Polishing a Modern Alloy Segment?

I am in the rebuilding stages of a shell-off with my '73 Globetrotter. The rear street side lower segment was replaced at some point in the past. It has a very dull patina compared to the rest of the trailer, and I assumed this was because it had no clear coat on it and was able to oxidize. I also had a big messy dent in my curb side front lower segment, and after trying unsuccessfully to work the dent out, I replaced the segment with a brand new one. The trailer is made of 6061 T6, and I put a new panel in the center rear made of 6061 T6, which had a kind of brushed finish to it. I did a test polish spot on it, and it shined up really quick and easy, and matches the rest of the shell. The dull rear segment has been a pain, but it looks like it might shine up as well--just a lot of tough oxidization to get through.



That brand new segment in front looks like it is going to ruin my good time, though. I assume it is made of whatever modern alloy they make them of these days (5054? 3003/3004?), and accepted that it would not be a perfect match to the rest of the trailer. I did not figure that it wouldn't shine up at all. I tried a test polish spot on it, and after a good bit of polishing, it hardly looks touched. Has anyone out there tried and succeeded in polishing up a modern alloy segment?