Interdiffusion kinetics of the intermetallic coatings on AZ91D magnesium alloy formed in molten salts at lower temperatures

摘要

A continuous Mg-Al diffusion coating can be formed on the AZ91D Mg alloy by the diffusion coating treatment in molten salts in the lower temperature range from 280 to 400℃. The microstructure and composition of the diffusion coatings were investigated by scanning electron microscopy and energy dispersive X-ray analysis. The results showed that the diffusion coating consists of continuous γ-Mg_(17)Al_(12) phase and β-Mg_2Al_3 phase. The β-Mg_2Al_3 phase layer grows faster than the γ-Mg_(17)Al_(12) phase layer. The interdiffusion coefficients for each phase were investigated by Heumann's method. As the temperature increases from 320 to 400℃, the interdiffusion coefficient in γ-Mg_(17)Al_(12) phase (D_γ) increases from 2.2×10~(-12) to 9.6×10~(-11) cm~2/s. When the temperature increases from 360 to 400℃, the interdiffusion coefficient in β-Mg_2Al_3 phase (D_β) increases from 3.5 ×10~(-10)to7.4×10~(-10)cm~2/s. The activation energies for the interdiffusion in γ-Mg_(17)Al_(12) and β-Mg_2Al_3 phases are 155.9 and 66.3 kj/mol, respectively.