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This work proposes an approach to minimize surface energy deactivation of plasma-treated metal and carbon fiber-reinforced polymer (CFRP) surfaces by vacuum sealing. Plasma treatments enhance adhesive wettability on post-treated surfaces for adhesive joints, but the treated surfaces deactivate quickly in air. The surface energy of aluminum alloy AA6061 and carbon fiber-reinforced polymer-polyamide (CFRP-PA66) optimally treated by a blown air plasma instrument returns to the original surface energy within 1 h. Vacuum sealing of AA6061 and CFRP-PA66 reduced the surface energy deactivation over 7 days by at least 230 times and 970 times compared to in air. Double Cantilever Beam (DCB) tests performed on adhesively-bonded AA6061/CFRP-PA66 joints showed that the total energy release and energy dissipation before failure of plasma-treated and vacuum-sealed materials was up to 60% more than plasma-treated materials without vacuum sealing and up to 125% more than non-plasma-treated materials. • Vacuum sealing significantly slowed down the deactivation of plasma-optimized surface energy of AA6061 and CFRP-PA66. • Vacuum sealing preserved hydrogen-bonded carbonyl groups on the plasma-treated CFRP-PA66 surface. • Vacuum sealing protected over-oxidation of carbon to carbonate on AA6061 surface after the plasma treatment. • In the interface between adherend surfaces and adhesive, hydroxyl groups reacted with dicyandiamide to form amide bonds. • Vacuum sealing maintained the plasma-enhanced Mode I fracture energy of adhesively-bonded AA6061-CFRP-PA66 dissimilar joints. [ABSTRACT FROM AUTHOR]