7075-T6 Aluminum Links

[MStudt]

I'm playing around with the idea of making some 7075 aluminum LCA's that are adjustable on both ends. Is this something that you guys would be interested in? They would be 1-3/4" OD, and drilled and tapped with LH & RH threads. Pricing maybe around the $400 mark.

 

[snivilous]

How's the cross section compare to stock links? Why not run 6061 or a different alloy?

 

[JeepKiller]

I'm assuming this is for the pair? How are you going about making them?

 

[MStudt]

How's the cross section compare to stock links?

For the rears, not the fronts. But, the cross section for the 7075 would have a larger diameter, and they'll be solid links rather than hollow tubing. 6061 has about half the tensile strength as 7075, and you'll only be saving about $20 in overall cost/price. I'd still make them from DOM as well, but going with aluminum would be easier to tap. You can get a solid bar, drill it, and tap it with ease. A 2 foot lower link would only weigh around 5lbs. If I wanted to drill and tap DOM I'd have to get a thicker wall like something around .375 to be able to use 1-14 thread without compromising the strength. A link made with that would be 10+ lbs.

I'm assuming this is for the pair? How are you going about making them?

That would be for a pair. I'd still need to finalize the pricing, and select what ends I want to use. I'll be making them as well. I'll be using my lathe to center bore them, and the drill tap them to LH & RH thread. I'd be able to do them for the uppers and lowers. I'll have to check on the panhard to make sure I have a long enough bed to be able to drill & tap them.

The 1-3/4 diameter for the lower links would be plenty strong, and they'll have more elasticity than DOM.

 

[JeepKiller]

Seems interesting, I'd like to see some pictures when you make themz

 

[MStudt]

Seems interesting, I'd like to see some pictures when you make themz

I'll most likely make them for myself first so I can get some pictures up, and see how they work. I just want to make sure the interest is there before I start yet another project.

 

[snivilous]

For the rears, not the fronts. But, the cross section for the 7075 would have a larger diameter, and they'll be solid links rather than hollow tubing. 6061 has about half the tensile strength as 7075, and you'll only be saving about $20 in overall cost/price. I'd still make them from DOM as well, but going with aluminum would be easier to tap. You can get a solid bar, drill it, and tap it with ease. A 2 foot lower link would only weigh around 5lbs. If I wanted to drill and tap DOM I'd have to get a thicker wall like something around .375 to be able to use 1-14 thread without compromising the strength. A link made with that would be 10+ lbs.

I was just figuring since your yield strength of 6061 is still higher than mild steel and you don't get any stiffness increase with 7075 it wouldn't make any difference. Why would would you have to run a thicker wall on steel for the same size tap? I like the idea and they would look pretty sweet!

 

[tH1e swiN1e]

Im always interested in mods.... show me pics and take my money!!

 

[MStudt]

I was just figuring since your yield strength of 6061 is still higher than mild steel and you don't get any stiffness increase with 7075 it wouldn't make any difference. Why would would you have to run a thicker wall on steel for the same size tap? I like the idea and they would look pretty sweet!

It would be very close tapping DOM that is 1-1/2 with a .250 wall to 1-14 thread. I'd need to drill the DOM to 15/16, and then tap. I suppose it would be OK since you'll be tapping into the solid steel. I just figure with everyone else starting to go with aluminum that I should give it a shot to see. There's a lot of upfront cost up front, and I'm debating if it's worth it or not.

 

[Nelsonmd]

From an engineering standpoint, I don't think Al links is a good material for this application.

1. First off, threading Al is just dumb IMO. Al threads never seem to survive well, even in non-stress applications. I don't think the Al is strong enough to even handle the preload in the long term. 7075 is a decent alloy for standing up to the stresses, but it's still not steel.

To expand on this, it is a risky situation to thread a very stiff, hard, and strong material to a soft and relatively weak material. The threads will easily cross thread, and the steel over time will dig into the Al, yield the Al, and you will soon end up with the Al threads failing.

This is a designed situation for things like lug nuts, where you thread a soft steel lug nut onto a strong, hardened steel stud, so that overtorquing causes the nut to rip off without damaging the stud, which is hard to replace. But in this situation, the lug nut material is still steel, not Al, it's just a softer steel. You still have the fracture toughness, the UTS and the yield strength that is sufficient for the application.

