Home Improvement Questions? Ask a Handyman for Answers
Hi. Without giving too much detail about the item, can you tell me a bit why it need to be closed. Will this piece be under stress in the final use or subject to heat. Does the plug need to be flush with the surface? What is this made of, steel, aluminum?
Using another filler like epoxy would work. Other than that you could also mechanically snap steel piece without soldering (especially if you make them slightly convex and you machine the inside slightly concave) by pounding it in with a hammer or a press (a very cold piece can make it tight even more when it expend to room temperature).
Soldering it like you mentioned can also work but require a good finishing step and you need to control the temperature to minimise warping.
Sorry about the wording, i often say soldering because i do so much electronic fix.
For the tickness, SMAW (stick welding) would do the trick. Like i said it can be a long process to finish a plate. Buffering and all (as flux may splatter around the hole perimeter), especially if you want two sides to look nice. That is why i suggested pressure insert like used for bimetal coin money.