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Materials (Basel). 2017 Feb 4;10(2). pii: E132. doi: 10.3390/ma10020132.

Refining Mechanism of 7075 Al Alloy by In-Situ TiB₂ Particles.

Author information

1
Chongqing Municipal Engineering Research Center of Institutions of Higher Education for Special Welding Materials and Technology, Chongqing University of Technology, Chongqing 400054, China. ggs@cqut.edu.cn.
2
College of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China. ggs@cqut.edu.cn.
3
Collaborative Innovation Center of Steel Technology, University of Science & Technology Beijing, Beijing 100083, China. byang@ustb.edu.cn.
4
Chongqing Municipal Engineering Research Center of Institutions of Higher Education for Special Welding Materials and Technology, Chongqing University of Technology, Chongqing 400054, China. baiguozhenke@163.com.
5
Chongqing Municipal Engineering Research Center of Institutions of Higher Education for Special Welding Materials and Technology, Chongqing University of Technology, Chongqing 400054, China. jiangxin@163.com.
6
Chongqing Municipal Engineering Research Center of Institutions of Higher Education for Special Welding Materials and Technology, Chongqing University of Technology, Chongqing 400054, China. 18324133469@163.com.
7
College of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China. ypwu@mail.hust.edu.cn.

Abstract

The nucleation undercooling of TiB₂/7075 Al matrix composites, the microstructure observed after solidification at different cooling rate, and the size and distribution of TiB₂ particles were investigated. The experimental results have shown that the grain sizes of TiB₂/7075 Al matrix composites firstly decreased, then increased, and finally decreased again with the increase of TiB₂ content. The nucleation undercooling of TiB₂/7075 Al matrix composites first increased, then decreased, and finally increased again with the increase of TiB₂ content when the cooling rates was 5 and 10 °C/min respectively, but kept decreasing with the increase of TiB₂ content at a cooling rate of 20 °C/min. The melting and solidification process showed no significant change with the decrease of cooling rate in 9.0% TiB₂/7075 Al matrix composites. Most small particles can act as heterogeneous nucleus, which induced grain growth and were captured into the grain by the solid/liquid interface. At the same time, most of the larger particles and a minority of the small TiB₂ particles are pushed into the grain boundary; locating in the grain boundary can hinder the Al atoms from diffusing during the solidification process and restrain α-Al phase growth. The influence of particles shifted from dominating by locating to dominating by nucleation as the quantity of TiB₂ particles increased.

KEYWORDS:

TiB2 particles; composites; microstructure; nucleation undercooling

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