Aluminium use in car parts

[mlewis]

Hey guys thinking of using some aluminium pipe in my project mini for things like the front control arms and link bars.

im thinking of using a 2mm wall thickness to help give it some strength. My question is tho is there any reason why you cant use aluminium for these kind of parts. Mate of mine suggested making the front subframe out of aluminium but im thinking it wont be strong enough

Any thoughts and advice on the subject is much appreciated

[Dell'Orto]

I don't know about the legalities of ali tube, but plenty of cars use cast ali for control arms, it's definitely beneficial.

[mlewis]

its purely a track/event car rather then trying for cert and road use. obviously the wieght is low which is the upside just dont know to much about the strength/durability

[Stott69]

I think you would strugle, ali goes soft once heated and then needs ageing to regain it. Have a chat with your cert guy, but the hastle may out weigh the benifits.

[pc]

its purely a track/event car rather then trying for cert and road use. obviously the wieght is low which is the upside just dont know to much about the strength/durability

If you don't have the engineering background to work it out, don't do it. You will end up risking many other people's well being as well as your own.

[mlewis]

so either make them in chromoly or mild/high tensile steel?

[Grrrrrrr!]

Chromoly will need heat treating, as will most high tensile steels. And they need to be welded properly, with the correct filler rod. Having a suspension arm fail at speed would be bad for you, and the guy racing beside you. You'll probably find that you can buy arms already made overseas, they will almost certainly be cheaper than getting it done as a one off locally.

[mlewis]

thats what i was thinking but its for the mini so they are going to be rather small in comparison to most premades

[Grrrrrrr!]

Minis have such a huge following someone will make arms to suit.

try minisport.com for starters.

[fivebob]

Chromoly will need heat treating, as will most high tensile steels.

Why?

[mlewis]

i need them to replace the ek control arms ive got currently, so instead of the nasty elbow factory honda items i want to replace them with 2 straight pipes in an A-frame design with rod eyes on each end

[mlewis]

So wanting to use 2 of these http://www.minisport.com/21a1879-standa ... rm-rh.html (or similar looking ones) in an A-frame pattern to mount between hub and subframe instead of a nasty honda elbow

[Grrrrrrr!]

Cant remember exactly what the reasons are, formation of the wrong phases in the weld HAZ would be my guess.

[fivebob]

You might want to normalise the welded area after welding but that's about all you'd need.

The only problem I can ever recall with welding CrMo is hydrogen embrittlement, but IIRC that was only an issue if you chromed the part.

[mlewis]

so general consensice is use either chromoly or a steel rather then alluminium unless im getting a experienced engineer to make them for me?

[Grrrrrrr!]

Found something which explains why heat treating 4130 is required.

http://bbs.homeshopmachinist.net/threads/32367-Does-4130-steel-tubing-need-to-be-heat-treated-for-maximum-strength?p=408104#post408104

Apparently gas welding makes it much less of an issue, as discussed further down that thread.

[fivebob]

It doesn't say anything about it being required. Just that it is stronger if you do (and possibly more brittle).

4130 chrome moly tubing is used extensively in aircraft construction and also in motorcycle frame manufacture. To my knowledge it is both gas and mig/tig robotically welded. The only thing that is done to it is to normalise the welded area by heating the surrounding area to a very dull red then slowly withdrawing the heat and allowing it to cool in air.

You don't see huge failure rates with this method in very safety conscious industries and AFAIK there is no mandated requirement in the aircraft construction industry, ergo it is not required if constructed properly.

Either way heat treatment for a small part like a control arm is not hard or expensive it you really want to do it.

[Dell'Orto]

Also have you spoken to Shane Mendoza about his Mini subframes? He might be able to give you some good ideas

[Adoom]

thats what i was thinking but its for the mini so they are going to be rather small in comparison to most premades

For a mini.... As has been mentioned, there are lots of off the shelf options available if you have the money. But just get all the photos and measurements you can and go off to your local engineer, it will probably be cheaper than importing it from the UK.

Machine the aluminium parts so that they do not require welding. So, no problem with heat treating or proper welding technique.

</MY OPINION>

[fivebob]

Seems that in general the same procedures can be applied when TIG welding CrMo tubing...
From The FAA regulations welding section

TIG Welding 4130 Steel Tubing Welding 4130 with TIG is not much different than welding other steels as far as technique is concerned. The following information generally addresses material under 0.120-inch thick.

Clean the steel of any oil or grease and use a stainless steel wire brush to clean the work piece prior to welding. This is to prevent porosity and hydrogen embrittlement during the welding process. The TIG process is highly susceptible to these problems, much more so than oxy-acetylene welding, so care must be taken to ensure all oils and paint are removed from all surfaces of the parts to be welded.

Use a TIG welder with high-frequency starting to eliminate arc strikes. Do not weld where there is any breeze or draft; the welds should be allowed to cool slowly. Preheating is not necessary for tubing of less than 0.120-inch wall thickness; however, postweld tempering (stress relieving) is still recommended to prevent the possible brittleness of the area surrounding the weld due to the untempered martensite formations caused by the rapid cooling of the weld inherent to the TIG process.

If you use 4130 filler rod, preheat the work before welding and heat treat afterward to avoid cracking. In a critical situation such as this, engineering should be done to determine preheat and postweld heat treatment needed for the particular application.

Weld at a slower speed, make sufficiently large fillets, and make them flat or slightly convex, not concave.

After the welding is complete, allow the weldment to cool to room temperature. Using an oxy-acetylene torch set to a neutral flame, heat the entire weldment evenly to 1,100F - 1,1200F; hold this temperature for about 45 minutes per inch of metal thickness. The temperature is generally accepted to be a dull red in ambient lighting. Note that for most tubing sections, the temperature needs to be held for only a minute or two.

This process is found in most materials engineering handbooks written by The Materials Information Society (ASM) and other engineering sources. When working on a critical component, seek engineering help if there is any doubt.

I think the take home message is that you should research and understand what you are doing before undertaking such a task, or get someone who knows what they're doing to do it for you.