Next up should be titanium: http://www.defensenews.com/article/20110720/DEFSECT04/107200...
In other words, the British spelling was just a matter of British cultural hegemony at the time, just as American spellings are matters of American cultural hegemony today.
http://www.worldwidewords.org/articles/aluminium.htm
I didn't know any of this until just now.
"Sir Humphry made a bit of a mess of naming this new element, at first spelling it alumium (this was in 1807) then changing it to aluminum, and finally settling on aluminium in 1812."
To me it reads that British academics (Sir Humphry's peers) prefered the -ium spelling. It doesn't say they used political pressure to force him to change it.
While the use of both spellings were in almost equal use in the general British and US populations for a long time, the article hypothesises that the -um spelling became dominant in the US because of Webster's -um entry.
Steel is easy to weld (depends on type, but generally) Aluminum is harder Titanium is even harder. It reacts with nitrogen.
Steel is relatively easy to machine Aluminum can be even easier. Titanium is very hard.
Sounds like there might be some roadblocks on wide spread adoption of titanium still, even if the raw material gets cheaper.
The SR-71 was largely constructed out of titanium since the whole airframe heated up to high temperatures in high speed flight. The maintenance facilities had welding stations that had nitrogenless atmospheres under a "bubble".
Mechanical engineer here. This depends heavily on the alloy you're dealing with. Many Aluminum alloys are so soft that they'll actually melt and subsequently bond to the tool surface when they're being cut/ground/sanded/etc.
Also Aluminum tends to have a very low shear strength which means it won't hold a thread the way most steels will - this is why you typically see rivets in aircraft skin.