Before primer can be sprayed I believe it’s a good idea to give all the surfaces a jolly good clean. They’ve already been scuffed in previous session so the purpose of washing the parts is to remove all the aluminium dust and finger grease from the parts. By being clean that helps the primer bond with the surface and, hopefully, prevent any areas of poor adhesion.
First I clean the metal with standard paint thinners and a rag to remove as much of the aluminium dust as possible. Next I use Polyfiber 310 aircraft cleaner from Aircraft Coverings with a green scotchbrite pad to properly wash everything. I like the Polyfiber 310 because it is an Alkaline cleaner that really makes the aluminium visibly clean.
These parts have been cleaned and are hanging out to dry before priming tomorrow.
The picture really doesn’t do it justice, but these things really feel clean.