Let me rephrase the above, most aluminum alloys are stiffer than mild (pure) steel. There are some very stiff steel alloys as well, it's all in the alloy.
The reason aluminum is “stiffer” than steel in an application is all about thickness, not material properties.
Al is about 40% of the density of steel. This means that, for a given weight, you can make a part 2.5 times as thick with aluminum than steel.
The resistance to flex (stiffness) of a substance is proportional to a power (the cube?) of the thickness.
The thicker Al, while not necessarily any stronger than a good steel alloy, is much stiffer due to the thickness of the material.
A good example of the above is the new F150 using Al body panels. Since the limiting factor here is resistance to flex/denting, not ultimate strength, Al is better than steel, which would be too “noodly” at an equal weight. You “could” make steel to do the same thing, but it’d have to be honeycombed or some similar structure with internal voids.
@keith, aluminum is not stiffer than steel. If you make a spring from steel it will always be stiffer than the identical dimension of aluminum. The Modulus of Elasticity (also called Youngs Modulus), essentially the non-dimensionalized spring rate, is lower for every grade of aluminum than every grade of steel. Al is about 69 GPa and steel is about 200 GPa.
This is not to be confused with hardness, ductility or yield strength which you correctly stated vary quite a bit according to grades and heat treat for both steel and aluminum.
meanjoe75fan, isn’t the higher performance (better handling?) you mention due to the typically wider and lower profile tires that accompany most wheel upgrades? The point I have yet to see definitively answered is whether steel or aluminum is better for wheels of the same size. Thanks to the many comments here, I’ve learned that the construction of the aluminum wheels (e.g., cast vs. extruded, etc.) can also have an effect. Even the Car & Driver test I linked to above is with different size wheels, and it’s not a “blind” study.
This discussion makes me recall my first sports car, a brand new 1957 TR3. It had steel wheels. A friend bought a 1958 with wire wheels and used to brag about his “better” wire wheels. Well, he spent a lot of money to have them trued and balanced. That evening we were driving faster than we should have been (we were 18). He slid a bit around a corner and ran into a curb. Just a minor bump, but it sure screwed up his wheels. In the same situation, my steel wheels might have gotten scratched a bit. Wire wheels are a real pain.
What!!! Did @WESW; call me saying my icecream is ready!!!
I’m no expert on Steel alloys…just the few that I prefer to use for tool making.
But sorry, Wesw I have to disagree with you about making a piece if mild steel brittle enough to shatter. Just not enough carbon in it for that.
AS far as Aluminum goes I know little except that there are alloys in aluminum too. The aluminum in those racks at the hardware store are a very soft purer form of aluminum and could never be used to make anything that has to be rigid. Far too soft.
I’m not sure what the alloy is that we buy from the supply house for shoes…there is only one choice for us. All I know is that it takes more to shape this alloy than the hardware store stuff.
And when we forge it into shoes…we keep a piece of newspaper on hand. When the aluminum is hot enough to forge it will char the paper, if it doesn’t put it back in the fire.
Our Farriers Organization once held a clinic with a world renowned farrier from England. We knew he would want to make an aluminum shoe as part of the demonstration, so the one in charge got some kind of aluminum alloy that just would not forge. He heat it and as soon as he hit it with a light hammer blow it just crumbled into chunks that fell to the floor. THe poor guy figured something was up after the third try.
Because Aluminum shows no color changes while heating it is easy to vanish before your eyes.
Too hot and you’ll pull 1/2 a shoe out of the fire. Where it went is a mystery…you clean the forge and it’s not there. Magic!!!
Have I ever melted a steel shoe in half…you bet…a few times, I was too busy telling a story and turned to see fireworks in the forge…ooooops!!!
At least I find it in the bottom of the forge as a clump of steel and slag.
