Abstract
The scab corrosion resistance and the weight and depth of rust after the 600 hour salt spray test were determined for each combination of different surface treatments (only degreasing, BT # 3050-zinc phosphate of shower and half dipping type, BT# 3050+chromate rinsing, BT # 3450-iron phosphate, TD # 297-zinc phosphate of full dipping type) and different primers (Primer A-an anionic electrocoating, Primer C-a cationic electro-coating, Primer S-solvent based epoxy ester primer containing zinc chromate).
The test results thus obtained raise following informations.
1) In every combination of surface treatments, Primer A shows the worst scab corrosion and the largest rust formation in comparison with Primers C and S.
2) Primer C shows a very good corrosion resistance and is almost equivalent to Primer S in the scab corrosion resistance and the rust formation. This obviously indicates that converting an anionic EC to a cationic EC will produce a good result in anti-corrosion of automobiles, for example.
3) The weight of rust of Primer A is twice or more than those of Primers C and S. The depth of rust of Primer A, however, is one half of those of Primers C and S. This indicates that the rust grows rather horizontally with Primer A, giving it the worst scab corrosion.
4) It is proved that the effect of surface treatments on the scab corrosion is also remarkable. In particular, chromate rinsing is very effective to improve the corrosion resistance of Primers A and C.
