Keeping enamel from dent ?

Start by sanding the aluminum box with #400 sandpaper to give the paint something to hold on to. Then clean it thoroughly. 90% alcohol, Naptha, Acetone all work well on aluminum. Use latex or Nirtile gloves to prevent oil from your hands from contaminating the metal box.

Then use a metal primer paint designed for aluminum. Some automotive primers are 'self etching', meaning they chemically bind into the metal, promoting adhesion.

Then apply your finish design.

After the finish is completely dry, apply light coats of a clear finish compatible with the paint used for the design.

You will need to experiment with finish compatibility. Sometimes incompatible paints will cause the previously applied paint to wrinkle up or peel off.

Try to keep the total paint thickness as thin as possible. Often times chipping is due to very thick layers of paint.

Make friends with someone who knows about automotive refinishing. Since you are working with a metal box, many of the techniques used in auto repainting will apply to your projects.

Good Luck!!

 

Nope. Applying a hard coating over a soft one can cause the topcoat to deform; and if the previous coat is soft it's likely too thick and has trapped solvents. The hard coating will make the situation worse under heat, causing delamination, blistering, and "honeycoming " of the color coat.

The problem really lies with the color coat of enamel.