Grounding Lugs - tin coated copper?

[Walt_Solartown]

Why are grounding lugs 'tin coated' copper? Is this to prevent corrosion buildup? We commonly run 6AWG bare copper wire on installations and it is attached to each panel using the common Unirac grounding lug. How effective are these lugs since they are screwed into the aluminum frame of a UL-listed solar panel? Isn't aluminum less conductive than copper? Sorry for the multiple questions - I know grounding can be hard to nail down! And is there a cheaper alternative to these lugs? They are expensive!

[Sunking]

The tin coating is for connection mating resistance and corrosion.

To use Cu wire and Cu terminations terminated to Al has to be listed for such purpose along with liberal use of a oxidation inhibitor compound like No-Lox.

Yes Cu is a better conductor than Al, however as long as Al is sized correctly and terminated correctly is no problem.

All the info you seek is in NEC.