| CPC C09D 7/61 (2018.01) [B23P 15/26 (2013.01); C09D 5/084 (2013.01); C23C 22/34 (2013.01); C23C 22/361 (2013.01); F28F 19/02 (2013.01); F28F 21/084 (2013.01); H05K 7/20254 (2013.01); C23C 2222/10 (2013.01); F28F 19/06 (2013.01)] | 8 Claims |

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1. A heat transfer system comprising a heat transfer fluid circulation loop and a heat exchanger comprising an aluminum alloy disposed in the heat transfer fluid circulation loop, wherein the heat exchanger is a round tube plate fin heat exchanger; and wherein said heat exchanger has a top surface of a mixed-metal oxide permanently integrated with the aluminum alloy on at least a portion of the heat exchanger, said mixed metal oxide top surface derived from a composition comprising a trivalent chromium salt and an alkali metal hexafluorozirconate in an aqueous solution; where the trivalent chromium salt comprises (NH)4Cr(SO4)2, KCr(SO4)2 and mixtures comprising any of the foregoing; wherein the heat exchanger comprises a first aluminum alloy component connected by brazing to a second aluminum alloy component and wherein the mixed metal oxide top surface is disposed over the first aluminum alloy component, the second aluminum alloy component, return bend tube portions, and the brazing connecting the first and second aluminum alloy components; and wherein the brazing comprises zinc.
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