Here's a free article from Hobart Filler Metals on troubleshooting aluminum welds:

https://tinyurl.com/y9lcr8as

I haven't read it but Hobart has been my go-to source for expert filler metal issues for decades. They want you to fill out a form but it's one of those pro-forma things. Just be sure to use the right email address.

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Ed Huntress