Saturday beers with the boys has bought up yet another topic. What is stronger pound for pound, steel or aluminium? If i had 100kg plate of steel and 100kg plate of alumimum what would be stronger.

Mate 1 said: Aluminum is lighter therefore the 100kg plate in question could be thicker and therefore stronger.

Mate 2 said: even if the aluminium is thicker, steel is still stronger aluminum therefore the 100kg plate of steel will be stronger.

Both boys are dumb as dog ____ and i have not a clue although i am leaning towards mate 1s argument.

If steel was stronger pound for pound, I think they would make planes out of it.

What grade of each material is going to be the real determining factor and define strength?

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Hardcarve1 said..
>>> and define strength?

This is the big one! If all you want is compression strength I'd go for steel, because alli is softer, but that's just a guess, could be wrong weight for weight.
Then there's tensile strength + a few others I'm not really familiar with, like shear modulus and stuff like that.
Also temperature range would obviously come into it.
Simple question complex answer, that I'm not on top of.
But as a general rule I like FN's reply.

what sort of steel? low carbon steel? bisalloy? spring steel?

what grade of ally? pure? machine grade? 3003?

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decrepit said..

Hardcarve1 said..
>>> and define strength?

This is the big one! If all you want is compression strength I'd go for steel, because alli is softer, but that's just a guess, could be wrong weight for weight.
Then there's tensile strength + a few others I'm not really familiar with, like shear modulus and stuff like that.
Also temperature range would obviously come into it.
Simple question complex answer, that I'm not on top of.
But as a general rule I like FN's reply.

But a plane uses steel bolts, not thicker alloy ones .

I googled man of steel v aluminum


It appears the aluminum wall was no match

I'm going with Aluminium. To produce a road bike that weighs under 100kg and produces over 100kw they went with a lot of aluminium. I get the feeling these engineers really know what they're doing.

www.wenzelmetalspinning.com/steel-vs-aluminum.html

Steel, as demonstrated in this scientific test

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psychojoe said..
I'm going with Aluminium. To produce a road bike that weighs under 100kg and produces over 100kw they went with a lot of aluminium. I get the feeling these engineers really know what they're doing.

Ducati used to use welded steel tubes and said it was better . A big cast alloy motorcycle frame section is much cheaper to mass produce than welded tube. If not made from composites , racing or drag racing cars are made from welded steel tubes not alloy tubes.
Each metal has it's place.

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psychojoe said..
I'm going with Aluminium. To produce a road bike that weighs under 100kg and produces over 100kw they went with a lot of aluminium. I get the feeling these engineers really know what they're doing.

Ducati used to use welded steel tubes and said it was better . A big cast alloy motorcycle frame section is much cheaper to mass produce than welded tube. If not made from composites , racing or drag racing cars are made from welded steel tubes not alloy tubes.
Each metal has it's place.

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As a metallurgist who studied this topic and many others, including beer drinking, in the great city of Coventry in the UK before seeing the light and coming to WA 50 years ago I'll give you my 2 bobs worth.

There are numerous types and grades of steel so this is data for ordinary mild steel.

Mechanical Properties Tensile Strength, Ultimate440 MPa Yield stress 370 MPa - it will Elongation at 370 MPa and break at 440 KPa and elongate by 15%.




There are numerous grades and types of aluminium alloys. So results for alloy 6061. There is a large range because of the various grades of the alloy and the heat treatment.

Aluminum Temper Designations and Meanings: -F: as fabricated -O: annealed -H: strain hardened -T: thermally treated

It's all a bit confusing so work out your type of aluminium alloy and its heat treatment and then you will get an accurate answer to your question.

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Flatty said..
Saturday beers with the boys has bought up yet another topic. What is stronger pound for pound, steel or aluminium? If i had 100kg plate of steel and 100kg plate of alumimum what would be stronger.

Mate 1 said: Aluminum is lighter therefore the 100kg plate in question could be thicker and therefore stronger.

Mate 2 said: even if the aluminium is thicker, steel is still stronger aluminum therefore the 100kg plate of steel will be stronger.

Both boys are dumb as dog ____ and i have not a clue although i am leaning towards mate 1s argument.

Do many people here remember steel drink cans? I vaguely do and am sure they were a thing.

Maybe ask your buddies why they are drinking out of aluminium cans and not steel ones? Steel's very cheap and cheaper to process I think.

Also, it is often said that people prefer to hang around people of the same intellect

And when we say steel , does that include chromolly and titanium ?
The difference between cast , extruded and forged basic steel is huge.

Transmission lines used to use a steel core for tensile strength and aluminium outer layers for electrical cross-sectional area. Now they use all aluminium using special aluminium alloys to achieve the necessary tensile strength.

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Imax1 said..
And when we say steel , does that include chromolly and titanium ?
The difference between cast , extruded and forged basic steel is huge.

A titanium alloy or titanium (which is not steel)?

I think in the context of Flatty's friends I think they wouldn't be thinking it through too hard.

As a general rule i'd say weight for weight: aluminium. Size for size, definitely steel.

but as others said theres a lot more to it than that. What kind of strength are you looking for? How are you measuring it?

