In order to improve the grain refinement effect of Mg-Al alloys in aerospace industry

the calculation and analysis of Gibbs free energies of the metallurgical chemical reactions were carried out.The analysis results indicate that the de-composition reaction of MgCO

3

in Mg-Al alloys melt is hard to be controlled

which influences the refinement effect on Mg-Al alloys.Then gaseous CO

2

is thought to be the equal or even much better efficiency on the grain refinement of AM60 Balloy than MgCO

3

.MgCO

3

was added into AM60 Balloy melt

as well gaseous CO

2

with the same carbon content.The experiment results indicate that the average grain size of AM60 Balloy is decreased from 213μm to 113μm

while the microhardness is increased by 11.48% with the addition of MgCO

3

and the average grain size of AM60 Balloy is decreased to 91μm while the microhardness is increased by 8.32% with addition of CO

2

at equal carbon content.Based on SEM

EDS and XRD analysis

the refinement mechanism of MgCO

3

is the same as that of gaseous CO

2

that is

Al4 C3 generated by reaction of Al and C served as the heterogeneous nucleation substrates

which takes about the grain refinement of AM60 Balloy.