CRR-CRRRK, beep, beep: Mars space truck backs out of slippery sand trap Curiosity, our favourite Mars-cruising nuclear truck, has just dusted off its latest potential drilling target, the “Bonanza King” rock. Curiosity brushes potential drill target Bonanza King The rover used its aptly named Dust Removal Tool on its robotic arm to sweep off the red, oxidised dust on the surface of the planet …
Yep, I'm having trouble IDing the alloy, also.
Older rovers (Spirit / Opportunity) appeared to use 6061 in the T6 temper, which is about as generic an aerospace alloy and heat treat condition as you can get. See side bar comment on museum donation here:
http://www.divtool.com/albuquerque/about_us_diversified_tooling_corp.html
According to this thesis (warning: 10MB), Sojurner's wheels were "stainless steel" (alloy not specified).
http://c3p0.ou.edu/IRL/Theses/Mills-MS.pdf
I'd be willing to bet that Curiosity's aluminum wheels are 6061-T6 or a close cousin. It remains tough (fracture resistant) and strong at low temperatures. It's light for its strength. It is corrosion-resistant (especially with anodizing), moreso than other aluminum alloys in the same strength range (like members of the 2000- and 7000-series) and Mars does have all those interesting superoxides that designers might worry about. It is proven in this application (on Spirit and Opportunity). The amount of knowledge in the aerospace community on handling and working 6061 is immense. (At my office it is a small challenge to get mechanical and aerospace engineers to select something else, even when there are more appropriate materials.)
I would've been certain the wheels were 6061-T6 is Sojourner had also used the material, but the change between Sojourner and Spirit/Opportunity means the engineers aren't as strictly of the "if it ain't broke, don't fix it" as I expected.
For the future, I'd go with steel, probably a stainless steel. Something like 13-8 Mo. It remains decently elastic in Mars' temperature ranges, is corrosion resistant (if that matters), is quite strong, quite tough (though in the medium-strength H1000 condition it starts bottoming out in Martian winter+night conditions - the H1150 condition might be better if that's a concern), and quite hard (Rockwell C 43 in H1000 condition) and wear resistant. It's well known to the aerospace community, which machines it into complicated shapes. Yes, there's a weight penalty compared to aluminum.
No, I wouldn't pick a titanium alloy. I'd want something that's strong, tough, and wear resistant. Despite titanium's fantastic Hollywood PR machine, real titanium alloys don't compare with high-end steels on those counts.
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