looks like stainless steel with a (hopefully) small amount of surface pitting. You can get quite a bit more agressive with stainless than with aluminum. start gently with 600 grit wet sanding then 1000 and
1500. by then it should be looking pretty good. If you can bench mount a polisher go ahead and buff it up till it looks like you want
.
Alternatively, if you dont want a glossy shine a media blaster with soda or glass beads will give a very even gloss free finish. trying to match a machine finish as found on modern kitchen appliances can be very difficult.
Stay away from abrasive cleaning pads and products afterward. Barkeepers friend is an oldie and still a goodie
.
tim