Accelerated Corrosion and Adhesion Assessments of CARC Prepared Aluminum Alloy 2139-T8 Using Three Various Pretreatment Methods and Two Different Primer Coatings

Aluminum alloy 2139-T8 panels of 0.25” thickness were machined from 1.0” rolled plate and coated in accordance with Chemical Agent Resistant Coating (CARC) specifications for evaluation under three different pretreatment conditions. The pretreatment conditions were abrasive blasted, a chromate free pretreatment (CFP), and a commercial trivalent chromate pretreatment (TCP). In addition to the three distinct surface pretreatments, 2 different primers were also evaluated under the same pretreatment variations. The primers used were MIL-DTL-0053022C and MIL-PRF-23377J Class N. Both sets were then topcoated using the polymeric bead based MIL-DTL-53039 Type II. Corrosion resistance was evaluated under GM 9540P and ASTM B 117 neutral salt fog (NSF) methods. Adhesion was assessed under dry conditions using ASTM D 4541 pull-off and under wet conditions using ASTM D3359A. Prior to coating, the conversion coated surfaces were compared for uniformity and color versus identically prepared AA2024-T3 and AA2519-T87 samples to determine whether or not the alloy differences would warrant modifications to current pretreatment processes.