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The advent of cathodic electrodeposition in the automotive industry has brought about substantial changes in the pretreatment of steel and galvanized steel surfaces and the testing thereof. Cyclic scab blistering tests, water soak tests, coating solubility, coating porosity and ESCA/SEM/Auger surface analysis techniques have provided significant insights into the factors that optimize the performance of zinc phosphate coatings for cationic paint systems. Specifically, the crystal structure and iron content of the phosphate coating and a chromium based post-rinse have been shown to make a significant effect upon the subsequent corrosion resistance properties of the phosphate/metal/CED paint system. Further, ESCA/SEM surface analysis and accelerated testing have shown that the processing method substantially affects both the crystal structure and composition of the coating.

The inherent metal quality, coupled with the metal surface condition prior to phosphating has been associated with the corrosion stability and adhesion characteristics of the subsequent phosphated and painted surface. The corrosion and adhesion properties are usually determined via long-term tests; however, our investigation of the potentiodynamic behavior of the metal substrates and phosphated coatings have shown that these electrochemical measurements can provide possible failure-mode explanations exhibited by subsequent accelerated testing. Fundamental properties of phosphate coatings on Fe, Zn, and Al substrates have also been investigated via potentiodynamic measurements. Indications of the reactivity of the different substrates with respect to ease of phosphateability may be derived via anodic and cathodic polarization measurements. Further, the effects of variations in the phosphate processing conditions have been correlated to polarization measurements.