Journal of Materials Research

Articles

Origin of the anomalous volume expansion in Al–Si alloys above liquidus

W. M. Wanga1 c1, X. F. Biana2, H. R. Wanga2, Zhen Wanga2, L. Zhanga3, Z. G. Liua3 and J-M. Liua3

a1 Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, People's Republic of China; and Key Laboratory of Liquid Structure and Heredity of Materials, Shandong University, Jinan 250061, People's Republic of China

a2 Key Laboratory of Liquid Structure and Heredity of Materials, Shandong University, Jinan 250061, People's Republic of China

a3 Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, People's Republic of China

Abstract

The sessile-drop method and high-temperature small-angle x-ray diffraction technique were used to characterize the density of liquid Al–Si alloys with Si content C = 0 to 22 wt%. A distinct abnormal volume expansion of the hyper-eutectic melts was identified just above the liquidus (within TLTk) during the heating sequence (h.s.), which is irreversible during the cooling sequence (c.s.). This phenomenon is explained by the segregation of Si atoms from the supersaturated “quasi-eutectic” structure and formation of silicon clusters in the superheated melt. In addition, a pre-peak in the x-ray diffraction spectrum of Al–14% Si melt was observed at 850 °C, which is associated with the silicon clusters. The pre-peak remains when the superheated melt is cooled down to the liquidus (670 °C); this result is in accord with the density measurements.

(Received March 09 2001)

(Accepted October 01 2001)

Correspondence:

c1 Address all correspondence to this author. e-mail: wmwang@nju.edu.cn

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