: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.

But with design, and thinking about cross-sectional area where the loads are, it's not exactly the same thing as saying, "Well it's half as strong, so double the size." It's a squared-cubed thing, and we're dealing with density.

I think 6061-T6 compares very favourably to 4140 Chrome-moly in a strength to weight situation. (I'll have to double check...) Plus the rigidity thing of having fatter components can be a plus.

The steel in car bodies/chassis isn't going to be anything fancy, it will be a very cost-effective low alloy type steel. Maybe as strong as a medium carbon steel, but with better corrosion and manufacturing properties. Not going to be a sheet body stamped out of 9840 Nickel-Chrome-Moly, as awesome as that would be...

From my short experience in an auto plant working mainly with the body shop (not for car's coming off the line, but for the part's division), I'd say Aluminum hood and trunk lid are the best bets. Doors,...maybe, at the suggested price range at least.

If you have experience with Toyota sport's cars, then you'd LOVE the idea of aluminum doors...door hinges across the toyota globe would rejoice.

I'd take 2 aluminum doors over 1 hood and 1 trunk lid, anyday.