Improved Mg-Al-Zn Magnesium Alloys Produced by High Energy Milling and Hot Sintering

Powders of commercially pure magnesium (c.p. Mg), AZ91 magnesium alloy and zinc were milled using a high-energy mill. The effect of high energy milling (HEM) on powders morphology, chemical composition, crystallite size and compaction of different powders mixtures were studied. After compaction, samples were thermally treated at 450 degrees C and both density and hardness were evaluated. It was found that as milling speed and time increases, the AZ91 alloy and c.p. Mg particles were deformed and fractured up to sizes below 10 mu m. X-ray diffraction patterns for both the c.p. Mg and the AZ91 powders revealed that the milling process induced changes in both the alpha-Mg and the beta-Mg17Al12 phases. By increasing the milling speed, the crystallite size decreases by up to 70% for AZ91 powders and by 80% for magnesium powders. The relative densities of the compacted AZ samples were greater than 85% and this parameter increased for all samples after thermal treatment at 450 degrees C, obtaining densities higher than 88%. Hardness measurements disclosed values as high as 84.3 HR15T. Theoretical calculations of mechanical strength were obtained for all samples based on the hardness values measured, finding very encouraging results for the three Mg alloys.