Just so you know, the best tool to cut aluminum is a woodworking drop saw, with a relatively fine pitch and still sharp blade. If the blade has never been warped, and you clamp the metal piece and use the saw's feed slides, moving the cut forward slowly, you can get a really clean cut face that looks like it was milled.
I guess you don't have access to one of those?
Of course, best done somewhere the millions of tiny metal shavings aren't a disaster, can be cleaned up easily.
Lacking a dropsaw, use the coarsest new hacksaw blade that still puts at least 2 teeth across the cut. Squirting some kerosene into the cut, and also when you are filing, makes it go much better.