Yes Ji, your welding skills seem to be coming along nicely.
6061 is a structural grade alloy, as their is no strength needed for a muffler end cap then you can just as easily use maching grade Aluminium Alloy.
If you hunt around some of the Aluminium suppliers you can sometimes find short offcuts of materials that will come in handy for little jobs
While it's a nice job I actually think it looks a bit out of place on that muffler, it actually looks too good for the muffler. I think it would benefit if the whole thing was painted black.
I often get asked about doing budget repairs on mufflers, while they can be rebuilt it's the time factor of fiddling with them that is the killer. Materials are minimal but several hours and the costs build up as you can see. I have repaired a few mufflers like yours but I have taken them apart at the seams to take the dents out & fit new cores & packing. I usually do this because guys want the original look and the end cost is much the same as making one from scratch.
The packing in old mufflers often becomes fossilesed and useless and the perf cores are often broken or in poor shape.
The down side of this repair is that if the core is damaged then you would probably need to cut the other end off as well as the cores are usually welded in at both ends making replacing them difficult. With a good torch though you can usually see the core damage before you start to chop.
In short, it's a good budget fix for the home handy man that has time up his sleeve.
