【摘要】 采用电子扫描技术对加入稀土元素变质亚共晶 Al-Si 合金的非金属 Si 相的空间结晶形态进行了观察。SEM 观察表明,在每个共晶胞中 Si 相是内部相互联结的、成不规则排列均玫瑰花束状或分叉的纤维杆状生长。这就可以说明,稀土元素的加入并不影响共晶 Si 的成核而只是改变它的生长形态。根据这个事实和电子探针测得的稀土元素的分布结果,并结合非金属 Si 相的结晶行为,本文提出了稀土元素变质 Al-Si 合金机理的看法。稀土元素加入后被吸附在 Si 的快生长面(111)上,从而阻碍 Si 晶的粗大片状生长而朝向〈100〉的杆状方向生长。稀土元素是 Al-Si 合金的一个有效变质剂。增长冷速会使液/固界面变得更不稳定,导致 Si 晶的更加细小和分叉。故联合使用稀土元素变质剂和加大冷速将更能获得满意的变质效果。更多还原

【Abstract】 It has been reported that Rare Earth Elements(e.g.,Cerium,Lanthanum,etc.)are capable of modifying the euteetic structure of castaluminum-siliconalloys in recent literature[9,10,11] .Unfortunately,very limited detailsconcerning this modification phenomenon have been presented.Besides,onlyrough analyses of experimental results have been made.In order to searchfor the modification mechanism this paper presents observations made withelectron scanning techniques on the three-dimensional morphology of thenon-metallic eutectic Si phase in hypo-eutectic Al-Si alloys with Rare-Earth-Element modification.Scanning electron microscope observations show that the silicon phase isinterconnected[1,15] and this paper reveals that it is present as an irregularrosette or branched fibres in each eutectic cell.It can be proved that theaddition of Rare Earths does not affect the nucleation of the eutectic siliconbut changes its growth morphology[16] .Based on this fact and the resultsof Rare Earth distribution as measured by the electron probe and on the crysta-llized behavior of the non-metallic Si phase,the author proposes the followingviewpoint on modification mechanism of Al-Si alloy wirh Rare Earth Elements:Rare Earth Elements are adsorbed over the fast growing crystal(111)surfaces of Si,thus restricting the coarse plate growth of silicon but allowingit to grow in the(100) rod direction.Rare Earth elements act as effectivemodifiers of Al-Si alloy.The liquid/solid interface can become unstable whenthe cooling rate is increased and it brings abouta finer and more branchedsilicon crystal.Consequently,the author suggests that joint application of the Rare Earthmodifier and rapid cooling will bring about the optimum modification effect.更多还原