High hardness and thermal stability of nanocrystalline Mg-Al alloys synthesized by the high-energy ball milling

In present study, nanocrystalline Mg-xAl (x = 0, 5, 10 and 20 wt%) alloys were produced via high-energy ball milling (HEBM) followed by compaction under uniaxial pressure of 3 GPa at room temperature. The produced alloys were subjected to heat treatment (HT) for 1 h at various temperatures ranging from room temperature to 425 degrees C. The microstructure of the milled and subsequently heat treated alloys was studied using scanning electron microscope (SEM) and X-ray diffraction analysis (XRD). Lattice parameters changed upon addition of Al and in HT temperature, which have been discussed qualitatively based on electron to atom ratio curve. Hardness measurements, performed at room temperature using Vicker's microindenter, revealed that hardness of the ball milled Mg-xAl alloys was higher than many commercial Mg alloys. Hardness of the alloys was influenced by the Al addition and HT, and it was correlated with the crystallite size and microstructure. High hardness of Mg-xAl alloys was attributed to the grain refinement and Al addition.