A brace of metal questions

I gather that pot metal is some kind of cheap alloy. Or is it just a term for cheap alloys in general? Are any specific metals always involved?

Has anyone else noticed that an alternative definition of tin is “a metal the speaker does not entirely trust”? I mean, the British used to refer to their Brodie helmets (made of mild steel, I believe) as “tin hats”, while Yanks commonly refer to steel cans as “tin cans”. Does anyone know why? Is this a chiefly British usage? Is it acceptable to use tin to mean “metal(s) of unknown type”?

Is plain old iron used for anything these days? Just wrought iron fences? What do they use pig iron for?

Here’s a neat thread I just found.

So if there are aluminum alloys, and zinc alloys, and aluminum is commonly alloyed with zinc, which is which? I mean, is iron commonly making it into aluminum and zinc alloys, or are we talking about mainly non-ferrous components? Is “x” always the most common component in “x alloy”?

Okay, I’m all out of metal questions for a few seconds.

Yes, I know tin is an element on its own. I was just wondering about colloquial usage.

Steel cans were commonly coated in tin to protect from rust. This practice has stopped as tin became more expensive.

I think the definition of tin as “a metal the speaker does not entirely trust” comes from the elements unfortunate tendency to change crystal structure at ~20 below zero (F). This causes objects made of tin to “bloom” and slowly fall apart when it gets extremely cold.
Does anyone else recall the sad story of the tin buttons used by napolean’s troops crumbling when they invaded Russia in the winter ?