| At present up to, magnesium alloy is the lightest structure material, and Mg-Al alloy is the most important one because of the earlily developing and the widely application. Particularly, grain refinement is a significant and effective method to improve the slab quality and the various mechanical properties in the later use. Carbon inoculation method can be the most developing prospect in Mg-Al alloy owing to its simple operation, the cheaper cost, and the advantages of less fading with long time holding. But in the industrial production, there is no effective commercial grain refiners in the refining process so far, as the mechanism of grain refinement caused by carbon inoculation have not been investigated completely. In this article, the high-purity Mg-9A1alloy is chosen, and then on the basis of native grain refinement, the alloy melt was added with different lever of Mn/Fe element. And the mechanism of changing in the grain size affected by Mn/Fe is investigated.Then the Mg-9A1alloy melts with the different lever of Mn/Fe element were treated with the carbon inoculation, so the C2Cl6was added into the melt of Mg-9Al alloys. The mechanisms of Mn\Fe and carbon inoculation on the grain refiment of Mg-9A1alloys are investigated in this research. The main results in the paper are as follows:(1) When the high-purity Mg-9A1alloys is added with the different lever of Mn, Mn has no effect on the grain size of the alloys. High purity Mg-Al alloys have a naturally fine grain size compared with the commercial alloys with the same basic composition, and this is refereed to as native grain refinement. And the mechanism of native grain refinement is attributed to the Al-C particles existing in the alloys. When Mn enters into the alloy melt, Mn may be absorbed in Al-C crystal nucleus with physical adsorption or chemical reaction to form Al-C-Mn particles. Compared with the Al-C particles, the potency of Al-C-Mn compounds is decreased with the Mn content increased. But in the experiment, the growth-restricting of Al and the pining effect of Al-Mn particles precipitating from the melt in the process of the solidification can limit the grain growing. So from the experiment result, the pining effect of Al-Mn and the growth-restricting of Al can completely eliminate the negative effects from the Al-C-Mn particles.(2) When the melt is treated with the carbon addition, the new generations of Al-C particles have no effect on the grain size of the Mg-9Al alloy. Because the grain sizes of alloy contain the different lever of Mn have already reached the great grain refinement compared with the high-purity Mg-9A1alloy as the results of pining effect and growth-restricting of grain growth. So in the process of solidification, the further refinement of the grain is limited by the latent heat of phase changing.(3) When the melt is treated with the different lever of Fe, on the basis of native grain refinement, the grain size is changed regularly. When the Fe content is lower, Fe has no great influence on the Al-C nucleus. When the addition quantity of Fe is from0.1wt%～0.30wt.%(detectable quantity:0.0014wt.%～0.030wt.%), Fe could be adsorbed on the Al-C particles to form the new particles of Al-C-Fe. The crystalline structure of the Al-C-Fe particles differs from Al-C particles with the containing of Fe increased, eventually the changing of Al-C-Fe particles will have the great disregistries with a-Mg to cause the grain coarsening. When the addition quantity of Fe is more than0.3wt.%(detectable quantity:0.030wt.%～0.038wt.%), with the rise of Fe containing in the Al-C-Fe compounds can improve the changing of compounds to contain a higher Fe, so the nucleus structure change again to the direction of crystal nucleus. The Al-C-Fe intermetallic compounds act as the crystal nucleus to refine the microstructure.(4) When the addition quantity of Fe is lower, Fe has no great influence on the native grain refinement. As the melt is treated with carbon inoculation again, the new generations of Al-C particles have no effect on the grain refinement with the limitation of latent heat. In the end, the grain sizes of the alloy have no changing. When the addition quantity of Fe is increasing gradually, the existence of Fe in high purity Mg-9A1alloys can impact on the Al-C particles in the structure and properties to cause the grain coarsening. When the melt is with carbon addition, the new generation of Al-C particles would have a certain refinement on the grain size. With the addition quantity of Fe increasing, the heterogeneous nucleations which the potency in the crystallographic structure is reduced obviously have been changed in the high-purity melt to act as the nucleation again. When the melt is treated with carbon inoculation, C would be the impurity element in the Al-C-Fe particles to reduce the potency of the compounds and it is negative to the solidification and grain refinement. |
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