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

Guisheng Gan,Bo Zhang,Bin Yang,Xin Jiang,Yiping Wu,Yunlong Shi

doi:10.3390/ma10020132

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.

Highlights

TiB2 particles can improve the strength and modulus of aluminum alloy due to high hardness and modulus, and have been widely used in aluminum alloy as reinforcement and grain refiner, especially in the aeronautical industry as structural materials [1,2,3,4,5]
Greer et al investigated the effects of the hypothetical size distributions of TiB2 particles on as-cast grain size in Al alloys, and found that
The liquidus liquidus and solidus temperatures of composites were measured by NETZSCH Q100 differential and solidus temperatures of composites were measured by NETZSCH Q100 differential scanning scanning calorimetry (DSC) with weight of about 8–9 mg, and the heating and cooling rates were 1 calorimetry (DSC) with weight of about 8–9 mg, and the heating and cooling rates were 1 and and 5, 10 and 20 °C/min between 400 °C and 700 °C, respectively

Summary

Introduction

TiB2 particles can improve the strength and modulus of aluminum alloy due to high hardness and modulus, and have been widely used in aluminum alloy as reinforcement and grain refiner, especially in the aeronautical industry as structural materials [1,2,3,4,5]. Greer et al investigated the effects of the hypothetical size distributions of TiB2 particles on as-cast grain size in Al alloys, and found that. The particle density and the nucleation undercooling of the refining particles two main undercooling parameters toofcontrol the excellent grain refiner [18,19,20]. The particle density andwere the nucleation the refining transition to equiaxed growth. The matrix composites by using scanning calorimetry (DSC), compare to the microstructure nucleation undercooling of TiBdifferential. Al matrix composites by using differential scanning calorimetry after compare solidification, investigate the size and and distribution of TiB2 the particles. The (DSC), to the and microstructure after solidification, investigate size and distribution refining mechanism of the composites is discussed.

Experimental

Results and Discussion

The grain sizes107 of of mean grainwith sizesaofcooling

Effect of TiB2 Content on the Nucleation of 7075 Al Alloy

Conclusions