(I've done a bit of TIG welding and mainly use 6061.)
6061 can have up to 0.15% "Other", as long as no single "Other" component is more than 0.05%. So no more than 0.05% scandium if you want to call it 6061.
For instance, the addition of Sc and Zr to 6061 alloy shows a slower ageing response at 190 °C, resulting in lower yield strength of 321 MPa (aged for 5 h) than base 6061 alloys (350 MPa) [64]. On prolonged ageing (36 h), a significant drop (~ 19%) in the yield strength of 6061 alloys was reported compared to only a ~ 6% drop in ScZr-modified 6061 alloys. [1]
I wonder if I am reading this right or if 6061 is actually not very alloyable with scandium.
https://link.springer.com/article/10.1007/s12666-022-02547-z
Seems like the main difficulty in these alloys is that the Sc changes the solubility of the copper?
For context for those not familiar, precipitation hardening (aging) is the principal way to increase strength in Al alloys since you can’t quench harden them https://en.m.wikipedia.org/wiki/Precipitation_hardening