The surface of a sand core prepared by triethylamine cold box core-making technique was coated with a kind of special coating containing an oxidizing agent Na

2

Cr

2

O

7

and then the coated core was assembled in the mold and a reaction could be observed when the alloy melt entried the mold

Then an oxide layer of about 2μm on the surface of the aluminum alloy was generated

which improved greatly the corrosion resistance of the sample.The morphology and corrosion resistance of the oxide layer were investigated using SEM and electrochemical impedance spectroscopy.The results reveal that with the same rate of pouring

as the thickness of the sample increase

the thickness of the oxide layer is increased.With the increase of the height of the sample

the thickness of the oxide layer is reduced along the heiGHTdirection.During using internal oxidation treatment

a faster casting speed should be adopted to ensure that the aluminum liquid reacts with the coating as soon as early.