Also, the strain hardening of steel is beneficial to mitigating the continual yielding of the threads. Al doesn't do this.

2. I think the application is wrong for aluminum. The links are not just high stress, but they see impacts when you hit bumps and rocks and stuff like that. If you are threading the Al tubes onto something like a heim joint, then I would think that the threads will get torn out pretty easily as the Heim joint has no compliance and will directly transfer all the stress right into the Al

If you were threading it onto a steel race with rubber bushing like the stock LCA's, then that might mitigate this a bit, but I still think it's a lot more risk than just using steel.

I think if you did FEA on this, you would see some major stress concentrations around where the steel joint threads into the AL tube.

3. The Al will not survive impacts nearly as well at steel would. Especially if you're going to use tubes and not solid bars, the Al will deform much more easily if you bottom it out on a rock or something, and once it is dented/bent/deformed, it will fail much quicker than a bent/dented steel tube. 4340 steel has more than double the fracture toughness of 7075 Al. Other steel alloys go even higher than that (up to around 200, vs Al alloys peaking around 30). Steel handles damage way better than aluminum.

4. What's the advantage of the Al over steel? Steel is so easy to weld, so resilient to impact, has high fracture toughness, and is so cheap. I don't think you'll be saving much weight in the end on this, and it won't be cheaper, so what is the marginal benefit?

Don't mean to piss in your coffee, but some materials are just not correct for certain applications.

 

[snivilous]

From an engineering standpoint, I don't think Al links is a good material for this application.

1. First off, threading Al is just dumb IMO. Al threads never seem to survive well, even in non-stress applications. I don't think the Al is strong enough to even handle the preload in the long term. 7075 is a decent alloy for standing up to the stresses, but it's still not steel.

To expand on this, it is a risky situation to thread a very stiff, hard, and strong material to a soft and relatively weak material. The threads will easily cross thread, and the steel over time will dig into the Al, yield the Al, and you will soon end up with the Al threads failing.

This is a designed situation for things like lug nuts, where you thread a soft steel lug nut onto a strong, hardened steel stud, so that overtorquing causes the nut to rip off without damaging the stud, which is hard to replace. But in this situation, the lug nut material is still steel, not Al, it's just a softer steel. You still have the fracture toughness, the UTS and the yield strength that is sufficient for the application.

Also, the strain hardening of steel is beneficial to mitigating the continual yielding of the threads. Al doesn't do this.

7075 has double the tensile yield of A36 mild steel, granted the young's modulus is 1/3 that of the steel but if designed correctly that's no issue (obviously since stiffness = EI, so a proportionate I value negates the 10000ksi MOE

2. I think the application is wrong for aluminum. The links are not just high stress, but they see impacts when you hit bumps and rocks and stuff like that. If you are threading the Al tubes onto something like a heim joint, then I would think that the threads will get torn out pretty easily as the Heim joint has no compliance and will directly transfer all the stress right into the Al

If you were threading it onto a steel race with rubber bushing like the stock LCA's, then that might mitigate this a bit, but I still think it's a lot more risk than just using steel.

There are plenty of steel into aluminum applications, again if designed right there is no issue. The biggest issue imo is galvanic corrosion because of the valance difference between steel and aluminum (though you never mention this). You seem to be throwing lots of terms around without any review of the design parameters, you can make anything as strong as you want if designed right. Hitting rocks is a big deal, yes, but as previously stated if your I term is high enough then the lower E won't matter (which is why I asked initially what his cross section was since obviously you have a 4th power increase in round cross section moment of inertia of a round section).

I think if you did FEA on this, you would see some major stress concentrations around where the steel joint threads into the AL tube.

3. The Al will not survive impacts nearly as well at steel would. Especially if you're going to use tubes and not solid bars, the Al will deform much more easily if you bottom it out on a rock or something, and once it is dented/bent/deformed, it will fail much quicker than a bent/dented steel tube. 4340 steel has more than double the fracture toughness of 7075 Al. Other steel alloys go even higher than that (up to around 200, vs Al alloys peaking around 30). Steel handles damage way better than aluminum.

