Influence of Dispersed Solid Particles on the Liquid-Liquid Separation Process of Al-Bi Alloys
Lin ZHANG,Tiannan MAN,Engang WANG()
Key Laboratory of Electromagnetic Processing of Materials Ministry of Education, Northeastern University, Shenyang 110819, China
Cite this article:
Lin ZHANG,Tiannan MAN,Engang WANG. Influence of Dispersed Solid Particles on the Liquid-Liquid Separation Process of Al-Bi Alloys. Acta Metall Sin, 2019, 55(3): 399-409.
Al-Bi alloy is a kind of bearing material with self-lubricating performance. Whereas, in such immiscible alloys macrosegregation occurs generally due to the miscibility gap in solidification process. This study is designed to produce CeBi2 compound particles in Al-Bi melt through the addition of rare earth element Ce. The solidification experiment is processed with liquid quenching and natural cooling respectively, and the effect of dispersive solid particles on liquid-liquid separation is compared at different cooling rate. The dispersive solid particles act as nucleation site and improve the nucleation rate of Bi-rich droplets in liquid-liquid solidification, leading to the size refinement and dispersive distribution of Bi-rich phase, which promote the bearing performance of Al-Bi alloy. The behavior of Bi-rich droplets is simulated by using of discrete multi-particle approach, considering the movement, growth and collision. The results show that Stokes motion is the main cause of macrosegregation, and the natural convection affects the distribution of droplets. The natural convection prolongs the suspension time of droplets, and reduces the macrosegregation. In the case of Ce addition, CeBi2 acts as nucleation site to enhance the amount of Bi-rich particles in each time step of simulation and refine the droplet size, which lead to a reduction of macrosegregation. Compared with the Ce free specimens, Al-Bi-Ce alloy has a slower segregation rate and relatively less macrosegregation. Both the simulation and experiment results show a multimodal particle size distribution, and their peak value decrease with increasing particle size. The simulated results is in good accordance with the experiment.
Fund: National Natural Science Foundation of China(51674083);National Natural Science Foundation of China(50901019);Programme of Introducing Talents of Discipline to Universities(B07015)
Fig.1 Microstructures of Al-Bi (a, c) and Al-Bi-Ce (b, d) alloys after liquid quenching (a, b) and natural cooling (c, d)
Fig.2 Size distributions of the dispersed droplets in Al-Bi (a) and Al-Bi-Ce (b) alloys after liquid quenching (The bars represent the counts of droplets in the cross-section region of 1 mm2, and the dotted lines represent the log-normal distribution of probability density)
Fig.3 SEM image (a) and EDS analyses (b) of Al-Bi-Ce alloy
Fig.4 Coefficient of friction (a) and wear rate (b) as a function of sliding distance in Al-Bi and Al-Bi-Ce alloys
Fig.5 The temperature field (a) and flow velocity field (b) in model
Fig.6 Spatial microstructure evolutions in Al-Bi alloys (a~e) and Al-Bi-Ce alloys (f~j) at time of 0 s (a, f), 0.5 s (b, g), 1 s (c, h), 2 s (d, i), 3 s (e, j)
Fig.7 Average radius and number of droplets in Al-Bi and Al-Bi-Ce alloys as a function of time
Fig.8 Evolution of a droplet radius distribution with time for Al-Bi (a) and Al-Bi-Ce (b) alloys
Fig.9 Comparison of radius distribution between inner part and outer part in Al-Bi, 2 s (a) and Al-Bi-Ce, 2.5 s (b) alloys
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