Originally Posted by 5-90

You're getting dims called out - which is good. That's half of your question.

"DOM" means "Drawn Over Mandrel" - it's different from rolled/welded tubing in that it doesn't have a seam (it also usually doesn't have scale - so it doesn't need to be pickled - and there's more control over ID and OD.)

Material would be indicated by an AISI alloy number - it's a four-digit number that tells you what family of alloying elements are used (first two digits) and how much carbon is in the steel (decimal fractions of a percent - last two digits.)

For instance, AISI 1020 is a mild steel, unhardened, with .20% carbon by weight (a decent general-purpose steel.) If there is an "L" in the middle, it's got a percentage of lead added. "S" indicates sulphur. (Ex. 10L20 or 10S20.) Either sulphur or lead would be added to increase machinability.

For your application, you may want to go with a 41xx steel - it's the milder chrome-molybdenum steel. It provides strength advantages (which you'd need for a suspension member - particuarly column strength) and it welds well - and it's the easier to work between 41xx and 43xx.

If you don't want to spend that much money (41xx/43xx can get spendy!) going with a 12xx or 13xx steel isn't a bad idea - but ramp up the wall thickness accordingly. If the ID is critical, this means you'd have to go up an OD size to get a thicker wall. You may also have difficulty finding DOM in mild steels, but it's out there.

DOM can be identified "in the field" with a visual check - HREW/CREW (Hot Rolled Electrically Welded/Cold Rolled Electrically Welded) steel tubing does have a visible seam - made more visible by the HAZ inherent in welding. It also tends to have a "flash" inside the seam that is not drawn out after welding - which makes the seam quite obvious. HREW/CREW tubing shouldn't be used in applications where it is subject to forces in flexion - the seam forms a discontinuity, and is therefore a stress riser.

AISI - American Iron & Steel Institute. Governing body for alloy composition and nomenclature in the US.
CREW - Cold Rolled Electrically Welded. Typically no scale, but suffers from the "seam" flaw. In this process, the metal is heated - but not to the "transformation point" of the alloy. There is usually still some scale in the HAZ (q.v.,) but not overall like HREW/hot rolled steel.
DOM - Drawn Over Mandrel. The mandrel sets the ID of the tubing, the die sets the OD. This is usually a "cold" draw, so little to no scale. There is also no weldment/seam.
HAZ - Heat Affected Zone. Every weld has this, unless the part is heat-treated after welding (annealed and rehardened) to eliminate it. Every weld. In everything.
HREW - Hot Rolled Electrically Welded. The material is heated to above the "transformation temperature" before forming, which leads to the formation of an oxide scale during cooling. This typically requires pickling (an acid wash, mainly) to remove before finishing or welding. Scale may be removed locally using a wire wheel or cup brush.

Originally Posted by 5-90

Depends on stresses and environment.

For LCAs, I'd not want to use it - it tends to gouge when drug over something, instead of scrape. This compromises the strength of the part rather quickly.

For UCAs, it's doable - although you'd want a thicker wall than you'd want for steel to preserve column strength.

For steering linkage, there's not a lot of reason it couldn't work - as long as the steering is up out of the way (Over-The-Knuckle comes to mind.) Same complication as for LCAs.

And, for any use undercar, the aluminum gets a good hard anno (clear or coloured) after machining, so be sure to allow for the thickness of the anno job in your machining and fabrication (anno grows "half in and half out" - a .010" thick anodise will make the part .005" larger on the relevant dimensions. So, if you use a .010" thick anno inside a hole, the hole will come out to be .010" smaller - .005" on each side.)

For anything wanting extreme strength, I'd probably go with 41xx or 43xx gas-welded using a carburising flame (which is what those alloys were originally formulated for anyhow - it allows gas-welding with minimal post-heat-treatment and preserves strength in the HAZ.) For parts where aluminum is doable, 6061-T4 is a good general-purpose alloy, then you can go up to -T6, 7075-Tx, or some of the 2xxx-series alloys (which tend to approach mild steel in strength. A good structural aluminum alloy can be as strong as 12xx or 13xx steel, with less weight!)

Before you think mild steel is useless, bear in mind that most OEM axle halfshafts are 1541 steel...

Originally Posted by 5-90

I'm not as familiar with aluminum alloys as I should be - but I do agree with your choices. Throw a hard anno on it for environmental protection, and you're set (yes, aluminum corrodes. Just not very quickly... Like oxide coatings on steel, an anno is a controlled corrosion if the material. This for the uninitated...)

You're right about saving weight with aluminum - but you also have to consider the reduced strength. There's a point of diminishing returns when you're trying to save weight, and you end up having to use enough material that the wegiht advantage begins to evapourate... This is where design comes into play!

Originally Posted by fantic238

Yes, infact it would have sense if all the upgraded parts of a build, including bumpers and crossmembers, would be in Aluminium. The weight reduction would be significant in this case. Just the control arms is useless.
Regarding the design, who said that the control arm must be a tube? That's what i do for a living, and i came up with a couple of nice ideas, including composite materials.

Originally Posted by 5-90

Aren't the OEM CAs stamped steel U-channel? They stamp the things and then weld bushing sleeves in, as I recall. The control arms need not be overly strong - just need to be able to accept a bushing to allow for slight relative motion between the parts (control arm-frame, control arm-axle) to prevent stress cracks.

My big objection to aluminum control arms has already been stated - aluminum tends to gouge, where steel just scrapes. Given a choice, I'd take steel for anything running that close to the ground. Weight can be saved elsewhere, where durability is less of a concern. Strength/weight ratio is not the only consideration (as you probably know - but others do not) when selecting material for a given application...

Originally Posted by fantic238

The bushing sleeves are just pressed in lol, but they work well..