Precipitation behavior and effect of new precipitated β phase in AZ80 magnesium alloy

Granular precipitate that was a new kind of β-Mg17Al12 phase found in aged AZ80 wrought Mg alloy at all aging temperature was studied. The structure and precipitation behavior of this granular β-Mg17Al12 precipitate were studied by environmental scanning electron microscopy （ESEM） and transmission electron microscopy （TEM）. The effect of the granular precipitate on mechanical properties of AZ80 alloy was also studied. The new precipitate that was granular and nucleated both on grain boundaries （GBs） and twin boundaries, has the same crystal structure and lattice parameter as those of the continuous or discontinuous precipitated fl-Mgl7All2. And the nucleation and growth of the granular precipitate are faster than those of the other two precipitates at higher temperatures （above 583 K）, but are suppressed at lower temperatures （below 423 K）. At lower temperatures, the discontinuous β-Mg17Al12 precipitates firstly and the granular β-Mg17Al12 precipitates after aged more than 40 h. The crack is easily nucleated on the phase boundaries of granular phase and matrix because of the weak binding force. As a result, the strength and ductility ofAZ80 Mg alloy are decreased by the granular β-Mg1TAl12 precipitate.