Agreed, again it's all design based and considering there's nothing fancy about the stock links you can easily make stronger ones out of Al

4. What's the advantage of the Al over steel? Steel is so easy to weld, so resilient to impact, has high fracture toughness, and is so cheap. I don't think you'll be saving much weight in the end on this, and it won't be cheaper, so what is the marginal benefit?

Don't mean to piss in your coffee, but some materials are just not correct for certain applications.

Agreed, but figure that 99% of people just want some fancy bling and don't really give a shit about the engineering properties which is why people make aluminum links and arms (Icon comes to mind initially). Obviously steel is easier to work with, but it's the cool factor people are buying and if they lose a little weight then great for them.

My counter-arguments above, I won't buy anything but think aluminum stuff looks cool and it can easily be designed and engineered to be stronger than the stock links.

Also funny enough I was finishing putting together some new beadlocks yesterday which are aluminum but have grade 8 fasteners and the instructions say NOTHING about anti seize and that you should replace the fastners if they are ever removed. But it doesn't take a genius to know that the aluminum will fail long before the grade 8 ever will and you could easily run stainless fastners or a lesser strength bolt, and obviously whoever designed those wheels didn't account for the galvanic corrosion between the steel fastners and aluminum wheel. I went and put anti seize over everything and then modified their torque spec to suit the lubrication. So yes, some companies run steel into aluminum but on the flip side they don't seem to do any engineering--just like 99.9% of the companies in the offroad segment.

 

[MTD]

From an engineering standpoint, I don't think Al links is a good material for this application.

1. First off, threading Al is just dumb IMO. Al threads never seem to survive well, even in non-stress applications. I don't think the Al is strong enough to even handle the preload in the long term. 7075 is a decent alloy for standing up to the stresses, but it's still not steel.

To expand on this, it is a risky situation to thread a very stiff, hard, and strong material to a soft and relatively weak material. The threads will easily cross thread, and the steel over time will dig into the Al, yield the Al, and you will soon end up with the Al threads failing.

This is a designed situation for things like lug nuts, where you thread a soft steel lug nut onto a strong, hardened steel stud, so that overtorquing causes the nut to rip off without damaging the stud, which is hard to replace. But in this situation, the lug nut material is still steel, not Al, it's just a softer steel. You still have the fracture toughness, the UTS and the yield strength that is sufficient for the application.

Also, the strain hardening of steel is beneficial to mitigating the continual yielding of the threads. Al doesn't do this.

2. I think the application is wrong for aluminum. The links are not just high stress, but they see impacts when you hit bumps and rocks and stuff like that. If you are threading the Al tubes onto something like a heim joint, then I would think that the threads will get torn out pretty easily as the Heim joint has no compliance and will directly transfer all the stress right into the Al

If you were threading it onto a steel race with rubber bushing like the stock LCA's, then that might mitigate this a bit, but I still think it's a lot more risk than just using steel.

I think if you did FEA on this, you would see some major stress concentrations around where the steel joint threads into the AL tube.

Haha yeah, but those stress concentrations apply to steel too

3. The Al will not survive impacts nearly as well at steel would. Especially if you're going to use tubes and not solid bars, the Al will deform much more easily if you bottom it out on a rock or something, and once it is dented/bent/deformed, it will fail much quicker than a bent/dented steel tube. 4340 steel has more than double the fracture toughness of 7075 Al. Other steel alloys go even higher than that (up to around 200, vs Al alloys peaking around 30). Steel handles damage way better than aluminum.

He is using bar stock, and I would'nt worry about fracture toughness nearly as much as fatigue, though it is a good point

4. What's the advantage of the Al over steel? Steel is so easy to weld, so resilient to impact, has high fracture toughness, and is so cheap. I don't think you'll be saving much weight in the end on this, and it won't be cheaper, so what is the marginal benefit?

Looks pretty, and Al is "race car stuff"

Don't mean to piss in your coffee, but some materials are just not correct for certain applications.

It's all about what people want, and not everyone can see the engineering side of things, weird right!? I agree that Al is not the right choice for someone who really uses their rig, but for most it would be just fine, and after that it all comes down to marketing.


[MENTION=98153]MStudt[/MENTION]Toytec is releasing a full set of Al Upper and lower rear condtrol arms if they havent already. I saw the prototypes at overland expo...