Interesting answers,
Lets say we are talking mild steel and marine grade alloy (5052 or 5083). As we were talking in a boat building context and strength mesured using a bending test (probably not the best test of strength).

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FormulaNova said..
Also, it is often said that people prefer to hang around people of the same intellect

Yeah they are very hands on blokes. They can fix anything but arent what you call booksmart. Usually im the smarter one of the group and believe me im no genius.

Regarding steel cans: i suspect that you dont drink out of steel cans because
1. Steel is very corrosive, unless it has a coating to protect it, it is going to rust
2. They would need to be painted
3. Steel is 2.5 times heavier than alumimium (i think)

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Flatty said.. >>> Regarding steel cans: i suspect that you dont drink out of steel cans because
1. Steel is very corrosive, unless it has a coating to protect it, it is going to rust
2. They would need to be painted
3. Steel is 2.5 times heavier than alumimium (i think)

They aren't called "tin" cans for nothing. It's tin coated steel, and it's still used extensively. just go to the supermarket and look at all the "tin" cans on the shelves. I think you'll only fins alli in the drinks section.

Bending has little to do with strength. A tempered alloy is stiff - won't bend - but will then break suddenly.

SpaceX build their latest rockets from stainless steel.
But they are rocket scientists, so ordinary folks may have different , obviously better ideas.
For those interested in some real life data here is tensile strength
a) the best steel 2800MPa




b) the best aluminium
690Mpa



but if you are looking for something strong , cheap becuse house made spider web silk could do well

I think Elon's smart but stainless steel's high melting point is also a big advantage. *

Typically aluminum or carbon fiber, for a steady-state operating temperature, you're really limited to about 150 degrees Celsius. It's not that high. You can take little, brief excursions above that, maybe 180 degrees C. 200 degrees and you're really pushing it. It weakens. And there are some carbon fibers that can take 400 degrees Fahrenheit, but then you have strength knockdowns. But steel, you can do 820 to 870 degrees C.

Stainless steel is much cheaper than the carbon-fiber material that SpaceX initially aimed to use for Starship and Super Heavy, and the metal has other important advantages as well. For example, stainless steel handles heating far better than carbon composites do and that's crucial for the reusable Starship and Super Heavy, both of which will be making many highly energetic trips through Earth's atmosphere, both up and down.

Carbon fiber costs $135 per kilogram, and 35 percent of the stuff must be scrapped - you cut the fabric, and some of it you can't use. So the true cost of the material is nearly $200 per kg, compared to just $3 for stainless steel...


(* the text above is not mine and I shamelessly stole it from other articles about why SpaceX uses stainless)

The only way for us to get the correct answer here is have an architect with a superior knowledge of engineering to inform us all. Anyone know of such a person ?


Typical structural steel used in "normal" use (i.e. the formed steel sections you buy in the steel shop) is anywhere from 250 to 480 Mpa yield stress. Yes - you can get higher, but pub-talk "normal" steel, grade C or S250 to C450. 20 years ago I'd have said most common, middle of the road was 275Mpa, these days I'd put middle of the range at 350 MPa and density 7850 kg/m3

Aluminum (or aluminum as the Yanks say), equivalent normal, middle of the range material you'd buy from metal shops would be 5005 or 5052 grade, yield strength 85 to 200Mpa, middle of the road I'd say 115Mpa, density 2,680 kg/m3

So steel has "strength" to density ratio of 0.045 Mpa/kg
and aluminum is 0.045 Mpa / kg


Thus I would conclude the choice to use one or the other is not driven by strength to weight so much as all the other properties of the materials.

Main one often being whether it can be melted by jet fuel and/or cut by secret military grade nano-thermite (if required).

On the other hand everything I have just said might be moronic and I might stand corrected. Although not wrong.

A quick google shows steel is 3 times more dense than aluminium 5052. The Youngs modulus of steel is around 3 times that of aluminium, while the tensile strength is around 2 times. Does that mean aluminium wins your comparison?

I used to work supplying container repair parts and dealt with both steel and aluminum.
Corten sheet has so more tensile strength than mild steel but a lot of repairers would use mild steel and charge the higher Corten price.

On a tangent -there was an awesome tool that you could put on unpainted surface and the display would show the material.
I took offcuts of ali sheet 5005 grade, ali extrusion 6061 T6 (what ali windsurf booms are made of), stainless 304 grade as well as Corten and mild steel.

Here's another thought, I think stiffness varies with the square of thickness. So alli should win out here as well

you guys overthink it way too much.

Dragster and BMX : Steel Frames, steel wheels, 40+ years, in the garage
Road bike; Ally frame + rims, 10+ years maybe , in the tip/recyling.

Aluminium alloys are considerably stronger than steel alloys weight for weight but they're not as stiff.

Yeah, but...., nah, but yeah, but ....

....but steel is already an alloy. Whereas aluminum is a pure metal / element.

The question isn't iron vs aluminum - so the answer should based on comparing steel alloy to pure aluminum ??

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Carantoc said..
Yeah, but...., nah, but yeah, but ....

....but steel is already an alloy. Whereas aluminum is a pure metal / element.

Yep, sounds exactly how a drinking time discussion is going to end up.