MODIFICATION OF Al-Si ALLOY

It is well known that the structures of Al-Si alloys can be modified significantly with minor additives like Na, Sr and Rare Earth (RE) metals. The operating mechanism of RE is studied through investigating its distribution and effects on Si phases. An electrolytic seperation with subsequent radioassay method and the autoradiographic technique have been developed for measuring the content and distribution of RE in alloys. The content of RE in various phases of Al-Si alloy is determined quantitatively by electrolysis of the spcimen at low temperature with subsequent radioassay. The distribution of RE in Al-Si alloy has been determined by a coating-autoradiographic technique. The morphology of Si phases which are seperated with electrolysis method are observed using SEM. The results show that the modifier in Si phases is much higher that that in alpha-Al phases. The microdistribution of modifier is few in primary alpha Al and primary Si, but abundant in eutectic colony (eutectic Si and eutectic Al). It is hence concluded that RE is primarily concentrated in eutectic Si phase. Eutectic Si phase containg a certain amount of modifier has a fibrous morphology.

Modifier (RE) Contents (Radioassay) in Si and Al Phases in Al-13wt%Si Alloy


Modifier (RE) Distribution (Autoradiograph) in Al-13wt%Si-0.16wt%RE Alloy

(a) Emulsion film photograph and (b) Optical metallograph

Modified Morphology of Eutectic Si in Al-13wt%Si Alloy

(a) 0.16wt%RE; (b)0.32wt%RE and (c) 0.37wt%RE


RELATED PUBLICATIONS

1. P. Dang, Q. Han and W. Du, "Microdistribution and Function of Rare Earth Metals in Al-Si Alloys", Proceedings of the Second International Conference on Rare Earth Development and Application (English), Beijing, China, May 27-31, 1991. International Academic Publishers, Vol. 1, 317.

2. P. Dang, W. Du and Q. Han, "Electrolytic Extraction and Radioactive Measurement of Cerium Contents in Various Phases of Al-Si Alloys", Rare Metals, 246, No.3, 13 (1989).

3. W. Du, P. Dang, Z. Cao and Q. Jiang, "Influence of Modifiers on the Nucleation and Growth of Silicon Phases in Al-Si Alloys", Proceedings of the First International Conference on W-Ti-RE-Sb (English), Changsha, China. International Academic Publishers, 1251, Vol.2 (1988).

4. P. Dang, W. Du, Q. Jiang and Q. Han, "A TEM Study on the Orientation Relationships between Eutectic Si and Eutectic alpha-Al phases in Al-Si Eutectic Alloys", Journal of Rare Earths, 41, No.4, 6 (1988).

5. W. Du, P. Dang and Q. Han, "Autoradiography Study on the Inhomogeneity of Trace Modifier in Al-Si Alloys", Journal of Rare Earths, 59, No.3, 6 (1988).

6. P. Dang, W. Du and Q. Han, "Study on the Iron-contained Impurities in Casting Al-Si Alloys", Rare Earths, 43, No.1, 9 (1988).

7. P. Dang , Q. Jiang, W. Du and Q. Han, "Combined Ce and P Modifications of Al- 20%Si Alloys", Rare Earths, 22, No.6, 8 (1987).

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