Steel Vs Aluminum in the FT86
 

Ive been reading up on aluminum being used in place of steel and am aware there is a torsional difference between the two, with steel being much stronger at the cost of weight. So, in your preference, which frame would you prefer, aluminum or steel? Are there any confirmations on which one the FT86 will have? Also, what are the upsides and downsides of using each in body panels, suspension, wheels etc?

Im no expert on metals - i barely scraped though Chemistry with a pass...

But i've used 6082 Billet Aluminium on lots of auto related things in the past and its a VERY strong metal.

I'd be perfectly happy for the FT86 to be entirely made out of Aluminium.

But i doubt much of it will be as it really drives up the production costs of the car.

Would be nice to see things like the bonnet/roof being Aluminium though. Being the two biggest flat sheets of metal on the car it would help keep the centre of gravity as low as possible and keep the weight of the car down.

I used to have an Audi TT and I think they used both steel and aluminium and positioned the heavier steel to balance out the weight of the car. Maybe they might do that with the FT-86 ?

It's more likely that they use high-tensile strength steel to keep the weight down, which tends to be more economical. Not all steel is created equal, and you can keep weight down depending on the steel used.

How much lighter is it? Does it come close to aluminum?

Not many cars iv heard of that use a Aluminum frame...actually i cant think of any off the top of my head other than a few Corvettes.

Advanced High-tensile strength steel (AHSS) keeps evolving, but it's something like 10-15% heavier than aluminum I think? But you're also able to keep things more compact with AHSS compared to aluminum, which is why it's used a lot in areas like the A, B and C-pillars in cars. Aluminum is also about 50% more expensive than high-tensile strength steel.

^ especially when it contains certain levels of carbon

Both Lotus and Aston Martin use extruded and bonded aluminum. In the Lotus the aluminum extrusions create a chassis "tub", and in the Aston Martin's the extrusions are assembled to create their "vertical/horizontal" superstructure. The Corvette Z06 and ZR1 use hydroformed aluminum chassis rails, however base Corvettes and Grand Sports use hydroformed steel chassis rails.

If you want to start talking about aluminum unibodies, then Audi has been doing that for many years in their A8.


Regarding the FT-86, it's price point is simply too low to be able to afford aluminum in any significant quantity. Perhaps an aluminum hood and/or decklid, but the main structure will almost certainly have to be steel/HSS panels formed into a unibody to fit the price-point.

Is the FT86 likely to be heavier than the Audi TT ?
The TT body is 69% aluminium and the whole car weighs 1260kg.

Aluminum only makes cars expensive to fix. Definitely not suitable for a budget-minded car like the FT-86.The TT is likely not any lighter because of AWD.

The TT here weighs 1470kg (3241 lbs). I imagine the FR will be closer to the number you posted above but we'll have to wait and see.

It's not a fair comparison, regardless of the materials used. The TT, being both Audi and German, means it's over-designed and generally over-weight. You'd be hard pressed to find a current German production car that resembles light-weight. Japanese cars are generally more svelte, delicate, and smaller. The FT-86 is a small car, barely larger than a Miata.

A Bugatti Veyron is built using a carbon-fiber chassis tub with titanium fasteners, yet weighs a scathing 1,888kg. A Mazda Miata uses a steel unibody and weighs 1095kg. Even though they're both small 2-seaters it's not a fair comparison.

The whole package needs to be considered. Size, strength, powertrain, luxury accoutrements, everything.

i doubt there will be much aluminum do to the scion price point. bmw //M suspension components are all aluminum and audi uses aluminum space frames to save weight but these drive up the cost. i think they can get away w/o using aluminum by just dropping the luxury features. heavy luxury seats and big engines/drivetrains (ie awd) are the source of most of the weight in new cars.

I think the TT and FT86 will both be chasing the same buyers (in the UK at least). They're both 4 seat coupes and about the same size. FT86 might be a little bit cheaper though.


