Weak strengthening effect of the precipitated lamellar phase in the homogenized Mg-8Gd-4Y-1.6Zn-0.5Zr (wt%) alloy followed by furnace cooling

The presence of small-scale precipitation is known to contribute to the high hardness and yield strength due to their hardening effect, which is widely applied in various engineering materials. The long period stacking ordered (LPSO) structure phases as well as stacking faults (SFs) are expected to play an important role in tuning the mechanical properties of Mg alloy. However, we found that the hardness and strength could not benefit from the lamellar LPSO structures and SFs precipitated in the matrix. Using transmission electron microscopy(TEM), high resolution transmission electron microscopy (HRTEM) and so on, we directly illustrate that the weak hardening effect is corresponding to the limited resistance of these basal precipitates in blocking the basal dislocation slip and the weaker solution strengthening of the matrix as the result of that much solute atoms have get into the precipitations. This finding demonstrates that the shape of the precipitations and their orientation relation to the glide planes of dislocation as well as the distribution of solute atoms are considerable factors to the strengthening effect.