This is a technical question, so I assume it won't get many answers.

My old ash door (in my basement, near the bottom of the chimney, once used to empty ash from the fire that had been put down the ash dump) had rusted so much that when I prodded it with a crowbar it fell straight out and broke up into dust.

I want to replace it.

I have two choices: cast iron and cast aluminum.

What's the difference?