Accession Number : ADA267205


Title :   Assessment of Chromate and Non-Chromate Conversion Coatings for Al Alloys Using Electrochemical Impedance Spectroscopy


Descriptive Note : Final rept.,


Corporate Author : ARMY RESEARCH LAB WATERTOWN MA MATERIALS DIRECTORATE


Personal Author(s) : Chang, F ; Levy, M ; Huie, R


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a267205.pdf


Report Date : Jun 1993


Pagination or Media Count : 23


Abstract : A study was conducted to evaluate whether a non-chromate conversion coating (Sanchem) for Al alloys (Al 2024 and 7075) could be a suitable replacement for the currently used chromate conversion coating (Alodine) without compromising corrosion resistance. Electrochemical impedance spectroscopy (EIS) and salt spray testing were employed to compare the corrosion behavior of coatings consisting of (a) pretreatment only (Sanchem or Alodine), (b) pretreatment (Sanchem or Alodine) plus primer (epoxy polyamide or waterborne epoxy), and (c) pretreatment (Sanchem or Alodine) plus epoxy polyamide primer plus polyurethane topcoat. Results indicated that the experimental impedance values provided a reliable estimate of the film integrity and corrosion protective capability, that the Sanchem conversion coating generally compared favorably with the Alodine coating, and that higher impedance values attributed to the application of topcoat of both alloys which were treated with either Sanchem or Alodine and epoxy polyamide are characteristic of low conductivity, good barrier type coatings. However, additional tests are required before the Sanchem can be recommended as a reliable alternative to the Alodine coating.


Descriptors :   *CONVERSION , *ALUMINUM ALLOYS , *CHROMATES , *COATINGS , *CORROSION RESISTANCE , TEST AND EVALUATION , CONDUCTIVITY , BARRIERS , VALUE , WATERBORNE , SPRAYS , IMPEDANCE , SALTS , REPLACEMENT , ESTIMATES , PRIMERS , ELECTROCHEMISTRY , SPECTROSCOPY , RESISTANCE , FILMS


Subject Categories : Physical Chemistry
      Coatings, Colorants and Finishes
      Properties of Metals and Alloys
      Atomic and Molecular Physics and Spectroscopy


Distribution Statement : APPROVED FOR PUBLIC RELEASE