Here’s a puzzler for you. He made a copper shoe and said that it was still widely used in Britain yet. Why would you ever want to put such a soft metal shoe on a horse???
well, ok crack, once i crystalize that sucker with the torch it ll crack on its own as it cools.
i ve spent countless hours cambering beams with heat that were too big for our camber machine.
you have to do it right tho, too much heat and it will crystallize and be subject to cracking.
it can take all night to put a 3 inch camber on a W36x300andsomething x 50’long beam.
i worked on huge steel members for 20 yrs. all facets of fabrication. we mostly did govt work. universities, air traffic control towers, military bases, museums, courthouses and the like.
the changes in fabrication and design after 911 were profound. they were designed to be blast resistant and the members were huge. some individual members made the 10 ton crane groan.
mild a36 steel is not really used for main members anymore, its all dual use a992 grade now. that replaced the v50 steel and a36 steel that was previously used. most of the parts are still a36
@meanjoe75fan
Is absolutely right. I have worked with corresponding parts in marine applications made from steel, stainless steel and cast aluminum. You really must take into account the general design plus the construction material and not just the material itself before you can make general statements about which is best. There are times for example, that the mounting bracket or Gudgeon for a rudder for example is better served by a stout cast aluminum piece then a fabrication in steel or stainless less steel as far as strength is concerned…and the same goes for wheels. Heck, there are times when plastic is better then a too thin piece of steel.
The lighter un sprung weight of alloy has the potential for a better ride and handling given the same rim size diameter and rim width . I don’ think though, cargo weight savings is as big a concern.
Ah, music to my ears.
Let,me spill a bit about truck beds for back dumps,the Boss one day commented on the fact that sometimes the Aluminum beds werent that much lighter then the steel “contractor” beds,simply because they had to be made thicker.due to the wear rates when hauling abrasive materials.
So different,materials for different apps,I’ve noticed the “Pursuit” rated state vehicles have steel rims and high speed tires-Kevin
@Kmccune; gave the perfect example to simplify the topic. Quote; “Aluminum beds werent that much lighter then the steel “contractor” beds,simply because they had to be made thicker.due to the wear rates when hauling abrasive materials.”
It all depends on the wear for the application, and strength needed for the part itself and it’s associated parts. What torque is going to put on the part along with load and shear pressure.
A steel wheel might be made of only 1/8 inch steel, but the aluminum one must be 3/8 thick to carry the same load. Granted the aluminum is still lighter.
Here's a puzzler for you. He made a copper shoe and said that it was still widely used in Britain yet. Why would you ever want to put such a soft metal shoe on a horse????
@Yosemite
Would you want a soft shoe to create less wear on certain roads?
Copper has antimicrobial properties, so it helps prevent bacterial and fungal infections. Hmm, I wonder if the penny loafers of my youth helped prevent athlete’s foot?
yes. aluminium can be pure, its an element. steel is a compound, not pure. it contains iron and carbon which are pure as they are also elements.
Rust is a compound, (iron oxide), steel is an alloy. Elements can contain impurities, compounds can be quite pure. No matter how pure you make water, it’s still a compound. No matter how many impurities a cylinder of hydrogen contains, it’s still an element.
asemaster I don’t remember when I learned an Impala was an antelope. It could have been as a little kid from reading lots of animal books or when I was around 12 and reading safari stories in gun magazines. As a teenager I read Hot Rod, Car and Driver, and Road & Track. I started working on cars when I was around 16 and stopped when I was around 30. Once EFI, computers, modules, and all the EPA stuff became common. At that point I suppose the motor oil started draining out of my veins. I guess I would call myself a “functionally” retired gearhead. Although I’m no longer hands on I still have a huge interest in everything automotive related. On May 25th I was up before dawn so I could watch the Monaco Gran Prix, Indianapolis 500, and Charlotte Cup 600! I have owned 2 Impalas. A 1960 hard top 348/330 tri-power 3 speed manual and a 1963 convertible SS 327/300 4 speed. I just thought it was hilarious that da boyz in da hood called Impalas Donks because of their badges. Of course they have probably never seen a donkey or an impala antelope so I can understand their confusion. Not really.