Threedimensional analysis of eutectic grains in ...（共晶颗粒的三维分析u2026u2026）.pdf

Materials Science and Engineering A 392 (2005) 440–448 Three-dimensional analysis of eutectic grains in hypoeutectic Al–Si alloys Cameron M. Dinnis, Arne K. Dahle∗, John A. Taylor CRC for Cast Metals Manufacturing (CAST), Division of Materials Engineering, School of Engineering, The University of Queensland, UDP Number 055, St. Lucia, Qld 4072, Australia Abstract An approach to the qualitative analysis of quenched microstructures in three dimensions is presented and demonstrated on unmodified and Sr-modified Al–10% Si samples. The samples were repeatedly polished to obtain a series of digital images through the depth of the microstructure. A three-dimensional reconstruction of the microstructure was obtained by assembling the images of the serial sections. Reconstructions were made of unmodified and Sr-modified Al–Si eutectic grains that were quenched during eutectic solidification. The three- dimensional reconstructions show that strontium modification changes the size and morphology of the Al–Si eutectic grains. Sr-modified eutectic grains are large approximately spherical grains and grow with a high interface velocity. In the unmodified alloy, many small eutectic grains grow from the dendrite arm tips. The unmodified eutectic grains appear to grow from the dendrite tips into the undercooled liquid, rather than back-filling the dendrite envelope, possibly continuing to grow in the same manner as the equiaxed dendrites. © 2004 Elsevier B.V. All rights reserved. Keywords: Aluminium alloy; Serial sectioning; Al–Si eutectic 1. Introduction generally been observed with the aid of deep etching and