Effect of heat treatment on microstructure of AZ91D alloy

Effect of heat treatment on microstructure and phase structure of AZ91D magnesium alloy was investigated by means of optical microscopy,X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The results show that β-Mg17 Al12 phase in AZ91D magnesium alloy is almost dissolved and substitution solid solution forms after solution treatment at 420 ℃ for 20 h.When aging at 175 ℃,with increasing of aging time,the precipitation mode and morphology of the precipitates changes.TEM observation shows that a short rod-shaped precipitate of β-Mg17 Al12 occurs in the AZ91D alloy aged for 18 h,and the precipitate keeps[011]β//[13 42]α relationship with α-Mg matrix.