Keeping castings shiny after machining

Dear Sir,

We use 100 MT of various types of aluminium pressure die castings every month.We do shot blasting of castings before machining, using stainless steel shots.Castings are bright before machining and get dull and tarnished after machining.We request you to give solution for castings to be bright and clean even after machining.

With Regards,

Machined aluminum surfaces of any alloy should be fairly bright as soon as it comes off the machine. If not, are you allowing the part to get quite hot while machining? If not, I would look at the cutting fluid. Either the wrong one or not enough of it on the part. Finally, what are you cleaning the cutting fluid off of the part with, or are you just letting it dry on?