Abstract
A high shearing dispersion technique (HSDT) was utilized for the first time to incorporate AlN/Al nanoparticles in Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (Elektron21) alloy. Compressive creep tests of unreinforced and reinforced Elektron21 alloys were performed at 240 °C with an applied stress of between 70-140 MPa. The results show that HSDT is an effective way to incorporate the nanoparticles and therefore to improve the creep resistance of El21 alloy by about one order of magnitude with 0.5% AlN/Al nanoparticles (NPs) compared with unreinforced alloy. The calculation of true creep stress exponent indicates that the viscous glide of dislocation and dislocation climbing are the rate controlling mechanisms during creep deformation. The microstructural observations show that the grains changed from equiaxed to dendritic grains with the addition of NPs by HSDT. Grain refiner Zr in Elektron21 alloy was partly consumed by Al atoms from the nano-powder mixture to form stable compound leading to grain coarsening. After high shearing, AlN NPs are effectively dispersed without any discernible clusters. The eutectic phases of El21 + 0.5AlN/Al composite become less continuous, much thinner, and are more homogeneously distributed in the alloy, which helps to pin the grain boundary sliding and hinder the dislocation movement inside the grain. The existence of AlN NPs is helpful for modifying the morphologies of α-Mg dendrites during solidification and thus resulting in obtaining thinner and hyper-branched eutectic phases in the nanocomposite. As a result, the creep resistance of reinforced alloy is additionally improved.
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