Dear all,
I am working on aluminizing AZ31 with Al powder. I have tried:different diffusion coating temperatures from 250C to 500C, NH4Cl and AlCl3 as activator, vacuum and Ar as the environment and ethylene glycol to enhance contact between Al powder and AZ31 surface.
However, still no layer is observed under the microscope. Any hint on this problem?
I am not an expert, but maybe you are having problems with oxide surface coating in substrate and aluminum powder, alumina (Al203) and magnesium oxides coating is likely preventing or retarding diffusion.
Remove the oxide layer in the substrate.
You can try ultrasonic vibration and pressure for the powder
I do not know the composition of the matrix (AZ31), from which depends diffusion? Removal of the oxide layer it is mandatory before treatment.
Activator of the process is more suitable AlF3 (3-5%).And compositions for treatment to be prepared as a paste (in aqueous ethyl alcohol)
AZ31 is 94% Mg-3% Al-1% Zn. I use AlCl3 as activator and also use ethylene glycol to make a paste of mixed master alloy and activator. Before start the process, the surface of the AZ31 base alloy is ground to make a fresh metallic surface.
Generally magnesium aluminum coating can lead to galvanic corrosion of the magnesium alloy in the operation. For lasting the aluminum compound to magnesium must form a transition layer between them this can be accomplished only at elevated temperatures in a protective atmosphere. To remove the aluminum oxide from the surface of the powder particles can be used alkali treatment. The oxide layer on the surface of magnesium loose and prevent the coating is less than the oxide layer on aluminum.
Should be replaced with aluminum powder treatment. For example, a mixture Al2O3 + B2O3 (70 i 30%) and activator Na2F.
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