Development Of Planar Flow Casting Atomization Process For Production Of Sn-Cu Alloy Powders

The powder making technology of planar flow casting atomization process was further studied in this thesis. With the self-made equipment of planar flow casting atomization process, Sn99.3Cu0.7 alloy powders were produced. And the size distribution and microstructures of Sn99.3Cu0.7 alloy powders produced were investigated.The morphology and microstructures of Sn99.3Cu0.7 powders were studied. The results indicated that the morphology of the powders was made up of strips, spherules, and a few powders were in the shape of flakes. With the decrease of powder diameter, the morphology of the powder became more and more round, and the surface of powder became smoother and smoother. The microstructure of Sn99.3Cu0.7 alloy powder was composed ofβ-Sn and lamellar eutecticη'+β.The great supercooling of the alloy powder was investigated by the DTA method. The experimental results showed that the supercooling of Sn99.3Cu0.7 alloy powder which were in the size of 48 and 98 micron were 88.73℃and 52.21℃, respectively. When the powder is produced by the planar flow casting atomization processs, the supercooling will be much bigger, and the supercooling will be bigger and bigger when decreasing the powder dimensions.Finally, numerical simulation was carried out for the formation stage of the metal powder. The diameter, velocity and temperature of metal droplets disintegrated were calculated through numerical computation, and the effects of main technological parameters on droplet diameters were emphatically analyzed. At the stage of metal droplet flight and solidification, the relationships among the flight distance, velocity and flight time of metal droplet were formulated. The cooling and solidification behavior of metal droplet in fight in the atomization box consecutively undergoes five different thermal regions, i.e. liquid phase cooling, nucleation and recalescence, melt solidification, eutectic solidification and solid phase cooling. And the variations of droplet velocity, Reynolds number, heat transfer coefficient, flight time, droplet temperature, solid fraction and cooling rate of metal droplets with flight distance were computed. Furthermore, the effects of wheel speed, gas density and droplet superheating on the flight and heat transfer behaviors of metal droplets were discussed.