Materials Transactions Online

Materials Transactions, Vol.58 No.05 (2017) pp.734-738
© 2017 The Japan Institute of Metals and Materials

Effect of TiB2 on Microstructure of 7075 Al Alloy Semi-Solid Slurry at Different Solid Fraction

Guisheng Gan1, 2, Chunhong Zhang1, Donghua Yang1, Mingbo Yang1, Xin Jiang1 and Yun-long Shi1

1Chongqing Municipal Engineering Research Center of Institutions of Higher Education for Special Welding Materials and Technology (Chongqing University of Technology), Chongqing 400054, China
2College of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

TiB2/7075 Al matrix composites were fabricated by in situ reaction, and the effect of TiB2 particle content on the microstructure of 7075 Al alloy slurry in semi-solid state at different solid fraction were investigated. The results showed that the grain sizes of TiB2/7075 Al matrix composites firstly decreased then increased and finally decreased again with the increase of TiB2 content because the role of particles shifted from dominating by locating to dominating by nucleation as the quantity of TiB2 particles increased due to the decrease of the mean diameter of TiB2 particles. As the holding time increasing in the semisolid state, dendritic grains were necked and remelted at first, then rosette grains melted and shrank into the globular grain, finally the globular grains began to grow, but the number of grains decreased and their mean grain size increased. The minimum grain size of 3.0, 4.5 and 9.0%TiB2/7075 Al matrix composites slurry were 81 μm, 51 μm and 69 μm after holding for 35, 20 and 50 mins at 630℃, respectively. The minimum grain size of 3.0 and 4.5%TiB2/7075 Al matrix composites slurry were 100 μm and 75 μm after holding for 120 and 90 mins at 620℃, respectively. However, the maximum size of globular grains was not associated with the TiB2 particle content, the maximum grain sizes of 3.0%TiB2/7075 and 4.5%TiB2/7075 Al matrix composites slurry at 620℃ were approximately 128 μm.

[doi:10.2320/matertrans.M2016458]

(Received 2016/12/26; Accepted 2017/02/15; Published 2017/04/25)

Keywords: 7075 aluminium alloy, semi-solid, TiB2 particles, solid fraction, thixoforming

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