Bonding with Aluminum

Hello:

We are TIG welding some Aluminum water troughs with banked turns constructed with wedges of material welded together inside and out, then ground smooth on the inside.

The inside radii are cleaning up well and acceptable. The outside radii are not smoothing out well due to the angle of the wedges coming together when the weld is ground down there is a pronounced 'undercut' on each side of the welds.

The undercuts are not from the weld itself, it is more of a void where there is no material...kind of hard to explain.

Anyhow, what I am looking for is some kind of bonding agent that would look good and smooth and fill in the voids on either side of the welds. Things like bondo or JB Weld come to mind or something along those lines. Some kind of paste that will set up with time.

Has anyone had experience doing what I am trying to do? What kind of material would work well? A matching color to the unfinished Aluminum would be super cool.

The troughs are 5052-H32 Aluminum carrying water at ambient temperatures.

Thanks for any help.