Mg1.8Al0.2Ni alloys were synthesized by mechanical alloying (MA) with different ball-milling duration. The structure and thermal behavior were determined by X-ray diffraction and differential scanning calorimetry. The lattice parameters as well as the lattice volumes, the weight contents and the crystallite sizes of the existing phases were determined by XRD patterns refinement based on the Rietveld method. The results show that Mg2Ni phase was obtained after 8 h of milling. The variation of the ball-milling duration from 8 to 48 h leads to the formation of nanomaterials with an average grain size of 9 nm. Thermal stability study revealed three exothermic peaks for the alloys obtained after 6 and 7 h of milling and four exothermic peaks for higher duration of milling. The first, second and third crystallization reactions for Mg1.8Al0.2Ni obtained after 6 and 7 h of milling take place at 100-200°C, 200-300°C and 400-500°C for heating rate of 20°C.min-1. So, by optimizing the milling and annealing conditions, we were able to obtain the Mg1.8Al0.2Ni nanocrystalline phase after 8 h of mechanical alloying at 250 rpm, 6 h of mechanical alloying at 250 rpm and annealing at 500°C or 7 h of mechanical alloying at 250 rpm and annealing at 225°C.
S. Ben Aissa, M. Abdellaoui