Better would have been to run 2x2s on top of the joists with no nails or screws thru the the tin and would allow water to get out. To late now as your deck would have to have been built 2" lower.
Read the box that coil stock can in. In big letters it will say do not put in direct contact with pressure treated lumber.
Joe: That's why they put poly over and under the sheet stock.
This should help answer any questionshttp://www.finehomebuilding.com/PDF/Free/021160082.pdf
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