I forgot about the quattro though, that adds another 100kg and brings the weight of the TT up to 1360kg (2.0 TFSI).

In the USA, I can't imagine cross-shopping a TT to an FT-86. It'd be like comparing a MB S-Class to a Porsche Cayman.

Well, I had my eye on this little TT at my local Audi dealer, but I might just forget it and wait for the FT86:-


http://i194.photobucket.com/albums/z...ine800x600.jpg

Ughk. TT = not serious about handling. They're also way too big and heavy for my money. Go pick up a copy of the latest EVO and read "The Knowledge" and they'll point you in the right direction for a coupe', if that's what you want. For TTS money you can get an Evora or 370Z, something that actually handles good.

I think the FT86 will struggle to better the 1260kg weight of the TT because of its 69% aluminium body.

The main "problem" is, the TT is FWD.

The TT does not weigh that little here in the USA. The base TT coupe starts at 1470kg. Like I said, German cars are inherently overweight.

correction. TT can be FWD. They do make Quatro

hah. Tell that to the Cayman R

Is that the 3.2 V6 ?

Here's the weights for all current variants:-

No, it's right there on AudiUSA's website; 2.0T 211HP quattro coupe = 1470kg

The Cayman R is overweight. 2855 lbs is light for a Cayman, but that makes it 0.44 Tons heavier than my Exige, and I still have A/C, a stereo, and actual interior door handles. There, I told it. :bellyroll:

The Cayman is also longer and slightly taller than the FT-86 will be, all while having a shorter wheelbase. Not to mention the price and luxury level are slightly different, making it a perfect sports car for well-heeled people not crazy enough to be fun but still want to prove they're worth being part of society. It's a great all-a-rounder, in other words.

:suicide: what are you talking about man? Its one of porches most capable platforms.

You're right. That means it's still slightly more boring than it needs to be. It handles great, has great steering feel, and is almost fun.

When I get old and decrepit, I'll likely want one.

What kind of weight figure would you figure the FT86 could have then, if they used AHSS? Would it be lower or higher if they use aluminum, accounting for all the additional thickness needed for torsional rigidity?

I think it's hard to say, there are many many different alloys.

Common aerospace usage aluminum is 7075 or 7068, which have yield strengths around 80-90 kpsi. Some steel alloys can be up 350kpsi yield strength. Thus it appears steel can have a higher yield strength/density than the strongest commercially produced aluminum. Of course yield strength isn't the only thing that matters, but you can see that it could really go either way, depending on other properties or specific alloy.

:dnftt:

Time to clear up some metallurgy here people.

There is NO way any form of steel is going to weigh only 15% more than aluminum.

Steel's density is approximately 490 lbs/cu ft.
Aluminum's density is approx. 170 lbs/cu ft.

The alloying elements in the metals are usually tiny compared to the amounts of base metal so there are only very minor differences in the weights of all steels or all aluminums. This is more for carbon steel and alloy steel as opposed to high-alloy steel, and tool steel which use a lot more alloying elements, and cost a lot more dollars.

Carbon is for steel, it has no place in aluminum. The high strength aluminums alloying elements are copper for 2000-series, magnesium/silicon for 6000-series and magnesium/copper/zinc for 7000-series.

The kick-ass aluminum alloy is 7075, in T6 heat-treatment condition (precipitation hardened and artificially aged).

6061-T6 is the 'workhorse' alloy in fabrication and machining and the one I use at work all the time.

Comparing 6061-T6 to mild steel for component weight, compare the aluminum's tensile strength of approx. 45000 psi to mild steel's approx. 60000 psi. So the aluminum would need about 50% more cross-sectional area for the same strength. Then compare the density of aluminum at 170 lbs/cu ft to steel's 490 lbs/cu ft. Now you can get an idea of where the aluminum gains in the strength to weight area.

The almost magical 7075-T6 tensile strength of 83000 psi to 4140 chrome-moly's 95000 to 125000 (varies by hardness) psi, and with the same densities as above.

