I am interested in re finishing our aluminum swim platform. Plan on blasting it first for prep. There is some corrosion and pitting. Any advise as to what I can use for filling? Also how should we finish it. Will powder coat work on a filler? Or am I stuck with paint? Thanks.

It depends on how deep the pitting is. Powdercoat will fill in and level out small imperfections.

Too pitted to cover with powder coat...

Then use body filler to smoothe out the imperfections...and paint it.

you also have to be careful when powdercoating pitted or corroded aluminum. the heat/baking part of the process can cause out gassing in oxidized areas.

Blast, then Alodine conversion process, acid then converter, then filler, then awlgripTwo part epoxy primer, then sand, then primer again if you sanded through, then awlgrip