- 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

Evaluation of Multifunctional UV (MUV) Curable CorrosionCoatings on High Strength Aluminum Alloy Substrates

M. O’Keefe (PI), W. Fahrenholtz, D. Heller, W. Gammil, A. Thomas

Develop a Two Layer, Chromate-Free, Zero TRI/VOC/HAPs Corrosion Coating System for DoD Metallic Substrates

Objective

Metallic Substrate

Chromate Conversion Coating

Strontium Chromate Primer

Organic Top Coat

Metallic Substrate

Non-Chromate Conversion Coating

UV-Curable Coating

Current 3 Layer System Proposed 2 Layer System

J. DeAntoni B. Curatolo

SERDP Project WP-1519

The guidance and support of Bruce Sartwell of SERDP and Donna Ballard of AFRL/ML are gratefully acknowledged

Overview

CeCC Surface Morphology

CeCC Potentiodynamic Scans

NH4H2PO4K4P2O7

Na2H2P2O7Na5P3O10

As Deposited

NH4H2PO4K4P2O7

Na5P3O10 Na2H2P2O7

Na3PO4

- Post-treatment reduces cracking of the CeCC compared to as-deposited films

CeCC XRD Analysis

Corrosion PerformanceAs Deposited

Na3PO4

CeCC EIS Spectra CrCCw/ MUV

CeCCw/ MUV

Spray MUV Evaluation

Cr (VI)Control

- Orthophosphate post-treatments showed the fewest pits and least salting after 14 days of salt spray exposure

3000 hrSalt Spray

3000 hrStripped

Wet TapeAdhesion

FiliformCorrosion

- Post-treatment solutions affect pitting potential (Epit) and corrosion current (icorr).

Conclusions- 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

- 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

- 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.

Epit = -343 mVIcorr = 2.14 µA/cm2

Epit = -420 mVIcorr = 1.36 µA/cm2

Epit = -322 mVIcorr = 1.17 µA/cm2

Epit ≈ -280 mVIcorr ≈ 0.45 µA/cm2

Epit = -261 mVIcorr = 0.60 µA/cm2

Epit = -275 mVIcorr = 0.74 µA/cm2

Epit

icorr