Your forge wasn't hot enough and what was left was contaminated by oxides. Run a hotter forge, add extra zinc after the scrap has melted ( I use sacrificial annodes from boats as they are pure zinc), use a lid on your crucible and cast in a well ventilated area

1.  I'm glad to know that there are at least two of us who enjoy my humor. :)

2. Tin foil and tin cans are are made of aluminum because -
Way back when in the late 19th century when they first came into widespread manufacture and distribution, they were made of tin. Tin was comparatively cheap, while aluminum was vanishingly expensive.

Aluminum is very difficult to refine by the methods known at the time, and was rare and precious. Then in 1890-something, a couple of guys figured out a way to refine aluminum very cheaply by applying largish amounts of electricity to the reaction.

Over the next several decades, aluminum became widely and inexpensively available; while worldwide tin resources were rapidly becoming depleted, with the rise in price that supply-&-demand economics would lead you to expect.

By the last quarter of the 20th century,  machinery and manufacturing processes had been fully converted to "tinning" everything in aluminum or (in cases where aluminum isn't strong enough) in steel. If you find a tin can that's actually made of tin, it's an antique that's probably worth a couple of bucks at a dealer's. Tin foil made of tin is worth many antique-dealer bucks, but was very fragile stuff and unlikely to have survived.

It's also a little bit of one of those "separated by a common language" things: American cats (like the one currently trying to block my view of my monitor :) are often fed canned cat food; while cats who must share their soveriegnty over their subjects with HM Queen Elizabeth are more likely to demand and receive tinned cat food.

3. I meant the tables in the links Lemonie gave, which is not really what I turn out to have said at all (oh, to be able to edit one's posted commments).

For instance, if you have what looks like a cast aluminum water tank, it's proabably the alloy listed in the tables as used for casting of tanks. If you have a welded aluminum tank, it's proabaly the weldable alloy listed for tanks. It's a limited sort of bass-ackwards reverse engineering, but is probably the best you can do outside of chemical or x-ray analysis.

Someone asked a similar question earlier this year, I remembered that information was out there somewhere.

L