Microstructure evolutions of the Al-Mg and Al-Mg-Sc-Zr alloys during gradient cooling

In this work, the microstructure evolution of the Al-Mg and Al-Mg-Sc-Zr alloys during gradient cooling is studied and compared, the effect of the additions of Sc and Zr is also evaluated. The results show that the solidified microstructure of the Al-Mg-Sc-Zr alloy underwent more significant evolution than that of the Al-Mg alloy at gradient cooling rates (6∼438 K/s), and formed two fine grain areas at the cooling rates of around 230 and 6 K/s, respectively. A typical columnar-to-equiaxed grain transition behaviour was discovered at the cooling rate of 300 K/s in Al-Mg-Sc-Zr alloy. The solidified microstructure of the alloys was affected by the coordination effect of the cooling rate and the second phases.