Chevy Pokes Fun at Ford Aluminum Truck

jwstewar · Jul 12, 2015

I have a buddy that fixes cars and resales them. He had a Caddi a while back in that he was working on. It originally came with an Aluminum hood. He priced a new aluminum hood, it was almost $900, a new still hood was a little under $200, both were aftermarket.

Copperhead · Jul 12, 2015

MossRoad said:
Aluminum hoods is one thing. Aluminum in the wheel wells is quite different. I wonder how it will hold up to rock chips and salt, road grime, etc... we'll find out in a few years one way or the other.

Well, that is why there are things called wheel well liners. Let's look at this at a different angle. The hood and fender wells on the front of my semi truck is fiberglass. You would think rocks would pretty well beat that up, especially since I run the truck down gravel roads a couple of times a week. But no, the wheel well liners protect it. Salt and road grime has less of an effect on aluminum than steel.

The auto and pickup OEM's are actually a little late to the party. Except for the hood on my semi truck which is fiberglass, the entire rest of the body is aluminum. The wheels are aluminum. The exposed side fuel tanks are aluminum. All the frame attached boxes are aluminum. Even the 5th wheel that has to pull a 53' long, 102" width trailer (aluminum plate trailer, all aluminum except axles) that has to haul 46,000+ regularly, is aluminum. Yep, Alcoa aluminum 5th wheel. The frame is steel, but I could have opted for an aluminum frame also. Price caused me to balk. Even the twin rear drive axles are aluminum housing Meritor 14x axles. One is going to have to explain why it is a semi truck primarily built of aluminum has no problem running 10-20 years in the rust belt, to the tune of 120,000+ miles a year, in rain, snow, salt and calcium chloride, and is not falling all apart.

Not quite sure why an aluminum pickup causes some to cringe. And it is pretty lame of GM to poke fun at it. Just because they don't have the candle power to do it themselves. Oh, in the spirit of full disclosure, I own a 2015 2500 Silverado, so I have standing to take all the shots I want at GM I wish.

And aluminum can't stand up as well as steel? Well the typical box van semi trailer, there is NO frame underneath! That's right! No frame except a couple of rails where the axles slide on. There are cross members under the floor, but the entire load and structural integrity of the tailer is done by the walls of the trailer. And plate trailers like I use, the walls are .5" thick aluminum panels riveted together. The cross members under the wood floor are aluminum, and again, riveted to the aluminum rail that attaches to the aluminum side wall panels. And I have no problem loading up ten 4500 lb steel coils for a customer, including the heavy forklift that is running in and out of the trailer loading them.

Egon · Jul 12, 2015

It's all about design and weight.

s219 · Jul 12, 2015

Copperhead said:
And aluminum can't stand up as well as steel? Well the typical box van semi trailer, there is NO frame underneath! That's right! No frame except a couple of rails where the axles slide on. There are cross members under the floor, but the entire load and structural integrity of the tailer is done by the walls of the trailer.

That's a perfect example of the "system" level analysis needed to evaluate a design, which goes way beyond the material. Heck, in the space world they have advanced to inflatable structures, where air pressure inside a bladder deals with loads. And think about strip-built canoes made from cedar and balsa. Any material can be made into a strong structure with smart design.

aczlan · Jul 12, 2015

s219 said:
Any material can be made into a strong structure with smart design.

I have seen a 2' long balsa wood truss hold a 5 gallon bucket full of sand and 3 truck ball mounts (all suspended from the center) before it broke.

It was quite impressive.

Aaron Z

Redneck in training · Jul 12, 2015

s219 said:
That's a perfect example of the "system" level analysis needed to evaluate a design, which goes way beyond the material. Heck, in the space world they have advanced to inflatable structures, where air pressure inside a bladder deals with loads. And think about strip-built canoes made from cedar and balsa. Any material can be made into a strong structure with smart design.

Blades of industrial size wind turbines are made out of balsa covered by composite.

dragoneggs · Jul 12, 2015

Brad_Blazer said:
I guess you are trying to say that steel has a higher modulus of elasticity (E) than aluminum. True but I'm pretty sure they increase the thickness of the aluminum to match the tensile stiffness (EA) of steel (thickness inversely proportional to modulus). The bending stiffness (EI) of the aluminum panel will then be greater than the bending stiffness of the steel panel due to cube function you mention when calculating moment of inertia (I).

Edit, I looked up some numbers and the weight will stay about the same if you match tensile stiffness. Steel modulus and density are both about 3x that of aluminum. An aluminum panel as I described above would be the same weight as a steel panel but 3x as stiff in bending. They must be shooting for something in the middle if they are saving weight.

Of course they could be shooting for a yield strength value which becomes much more complicated as yield strength of both materials can vary widely based on alloy and temper.

It is generally the bending stiffness rather than tensile (axial stiffness) that drives the design of sheet metal in cars. Other axial loading failure modes can come into play such as buckling or crippling but for the simple matter of aluminum vs. steel and bending stiffness, it is definitely not a push on weight.

As Larry pointed out, bending stiffness is most affected by the section moment of inertia (cube function of thickness). So... as an example a 1in wide by 3in tall section will be 27 times stiffer than a 1in by 1in section (same material). Now make the 1in by 3in section aluminum, and the 1in by 1in section steel. They are the same weight but the aluminum section is 9 times as stiff as the steel (in bending). This is because the modulus of elasticity of steel is three times that of aluminum. I hope I did my math right on this beautiful Sunday morning!

Therefore potentially there are some real weight gains to be had using aluminum in place of steel. Of course other design concerns can come into play when choosing aluminum vs. steel. Fatigue, corrosion (galvanic due to dissimilar metals), stability (i.e. buckling, crippling) are a few.