 

[MStudt]

Toytec is releasing a full set of Al Upper and lower rear condtrol arms if they havent already. I saw the prototypes at overland expo...

I saw them as well. I'm pretty sure they're already out, and around $400 a set or so. Many places are selling these now, and people have been running 7075 links longer than Toytec has been in business. The 7075 links are pretty big in the Ultra 4 world, and those guys beat the sh*t out of them. I ran 2-1/2" links on my YJ that were close to 40" long with no issues.

 

[D Farms]

you could just weld the aluminum right onto the steel using a fig welder.

 

[legokcen]

you could just weld the aluminum right onto the steel using a fig welder.

 

[D Farms]

fig: facetious inert gas welding.

 

[RussToy]

I'm playing around with the idea of making some 7075 aluminum LCA's that are adjustable on both ends. Is this something that you guys would be interested in? They would be 1-3/4" OD, and drilled and tapped with LH & RH threads. Pricing maybe around the $400 mark.

Ok...so there's a 5lbs different in weight between Al and steel..what's the difference in cost?

And then any idea what the UCA and panhard in Al is going to cost?? Again what do they run in steel?

How will these hold up in the winter driving with all the salt? I know some of yall don't have to worry about this issue (I hate yall..lol!!). But us folks in the North East...this should be one of the first question we ask.

Just trying to see what...if any...are the benefits for going with Al instead of steel. Well, I mean...besides the "Cool" factor of having Al "race parts"...haha!!

Thank you Sir...

- Russel

 

[IBallEngineer]

My counter-arguments above, I won't buy anything but think aluminum stuff looks cool and it can easily be designed and engineered to be stronger than the stock links.

Also funny enough I was finishing putting together some new beadlocks yesterday which are aluminum but have grade 8 fasteners and the instructions say NOTHING about anti seize and that you should replace the fastners if they are ever removed. But it doesn't take a genius to know that the aluminum will fail long before the grade 8 ever will and you could easily run stainless fastners or a lesser strength bolt, and obviously whoever designed those wheels didn't account for the galvanic corrosion between the steel fastners and aluminum wheel. I went and put anti seize over everything and then modified their torque spec to suit the lubrication. So yes, some companies run steel into aluminum but on the flip side they don't seem to do any engineering--just like 99.9% of the companies in the offroad segment.

Boy do I ever agree with you about 99% of the crap that get's put out as a "kit". Still just because all those dummies are doing it, doesn't mean it is acceptable.

Aluminum has it's place, I don't believe I'd use it for threaded links on an offroad "crawler" type vehicle. CroMoly is light and strong, works for me.

I believe we could argue the pros and cons all day and make good arguments for both. Still I've seen too many issues with dissimilar metals to make me use aluminum for such an application. But I have no doubt it could be done.

Could you build it and test it for a few years then get back to us? heh

:rockon:

 

[MStudt]

Boy do I ever agree with you about 99% of the crap that get's put out as a "kit". Still just because all those dummies are doing it, doesn't mean it is acceptable.

Aluminum has it's place, I don't believe I'd use it for threaded links on an offroad "crawler" type vehicle. CroMoly is light and strong, works for me.

I believe we could argue the pros and cons all day and make good arguments for both. Still I've seen too many issues with dissimilar metals to make me use aluminum for such an application. But I have no doubt it could be done.

Could you build it and test it for a few years then get back to us? heh

:rockon:

I've tested it for 4+ years on a YJ that I beat the sh*t out of. Does that count? It saw more abuse in a year than my 4runner will see in a lifetime.

It was just an idea. Don't think I'll actually do it since Id need to upgrade to a lathe that has a 1-3/4 center bore. I don't feel like spending that much on a USED lathe. I could buy a car with the cost of a new one.

 

[IBallEngineer]

I've tested it for 4+ years on a YJ that I beat the sh*t out of. Does that count? It saw more abuse in a year than my 4runner will see in a lifetime.

It was just an idea. Don't think I'll actually do it since Id need to upgrade to a lathe that has a 1-3/4 center bore. I don't feel like spending that much on a USED lathe. I could buy a car with the cost of a new one.

Nope YJ's don't count, they're like Canadians!

That would be a big lathe, how big is your lathe now? I want a lathe, and a mill, no I NEED a lathe. :fishing: