Martian

"I do not believe this would have happened to steel!"
"That's why going to aluminum was a bad idea!"
"They're both the same, quit complaining!"

It's finally here!

What with all the hubbub about steel this and aluminum that, there was a very painfully obvious vacuum of knowledge. How do we solve this?



If there's a circumstance that is met with a response like the ones above, you come here and ask the questions. This thread shall serve as an actual knowledge base and consulting thread with an expert in the subject.

Et maintenant, sans plus attendre, je vous présente mon ami @MrMeeseeks.
(And now, without further ado, I present to you my friend...)

MrMeeseeks

Thanks for that fine intro, Martian!

If you were to Google the material properties of raw aluminum and of steel, then yes, steel is stronger than aluminum [by weight].

But! The exciting thing about modern vehicles is they're made of an aluminum alloy, in the case of the F150s - the 6000 series I believe. Likely 6061.

Anyway, back to strength. When designing with steel you're limited by its yield strength. The good thing about this is it has larger "plastic range" between its yield strength and ultimate strength. In other words, its ability to bend without breaking so to speak. So when your crazy ex throws a rock at your truck it just dents instead of blowing through it like a cannon.

Designing with aluminum you're limited to the rigidity. So if you're going to design an aluminum body to the same standards as a steel body, this will force an over higher yield and tensile strength. The alloy is specifically made to be higher in overall strength. For the 6000 series alloy this means combining with some other materials, being heat-treated, etc.

So lets say we have our aluminum alloy now, whose strength is at least the same as it's steel counterpart per square inch. Only now you can build the body thicker and still come in weighing less than the steel (yay for fuel economy). Because of the added material your aluminum body is stronger than your steel body, made to the same standards.

Now the aluminum will better resist distortion (dent) from real-world occurrences like ...your crazy ex throwing a rock at it. So while, yes, steel is stronger than [raw] aluminum generally speaking the aluminum body will be overall more efficient structurally. (When considering, strength, weight, size, etc)

So aluminum alloy is better? Not necessarily. Steel is super resistant to abrasions. This is a huge advantage for steel in practical applications. Being heavier can give it an advantage in terms of comfort. We know it's certainly more ductile than aluminum. That "plastic range" can really come in handy.

TL;DR: It really depends what criteria you're examining

SCORGE

So...what is your overall opinion on the automotive industries' migration to aluminum bodies/components in vehicles?
Also, do you think that frames may eventually be constructed of aluminum as well? Or would that be something to keep steel.

MrMeeseeks

Overall I think the decision makes a lot of sense, especially financially, in the long run. And of course anything getting better fuel economy will keep the EPA off your *** for a while.

Steel bodies are great. I'm not knocking them. But we do have to consider new changes and the companies (I.e. Ford) don't do that ***** nilly. There is a lot of research and calculating that goes into making sure the changes can meet or exceed the same design requirements.

Every product eventually evolves and sometimes has kinks to be worked out but I think this is step in the right direction.

As far as frames...I think with the lower modulus of elasticity in aluminum they'd have to be considerably larger or at least reinforced with steel right now. There may come a point where it makes more sense to make them aluminum, and there are certain vehicles with aluminum/reinforced steel frames now, but right now steel is cheaper to source, fabricate, and can be made more compact.

Also you'd really have to consider the strength of the welds since the frame is made to support the entire weight of the vehicle. Aluminum strong enough to do that kind of work, maybe 7000 series alloy, would be very expensive.

Aluminum also has a lower fatigue strength so vibrations (and pot holes) will have a bigger impact and may lower the service life. I haven't done much research on that specifically myself but I imagine that is a factor so again, it depends what job you're looking for it to do to know which would be the better option.

SCORGE

On the whole, is aluminum cheaper and easier to create with, versus steel?

MrMeeseeks

Aluminum is actually more expensive to source and fabricate than steel [by weight]. It CAN be more expensive to work on if the shop isn't equipped with the proper tools and is used to working with only steel. With the proper tooling and an experienced shop the cost of fabricating aluminum isn't much more than steel.

The reason I say it makes more sense financially in the long run is that the aluminum should last longer, have better fuel economy due to the weight, and give the vehicle a better resale value.

SCORGE

Here's another question. Can having more parts on a vehicle made of aluminum, positively or adversely affect ride quality?

MrMeeseeks

Well what exactly do you mean by ride quality? Distance, smoothness?

SCORGE

The smoothness of the overall ride.

MrMeeseeks

I would guess that has more to do with the quality of your tires and suspension, and the balancing, rather than the material the components are made up of.

ETA: So if I didn't directly answer your question, I don't think it'd have a noticeable affect on ride quality either way.