Grantee Research Project Results
Final Report: Chromium-Free Conversion Coating Technologies for Light Metals
EPA Contract Number: 68D02007Title: Chromium-Free Conversion Coating Technologies for Light Metals
Investigators: Coolbaugh, M. Todd
Small Business: American Research Corporation of Virginia
EPA Contact: Richards, April
Phase: I
Project Period: April 1, 2002 through September 1, 2002
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text | Recipients Lists
Research Category: SBIR - Pollution Prevention , Pollution Prevention/Sustainable Development , Small Business Innovation Research (SBIR)
Description:
This Phase I project investigated the feasibility of preparing nonchromium conversion coating materials for lightweight aluminum and magnesium alloys. The technical approach involved the manipulation of coating compositions and process conditions favoring interfacial precipitation reactions at the alloy surface to develop conversion coating formulations that are effective, simple to use, and environmentally sound. The project was innovative in that it combined complex metal fluorides with film-forming agents to provide a nonchromium conversion coating that is amenable for use in industries requiring one- or two-step process conditions, enhanced coating reliability and performance, and low environmental and safety-added costs. The new conversion coating materials would find applications in metal finishing job shops and in the production of automotive components.
Phase I objectives included the formulation of chromium-free coatings, evaluation of the coating corrosion prevention and adhesion performance, and the acquisition of families of test data to be used in the optimization of corrosion-prevention coatings for lightweight alloys. Phase I results proved the feasibility of the interfacial precipitation approach through the development of three new nonchromate conversion coatings and demonstration of the survival of these coatings through 336 hours of neutral salt spray corrosion tests on AA6061 and A360 alloys. Experiments performed during Phase I indicated the effectiveness of immersion coatings that utilize complex metal fluorides to provide enhanced corrosion protection of AA6061.
Summary/Accomplishments (Outputs/Outcomes):
The Phase I project was successful in extending prior work by the American Research Corporation of Virginia that developed formulations for spray-on conversion coatings for aerospace aluminum alloys. In the current project, a formulation for immersion coating aluminum alloys used in the automotive industry was developed and demonstrated. Two additional formulations based on the combination of complex metal fluorides and inorganic film-forming compounds also were developed and tested. It was found that conversion coatings based on two differing complex metal fluorides provided enhanced corrosion protection over either of the individual fluorides alone.
Conclusions:
The overall conclusion of the Phase I project was the finding that nonchromium conversion coatings based on interfacial precipitation could be used to protect lightweight metal alloys such as AA6061, AA6111, and A360 that are used in the automotive and marine motor industries. The primary result of the Phase I project was the finding that aqueous solutions containing combinations of complex metal fluorides can provide excellent corrosion protection for AA6061 and A360 when used in concert with a range of film-stabilizing agents. Work was performed to identify candidate materials that could be used to increase interfacial precipitation reactions through supersaturation of sparingly soluble reagents. It was found that film-stabilizing agents could enhance coatings that were based on the complex metal fluorides.
Supplemental Keywords:
automotive aluminum alloys, magnesium alloys, conversion coatings, fluoride, chromium, light metals, SBIR., Sustainable Industry/Business, RFA, Scientific Discipline, Toxics, Technology for Sustainable Environment, Chemical Engineering, Engineering, Chemistry, Sustainable Environment, HAPS, Environmental Chemistry, 33/50, cleaner production/pollution prevention, Environmental Engineering, chromium & chromium compounds, nanomaterials, Chromium, coatings, environmentally benign alternative, Chromium Compounds, hexavalent chromium, chromium plating, conversion coating, alternative chromate conversion, chromate, metal finishingThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.