Effect of ball-to-powder weight ratio on microstructure evolution of nanocrystalline Mg-Zn powders prepared by mechanical milling

126-134Nanocrystalline Mg-Zn powders have been prepared by mechanical milling using a planetary ball-mill with three ball-to-powder weight ratios of 30:1, 40:1 and 50:1 under argon atmosphere. The influence of ball-to-powder weight ratio on morphological changes, microstructural evolution and thermal behaviour of the milled powders has been examined by a combination of X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. The crystallite size and microstrain of the Mg matrix of the milled powders have been estimated using the Williamson–Hall method. The results show that in the first two hours of milling the crystallite size decreases rapidly and then slowly decrease with increasing milling time. After 18 h of milling, the crystallite size has been refined to 60-80 nm and remained unchanged. An excessively high BPR is not conducive to the deformation of the milled powders and the reduction of nanograin size. Additionally, the effectiveness of the milling process with different BPRs has also been discussed