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| THE MODIFICATION OF Si PHASE IN A1-Si EUTECTIC ALLOYS(Ⅱ)——Relationship between Unequilibrium Degree of Si Phase and its Appearance |
| by ZHANG Qiyun; LIU Shuqi; HU Jia (Dept. of Chemistry; Peking University)(Manuscript received 1 September; 1982; revised manuscript 23 August; 1983) |
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Cite this article:
by ZHANG Qiyun; LIU Shuqi; HU Jia (Dept. of Chemistry; Peking University)(Manuscript received 1 September; 1982; revised manuscript 23 August; 1983). THE MODIFICATION OF Si PHASE IN A1-Si EUTECTIC ALLOYS(Ⅱ)——Relationship between Unequilibrium Degree of Si Phase and its Appearance. Acta Metall Sin, 1984, 20(2): 138-218.
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Abstract A comparison study has been made of the modification of Al-Si eutectic alloys with modifiers Na, Sr and La by metallography and SEM. It has been found that the concentrations of just entire modification of the modifiers in eutectic alloys were aU about 0.03 at.-％. It shows that the modification is influenced directly by the number of modifier atoms rather than weight. In SEM study, the Si phase was extracted out from the eutectics with HCl+ H_2O_2 followed by dil. HCl wash. Detailed observation found that the appearance of Si fibres at entire modification were something different with various modifiers used, the shortest were the crystals modified with La, Sr the next, and that of Na-modified were longer. This phenomenon was regarded as by the influence of valence electron charges of different modifiers. The SEM observation of annealed Si extracted from eutectic bulks found that the eutectic Si phase gradually dissolved in α-Al phase while new ball form equilibrium crystals grew up. The dissolve speed of Si phase dicreased with the modifier order La, Sr, Na. No evidence was found about the dissolve of primary Si phase even annealed over 144 h. It has suggested that the modified Si phase is in unequilibrium, the higher the valence electron charges of the modifiers the more unequilibrium of the Si crystals will be. The primary Si closed to the equilibrium state which therefore can not be modified in general situation.
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Received: 18 February 1984
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2 郑朝贵;姚连克;张启运,金属学报,18(1982) ,661．
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5 张启运;刘淑祺;樊晓红,金属学报,18(1982) ,581． |
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