Corrosion Resistance and Adhesion Properties of the Chromium-Free Coating Using an Urethane-Base Resin for AZ91E Magnesium Alloy

摘要

Corrosion resistance and adhesion properties of a chromium-free (poison-free) coating using an urethane-base resin for AZ91E Magnesium alloy have been investigated by salt immersion tests and thermal and humid resistance tests. As a result of the salt immersion tests, the corrosion resistance of the chromium-free coated specimen was almost equal to that of the Chromium-based chemical conversion. Also, the thermal and humid resistance tests showed that no changes were found in the coating with an urethane resin base layer; however, exfoliation was observed in the coating with a phenolic resin base layer. In the coating with an urethane resin base layer, the boundaries between the base layer and the aluminum middle layer were relatively flat and there were no pores, though a lot of pores were observed between the base layer and the aluminum middle layer in the coating with a phenolic resin base layer. Therefore, it is suggested that the good adhesion properties of the chromium-free coating are related to the strong adhesion between the urethane resin base layer and the aluminum middle layer.