Seems there was a story going around that in the early days of Reynolds Aluminium, a clerk placed a large order for company stationery, and misspelled the word in question - Aluminum! Because the order was so large, the company decided to let it be and, if questioned, merely assert that this was - yes - the American spelling of the word! "What in the Word?" refutes this notion - here is the real explanation:
However... Wikipedia, interestingly, redirects a search for aluminum to aluminium, thereby inferring a preference for the British spelling. But the article itself seems to take a neutral stance on the topic.
And... Since I have a permanent link to World Wide Words over there on the left, I have to give a nod to its entry for this damnable word.
It's gonna take time for me to get used to aluminum, but this one I have to concede! (Btw, if you're interested in the word limey, click it!)