Now the drawbacks is that these aluminums are not suitable to all forms of manufacturing processes.

As someone said, steels are typically way cheaper, and also easier to work with in certain processes. For example it is impossible to weld 7075 aluminum and have it maintain it's T6 heat treat level, so it loses massive amounts of strength.

And as for chassis application, no one mentioned the NSX???

If the hood and foot were aluminum, how much more would it really cost for a car like the ft-86?

For comparison the 370Z has a ton of aluminum bits (suspension control arms, front sub-frame, calipers, hood, doors, hatch). It also has a carbon driveshaft from the factory.

(source: http://www.nissan.ca/vehicles/common...370z/coupe/en/ )

I'm kind of hoping that the FT86 meets its weight target without all that, so there is a chance to take more out of it tuning it.

That's interesting, I thought the Z would weigh less with all that aluminum. The car still has great bang for the buck, but I wonder how much cheaper it could have been with steel counterparts.

LOL yeah but the Miata would probably fly apart at 200+ MPH.

From what I read on wiki, he NSX saved 200KG by switching to an aluminum frame alone. To me, that's worth the extra cost.

Considering what that kind of weight loss could do for a car like this, it seems it comes down to affordability vs weight loss. Would you pay 5K extra for a car that's about 125KG lighter?

OFFTOPIC: "The boot of the FT-86 will open more like the boot of a traditional saloon/sedan car. However, the final design has not yet been confirmed, further details will be revealed when the final production model is revealed later this year." -Damian Pang of Toyota UK
http://blog.toyota.co.uk/toyota-reve...-86-sports-car
Didnt want to start a new thread.

Considering my long term plans with this car from once I purchase it new, between 3K and 5K extra would be worth it for the high quality advancement.

Keeping that many pounds off the total is hardly easy/cheap.

lol, Dimman I was going to write basically all that but I thought it would be self evident :/
The only aluminum alloys that would make sense for using in a car frame would be 7xxx series IMO. Any others aren't strong enough compared to high strength steel. 6061-T6 has yield strength in the 30s kpsi, while high strength steels are well over 100kpsi yield strength.
Mild steel is pretty weak, but it's cheap and easy to machine, weld, etc. I think they don't really use that much in the automobile industry anymore, so it's not really fair to compare?

Oh and 7068 is stronger than 7075.

It's strength to weight though. Not just ultimate tensile and yield. Look at aluminum mountain bike frames compared to chrome-moly ones. Tubes on the aluminum ones are bigger, but the bikes are still light. Gives a rigidity benefit too, I believe.

I've never really heard of 7000-series in sheet form to press/stamp parts out of. 2024 is used for aircraft skin and has tensile and yield strengths of 68/47 kpsi sounds like a better option.

The 7068 I just heard about recently. Is it a new Alcoa proprietary alloy? I read an article on someone promoting it to replace 7075, stronger and better corrosion resistance. But that doesn't sound cheaper...

I have yet to work with 7000 series, just 6061-T6 every fricken day... but have had some play time with Ti-6Al-4V. :) mmm... white sparky awesomeness...

(The 'self evident' stuff was to clear up some of the less than clear talk earlier in the thread. Especially the steel being 15% heavier. No way. Maybe the equal strength finished part, but not the metal itself.)

Yeah...couldn't help it....the nerd in me took over.

http://www.youtube.com/watch?v=a_DdHi5cfY4

Best one I could find.

Edit:...it wouldn't embed, QQ

Right that's what I mean. 6061 is less than 3 times as strong as many high strength steel alloys, while weighing 2.5 times less. See the problem? :) Of course yield strength isn't the only parameter that matters, and the method of bonding is also important, but you see what I'm getting at.

It looks like 7068 is pretty similar to 7075, mostly the same alloying elements in similar proportions (although slightly different). Interestingly it has a higher copper content (which probably contributes to the strength increase), but that usually decreases corrosion resistance. Metallurgy is some crazy stuff.