Evaluation of Multifunctional UV (MUV) Curable Corrosion

1. Evaluation of Multifunctional UV (MUV) Curable Corrosion Coatings on High Strength Aluminum Alloy Substrates K4P2O7 Na2H2P2O7 Na5P3O10 Organic Top Coat UV-Curable Coating Strontium Chromate Primer Non-Chromate Conversion Coating Chromate Conversion Coating Metallic Substrate Metallic Substrate M. O’Keefe (PI), W. Fahrenholtz, D. Heller, W. Gammil, A. Thomas J. DeAntoni B. Curatolo SERDP Project WP-1519 Objective CeCC XRD Analysis CeCC EIS Spectra CeCC Potentiodynamic Scans Conclusions Corrosion Performance Spray MUV Evaluation Filiform Corrosion 3000 hr Salt Spray 3000 hr Stripped Wet Tape Adhesion Develop a Two Layer, Chromate-Free, Zero TRI/VOC/HAPs Corrosion Coating System for DoD Metallic Substrates Epit Cr (VI) Control Epit = -275 mV Icorr = 0.74 µA/cm2 Epit ≈ -280 mV Icorr ≈ 0.45 µA/cm2 Epit = -343 mV Icorr = 2.14 µA/cm2 Epit = -322 mV Icorr = 1.17 µA/cm2 Epit = -261 mV Icorr = 0.60 µA/cm2 Epit = -420 mV Icorr = 1.36 µA/cm2 Current 3 Layer System Proposed 2 Layer System icorr • Post-treatment solutions affect pitting potential (Epit) and corrosion current (icorr). Overview • Phosphate post-treatment of spontaneous spray deposited cerium-based conversion coatings (CeCCs) on Al 2024-T3 increases their corrosion performance • The effect of phosphate source on the surface morphology, electrochemical response, and corrosion performance of CeCCs was characterized • Multifunctional UV coatings were spray deposited onto CeCCs on Al 2024-T3 • The performance of MUV coatings were evaluated for salt spray corrosion testing, wet tape adhesion, and filiform corrosion CrCC w/ MUV CeCC w/ MUV NH4H2PO4 As Deposited CeCC Surface Morphology • The MUV coating on a chromate-based conversion coating (CrCC) performs as well as the Cr (VI) Control in salt spray and adhesion tests • MUV coatings on CeCCs performed worse than the Cr (VI) Control and CrCC w/ MUV for each of the tests (CeCC too thick). • MUV coatings on thinner CeCCs (fewer spray cycles) have higher adhesion and do not blister after curing. • Orthophosphates charge transfer resistance >2X higher than pyrophosphates and >10X higher than polyphosphate or unsealed CeCCs • The formation of CePO4•H2O is believed to improve corrosion resistance Na3PO4 As Deposited Na5P3O10 Na2H2P2O7 • Electrochemical data correlate to results from salt spray corrosion testing and can be used to predict performance • The spray MUV coatings used with CrCCs offers comparable, or better, corrosion protection to the Cr (VI) Control without VOCs, HAPS or TRI chemicals in the coating. • Adhesion/blistering exhibited by the MUV coatings on CeCCs is related to the thickness; thinner CeCCs perform better K4P2O7 Na3PO4 NH4H2PO4 • Post-treatment reduces cracking of the CeCC compared to as-deposited films • Orthophosphate post-treatments showed the fewest pits and least salting after 14 days of salt spray exposure The guidance and support of Bruce Sartwell of SERDP and Donna Ballard of AFRL/ML are gratefully acknowledged