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Evolution of Solidification Microstructure of High Purity Al-Si Alloys during Heat Treatment

Author: SuZuoZuo
Tutor: ZuoLiang；YuFuXiao
School: Northeastern University
Course: Materials Science
Keywords: High purity Al-Si alloy Modification Heat treatment Equiaxed grains
CLC: TG166
Type: Master's thesis
Year: 2008
Downloads: 119
Quote: 0
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Abstract


Pre-heat treatment prior to the deformation of the cast structure continuous the brittle fiber mesh of silicon phase change for the dispersion of granular aluminum-silicon alloy to achieve deformation premise, our group has been observed to semi-continuous casting Al-Si alloys in heat treatment and hot deformation process accompanied silicon phase particles of the same time, the aluminum matrix appears equiaxed grain equiaxed formed respectively to any contact with the heating and deformation processes. In addition, this phenomenon may be solidified in the process of forming eutectics and alloys in correlation. In this study, using optical microscopy, scanning electron microscopy and electron backscatter diffraction attachments analytical tools, modification and non-modification of high purity hypoeutectic the Al-7Si and a eutectic of Al-12.7Si alloy prepared by slow cooling of different solidification conditions the nucleation temperature and solidification research organizations conduct research and the preparation of alloy microstructure evolution during heat treatment characteristics. The main conclusions are as follows: 1. From cooling curve eigenvalue and not judge Alloys situation good or bad, just after the deterioration of the alloy eutectic growth temperature decreased more unmetamorphosed. When adding the Sr content of not less than 110ppm, Al-7Si alloy can be achieved by good modification effect; When adding Sr content of not less than 220ppm, Al-12.7Si alloy can reach a good modification effect. 2. Of different metamorphic situation Al-7Si, and Al-12.7Si alloy in after 500 ° C different incubation time heat treatment, the eutectic silicon fuse and granulated, does not appear roughened. After incubated for 6 hours, without a modification treatment of the alloy in the majority of the eutectic silicon morphology was still short rod, a small amount occur neutropenia, granulating ineffective; metamorphic good alloy After incubated for 6 hours, to achieve better the granulation effect, the size in the 2-3μm. 3 eutectic silicon phase granulated, under an optical microscope were observed to aluminum eutectic phase appears clear grain boundary of crystal grains, but did not appear in the α (Al) on the dendrites. Eutectic silicon particles in aluminum matrix on the distribution of more intensive, the grain distribution in this region will be more intensive and more small size. For unmetamorphosed alloy, grain, roundness is not high, in the 10-30μm size range; metamorphic good alloy grain almost equiaxed size in the range of 3-8μm. Modification alloy eutectic aluminum phase heating process of organizational change, confirmed by chilling deterioration and chemical deterioration aluminum-silicon alloy in the heating process of grain structure evolution of the common law. EBSD study confirmed modification alloy eutectic region forming the refined equiaxed grain boundaries are small angle grain boundaries.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Heat treatment > The heat treatment of non-ferrous metals and their alloys
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