環保型鎂合金稀土金屬化成皮膜處理

Microstructure, properties and
formation mechanism of cerium
conversion coatings on AZ31
magnesium plates were investigated
with emphasis on solution pH,
temperature and the addition of
hydrogen peroxide. Experimental
results indicate that upon immersing in
the solution, AZ31 plates dissolved to
form magnesium ions and trace of
aluminum ions. Meanwhile, the pH at
the interface rose because of hydrogen
liberation. This increase in interfacial
pH caused the precipitation of
magnesium and aluminum hydroxides.
The coating formed in 0.05M cerium
nitrate solution consisted of three layers
with a porous layer overlaying the
magnesium substrate, an intermediate
compact layer followed by a fibrous
layer as the major overlay. The coating
formed in the solution with the addition
of hydrogen peroxide comprised
primarily the cerium oxide as the major
overlay and a porous magnesium
hydroxide layer intimately contacted
with the substrate.