材料期刊网

用稀士熔盐电解法及熔盐直接反应法对Al-Si液态共晶合金分别定量添加了La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Ho,Er和Y共十一个单一稀土以及一个混合稀土的变质剂。通过显微结构分析系统地研究了在70—80℃/min冷却速度下合金的变质效果。发现Eu,(Yb)具有最强的变质能力,La次之,并发现其均为“长效”变质剂.Ce,Pr,Nb及混合稀土的变质能力稍低于La。稀土元素的变质能力随原子半径的减小而迅速降低.Sm以下已减弱至微不足道的程度。Eu和(Yb)的变质能力主要是与其原子半径的突跃增大有关。Er,Y不具变质能力。根据Eu和Ac原子半径的接近以及Y-La-Ac的同族规律,推测Ac将具有还要大的变质效果。据此总结了强变质剂Na,Sr,Ac在元素周期表中的斜线位置,认为变质剂元素的变质能力主要取决于其价电荷数,原子半径和原子序数的一定组合。

A systematic study has been made of the modification of Al-Si alloys with eleven individual rare-earth elements (La, Ce, Pr, Nd, Sin, Eu, Gd, Tb, Ho, Er and Y) and also mischmetal at a cooling rate of 70—80℃/min. The modifier was added into the alloys by the methods of both reciprocal reaction and electrolysis of corresponding binary molten salts of rare-earth chloride and KCl. From the metallographic observation, it was shown that Eu possesses the greatest modification ability, and La the next, and both of them are permanent modifiers. The modification ability of Ce, Pr, Nd and mischmetal are even weaker than that of La. It was also found that modification ability of rare-earth elements decreases rapidly with the decreasing of their atomic radii. The greatest modification ability of Eu may be referred to the leap of its atomic radius. Owing to the similar reason, Yb (not investigated) would be expected to be the another element possessing strong modification ability in the lanthanide. In the consequence of lanthanide, from Sm to Ho the modification ability is negligible. Finally, under the conditions mentioned above, Er and Y did not show any modification effect on Al-Si eutectic alloy at all. According to the information that the atomic radius of Ac (2.03(?)) is somewhat greater than that of La (2.02A) and the modification ability may become greater in the order Y-La-Ac of the periodic table, it is deduced that the radioactive element Ac may have even greater modification ability than that of Eu. Thus the strongest modifiers would be elements La, Sr and Ac set on an oblique straight line in the periodic table. Therefore, it is assumed that the modification ability of a modifier may be the result of a certain combination of the valence electron charge number, the atomic number and the atomic radius of the modifier.