Alluminium oxidises almost immediately on contact with air, certainly extremely quickly it will build it's own invisible to us film.
Which the main reason you will see anyone who works with it particularly welders constantly wiping and abrading it.
Ca is brilliant on cast metals I have seen big end bearings super glued back together and the engine run and lasted, I wouldn't recommend it or practice it myself but it was done on a race engine in the instance I witnessed.
When I mentioned tear out I was referring to a Celtic knot or similar segment not one that is drilled through so your sample would not be pertinent to that comment.
