采用光学显微镜、扫描电镜、EDS能谱和差热分析研究了Mg-3Al合金中AlMn中间相的形貌特征,以及Mn含量对碳质变质剂异质形核作用的影响机制.结果表明:加碳变质处理产生的碳化铝可成为α-Mg的有效形核核心;当合金中的Mn含量小于0.32％(质量分数)时,加碳变质处理能使α-Mg晶粒明显细化,最小平均晶粒尺寸达到66 μm,此时形成大量细小的球状和杆状AlMn中间相,有助于晶粒细化;但当Mn含量增加到0.56％时,形成更多粗大的十字花瓣状AlMn中间相.过量的溶质Mn易与A14C3粒子结合形成不利于形核的Al-Mn-C-O复杂化合物,并导致α-Mg晶粒粗化.
The morphological characteristics of AlMn intermetallics in Mg-3Al alloys and the influencing mechanism of manganese on heterogeneous nucleation of aluminum carbide (Al4C3) were studied by OM,SEM,EDS and DTA.Results show that Al4C3 particles are produced by carbon inoculation and then they act as the potent heterogeneous nuclei for primary Mg.The a-Mg grain can be greatly refined with carbon inoculation when the content of Mn is below 0.32 wt％.The minimum average grain size of 66 μm can be obtained due to the formation of numerous small ball-like and short rod-like AlMn intermetallics,which is helpful to grain refinement.In contrast,coarser cross petals-like AlMn intermetallics are formed when the content of Mn is increased to 0.56 wt％.Therefore,the Al4C3 particles are easily poisoned by excess Mn solute and turn to be complex Al-Mn-C-O compounds,which are not effective heterogeneous nuclei of primary Mg,hence leading to the coarsening of a-Mg grain.
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