longlegivity..... it is so parts can be unbolted or rivited and replaced.

Lots of great boats holding up fine.
 

luthj

Adventurer
Aluminum welds return the heat affected zone to T0 (non heat treated condition). To restore tensile strength and fatigue resistance, the weld zone must be heat treated and artificially aged. This is a moot point if you are starting with T0 aluminum material though. For this reason aircraft use mechanical fastening methods with aluminum. Aluminum has a higher specific strength than steel (strength per unit weight) only when heat treated. In the annealed (t0) condition it actually has a slightly lower specific strength than steel.

For reference, giving a well controlled welding process (no excessive heat input), 6061-T6 will go from around 45ksi tensile strength, to 27ksi

A bolted 6016-T6 or similar alloy structure would be around half the weight of a steel one. Maybe a bit less, as you need to add margin for fatigue loading in aluminum.

A welded boat hull has much less point loading than a framed vehicle chassis. Boats also have less weight concerns, and can have significantly higher factors of safety.
 
Last edited:

old_CWO

Member
Properly done aluminum is really nice; good strength to weight, no rust and looks fancy to boot. It's harder to get good paint adhesion as an amateur but not impossible of course. Steel is typically cheaper and easier to repair or modify by backyard fabricators.

I like steel but mostly 'cause you can fix it with a hammer...
 

Alloy

Member
You mean like airplanes?
It would be hard to find a weld on a plane....lots of rivets though.

Rule of thumb......alum is 1/2 the strength of steel but 1/3 the weight.

Welding alum as well as creating the proper connections is 2x harder than steel.....without proper connections it will crack. Lost count of the number (cracked) of poor connections I've fixed.
 
Last edited:

Alloy

Member
A welded boat hull has much less point loading than a framed vehicle chassis. Boats also have less weight concerns, and can have significantly higher factors of safety.
Point loading happens when there isn't enough internal structure to support the hull plate for a given speed and weight. For this reason cracking happens alot.

Recreational (production line) boats have little to no additional strength because alum costs $$. To save (alum) weight builders will use sprayfoam.
 

kmacafee

Adventurer
An aluminum bumper saved me from serious injury in a rear end collision that totaled the vehicle. Sure, so would a steel bumper but at significantly more weight, not to mention greater corrosion risk. IMHO, aluminum done right is more than adequate for vehicle modification.
 

CampStewart

Observer
An aluminum bumper saved me from serious injury in a rear end collision that totaled the vehicle. Sure, so would a steel bumper but at significantly more weight, not to mention greater corrosion risk. IMHO, aluminum done right is more than adequate for vehicle modification.
The stresses that cause cracking of aluminum welds on a bumper are far less than those encountered by an aluminum trailer. Apples and Oranges
 

J-No

New member
Thx again all. Good points all around. Steel guy not responding. Did some measuring in garage, this may be stored outside. For that, leaning aluminum. No extreme use.
 

ottsville

Observer
Thx again all. Good points all around. Steel guy not responding. Did some measuring in garage, this may be stored outside. For that, leaning aluminum. No extreme use.
My steel trailer with a steel deck has been sitting outside uncovered for almost 20 years. Rolled a new layer of rustoleum on the deck last year, but other than that it's fine.
 

john61ct

Adventurer
Plenty of welded aluminum trailers for big boats out there, last fine for decades.

Just needs doing right, not skimping on material.
 

J-No

New member
Update—been talking to local-ish fabricator. Going steel—deposit sent today.
Thanks all for replies!!
 
Top