Re: Why aluminum - Strength Is Not The Reason!!!
Strength means generically 'strong' to most people. As an engineer who makes ultra high precision systems and components, 'strength' means nothing to me, I have to know 'strong' how. The how is going to be a function of how the material will be used, the material itself, what form it needs to take, the materials it will be in contact with, how it is processed and how much you want to spend. There's a lot more involved, obviously, but that's a good short list.
Using that list, it is an enormous challenge to find the most suitable material for exotic projects, like a Mars rover. Among the known factors, exotic projects often have significant unknown variables and my job as an engineer is to assess the project and calculate around those unknowns and select what I believe will be the most suitable material that meets all the requirements, not some of or most of, but all of.
Aluminum and its various alloys are often the go to material because it meets those criteria in a huge majority of situations. When you consider the unknowns it is foolish and extremely expensive to use an exotic material that has its own wacky hangups and meet the requirements.
You'd look pretty stupid if you put a rover on Mars and the wheels rusted off 11 hours after it arrived :) There are simply too many unknowns to go introducing more by using expensive exotic materials. Do you want to pay $15k per wheel or $65k per wheel if you can't be sure how the material will act once it gets where it's going.
I'll leave you with this. Here at my shop, we are generally regarded as a (if not the) world leader in the processing and use of titanium and its alloys. It's what most of my patents are built around and although we create things from all manner of materials, titanium is our specialty. It's a wonderful material for some applications, but about 99.7% of the time It's really, really dumb to use titanium. People think Ti is super strong, but it really isn't all that. It's rather lightweight and doesn't oxidize too badly which are its strongpoints, but overall plain old copper is less prone to failing in situations where Ti has been used. If it wasn't for the oxidation problems and weight of copper it would be better than Ti in nearly any application.
In closing, 'strength' in a material is defined as how appropriate the material is for its task. That makes something strong, not how hard it is to bend or break.