I'm trying to learn the second part of the Sixpounder solo (the one with all the key changes) and I was wondering if Alexi sweeps the riffs, or string picks?

Both sound right, but I wanted to know what he does on the recording.

Are you asking if he sweeps or string picks the entirety of the 2nd solo? If so, he does not.
He sweeps right when the bar ends then the solo melody starts again.
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