A few years back, I had to try and weld a bunch of walker/roller cart things at work. They showed up spread out over around 6-8 months.
https://www.amazon.com/Drive-Medical-Rollator-Removable-Support/dp/B005S1CHKC?th=1
I cant find the exact ones but the link is the evolved versions of what I tried to fix. It started as one that came back to the shop at least 3 times because the welds kept breaking. The first time went easy enough and it welded OK for what it was, my problems were more dealing with trying to get a ground/position the thing to weld on it... Then it came back. Repair, and Again its back
The way the part was, a few 3/8" bolts could kinda hold it together once it failed again and that's what kept it from coming back to my weld table, and telling them to get a new one...
Then a bunch more from different people showed up, same design same failure.
The factory welds had some sketchy spots, but they were put in with some degree of skill and fairly decent equipment. Most of the welding issues were due to the cad/design people not knowing how to weld aluminium and not so much on the welder, around 75/25 design/skill. I finally got one with an original manufacture sticker still on it and was able to look them up on the interwebs. Made from 7075 tubing likely with no knowledge of what happens when welding it. It didn't crack right away so it must be good, roll with it!
Saw maybe 5 total and only worked on about 3 because we learned (eventually) what to tell people as to why its just going to break again, and that they should go get new ones.
Now I might be able to weld something like them the next time!
That is pretty cool in all seriousness, and I like the idea that some day I might be able to buy filler wire for 7075...
