5200 is recommended to be installed on metals using a primer first. 3M's material specifications recommend:

Scotch-WeldTM Structural Adhesive Primer EC-
1945 B/A

http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSufSevTsZxtU48_eoYtvevUqevTSevTSevTSeSSSSSS--

This is why I stick with epoxy based adhesives when making repairs.

good info, thanks guys.

My son and his buddy put 2 holes through bottom of their aluminum boat with hatchet chopping out ice 4 years ago . They sealed it up with JB Weld. Both holes were about two inch long they dollied metal flat the ran zip cut disc up slit to permit weld to bond to both sides . Still holding fine

JB weld is epoxy - good stuff - it's only problem on aluminum is that it's rigid, while the aluminum isn't, but if they had a generous enough amount on there it's not going anywhere.