Replacing Steel Components with Aluminium Alloys: A Simple Density Question

[ilyas415]

Homework Statement

The problem is: "Aluminium alloys have a density of 2385 kg m^-3 and steel has a density of 7015 kg m^-3. If aluminium alloys are used to directly replace steel components there should be a three-fold savings in weight. Why cannot this be done?"

Homework Equations

Density = Mass/Volume

The Attempt at a Solution

I decided to work with 1kg of both metals. I took the equation and rearranged to find the volume of both metals if there was 1kg of them. I got a larger volume for the aluminium than i did for the steel.

Does this mean that the answer is that the aluminium alloys would be larger than the steel components so it cannot be done?

Also, I know generally than aluminium is light and strong, but steel is much stronger I guess. Could I mention that the new components might not be able to handle the stress as well as the steel components?

This is a exam question worth 4 marks. Thanks for your help in advance!

 

[cepheid]

If aluminium alloys are used to directly replace steel components

I took this to mean that a new component is made with exactly the same size and shape as the old component, only out of aluminum rather than steel. So I'm not sure much of your remaining discussion about things taking up different volumes is really relevant. In particular, I think the answer to the following question

Does this mean that the answer is that the aluminium alloys would be larger than the steel components so it cannot be done?

is NO, since you're making identical components out of both materials.

Also, I know generally than aluminium is light and strong, but steel is much stronger I guess. Could I mention that the new components might not be able to handle the stress as well as the steel components?

This is the only reason I can think of why a blind substitution of steel components for aluminum ones might not work, but it is application-dependent, and it requires you to use information (about material strength) that is not provided in the problem. So I don't know.