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Automotive phosphating technology 1975-1995
Published October 14, 1993 by SAE Australasia in Australia
Both paint appearance and corrosion performance of automobiles depend on the application of a high quality surface conversion coating. The impact of the choice of metals for automobile body construction on these product properties and environmental concerns have driven developments in surface treatment technology. The performance of steel as an exterior automotive surface was maximized by conversion coatings with a high iron content. When the predominant use of cold rolled steel was replaced by the introduction of electrogalvanized and other coated products, changes in cleaners and further changes in phosphate bath and coating composition improved the performance of these new surfaces. The tri-cation (Zn, Ni, Mn) phosphating systems were introduced to provide the highest quality coating in a mixed metal system. In recent years, changes in materials of construction have slowed because corrosion goals have been met and, as a consequence, industry needs for new technology have shifted. Operational and environmental considerations now play a larger role among the current driving forces in the development of new conversion coating products.
This paper traces the sequence of improvements which have been introduced in automotive pretreatment and demonstrates these improvements with results from accelerated corrosion tests.