Abstract
A new process called zinc diffusion cladding was developed which shows an effect similar to that of the conventional sacrificial claddings and it is easily applied to various aluminum shapes.
The process consists of the following two stages:
(1) A thin zinc film is deposited on aluminum surfaces from alkaline zincate solutions by chemical substitution.
(2) Zinc is diffused into the basic alloy.
Distribution of zinc solute in the cladding, which affects the pitting corrosion, depended upon the amount of zinc in the deposit as well as time and temperature for diffusion. The amount of zinc was increased with the rise of solution temperature and the increase of dipping time. When the temperature for diffusion was lower, the thickness of effective layer was decreased, which reduced the life of clad. Whereas, when the temperature for diffusion was higher than the melting point of zinc, the sacrificial protection was also decreased owing to a smoother gradient of zinc concentration in the diffusion clad.
Therefore, it was concluded that the depth of pitting corrosion was restricted by the diffusion cladding at 350400°C for 224 hrs. in a similar way to that of the conventional sacrificial claddings.
