Three-dimensional analysis of eutectic grains in hypoeutectic Al-Si alloys

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. (C) 2004 Elsevier B.V. All rights reserved.

[1]  L. Arnberg,et al.  Investigation of the microstructure of the Al–Si eutectic in binary aluminium–7 wt% silicon alloys by electron backscatter diffraction (EBSD) , 2001 .

[2]  S. N. Ojha,et al.  Mushy zone morphology during directional solidification of Pb-5.8 wt pct Sb alloy , 2000 .

[3]  S. N. Ojha,et al.  Cellular/Dendritic Array Tip Morphology During Directional Solidification of Pb-5.8 Wt Pct Sb Alloy , 2017 .

[4]  Peter W Voorhees,et al.  Three-dimensional characterization of dendritic microstructures , 2001 .

[5]  K. Nogita,et al.  Eutectic Growth Mode in Strontium, Antimony and Phosphorus Modified Hypoeutectic Al-Si Foundry Alloys , 2001 .

[6]  D. StJohn,et al.  Eutectic grains in unmodified and strontium-modified hypoeutectic aluminum-silicon alloys , 2004 .

[7]  K. Nogita,et al.  Mechanisms of eutectic solidification in Al–Si alloys modified with Ba, Ca, Y and Yb , 2001 .

[8]  K. Nogita,et al.  Eutectic nucleation and growth in hypoeutectic Al-Si alloys at different strontium levels , 2001 .

[9]  K. Nogita,et al.  Determination of Eutectic Solidification Mode in Sr-modified Hypoeutectic Al-Si Alloys by EBSD , 2001 .

[10]  A. Hellawell,et al.  The mechanism of silicon modification in aluminum-silicon alloys: Impurity induced twinning , 1987 .

[11]  B. Niroumand,et al.  3D study of the structure of primary crystals in a rheocast Al–Cu alloy , 2000 .

[12]  George Spanos,et al.  Three-dimensional analysis of proeutectoid cementite precipitates , 1999 .

[13]  A. Gokhale,et al.  Application of Three-Dimensional Digital Image Processing for Reconstruction of Microstructural Volume from Serial Sections , 2000 .

[14]  M. Rappaz,et al.  About the Shape of Eutectic Grains Solidifying in a Thermal Gradient , 1994 .

[15]  P. Voorhees,et al.  The morphological evolution of dendritic microstructures during coarsening , 2006 .

[16]  M. Li,et al.  Serial Sectioning Method in the Construction of 3-D Microstructures for Particle-Reinforced MMCs , 1998 .

[17]  K. Nogita,et al.  Eutectic solidification in hypoeutectic Al–Si alloys: electron backscatter diffraction analysis , 2001 .

[18]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[19]  K. Nogita,et al.  Eutectic Solidification Mode in Sodium Modified Al-7 mass%Si-3.5 mass%Cu-0.2 mass%Mg Casting Alloys , 2001 .

[20]  P. Voorhees,et al.  Quantitative serial sectioning analysis , 2001, Journal of microscopy.