RETRACTED: Investigation on Heterogeneous Nucleation of MgAl2O4 in Al-Mg Alloys (Retracted article. See vol. 22, pg. 348, 2016)

This work investigates the mechanisms of grain refinement of Al-Mg alloys through ultrasonic treatment and varying Mg content. MgAl2O4 particles display an equiaxed and faceted morphology with {111} planes and when exposed to {111} of alpha-Al, can act as heterogeneous and potent nuclei for aluminium. Intensive vibrations by ultrasonic treatment lead to significant grain refinement through effective dispersion of MgAl2O4 particles. The equiaxed and faceted morphology of MgAl2O4 along with a well-defined cube-on-cube orientation relationship (1 (1) over bar1)[110] MgAl2O4//(1 (1) over bar1)[110] alpha-Al, provide improved refinement. Furthermore, multiplication of solidification sites by the ultrasonic pulses enhances heterogeneous nucleation. The resulting improved grain refinement relates in all probability to the increased nucleation sites, due to grain multiplications and wetting of impurities, the lowering of surface tension due to the segregation of magnesium to the surface of liquid aluminium, the appropriate growth restriction factor and the low lattice mismatch coupled with strong dispersion of oxides.The filtration test confirms these particles as potent refiners.