Process optimization of porous Al2O3 filter via layered extrusion forming

Porous ceramic filters have great potential in alloy casting fields to reduce casting defects such as reoxidation inclusions and pores. However, the uniform shape and size distribution is critically restricted by the conventional manufacturing process. Herein, an additive manufacturing method, layered extrusion forming, was applied for rapidly preparing porous Al2O3 ceramic filters with controllable pores morphology and overall application performance, including the flexural strength and total porosity. This paper firstly investigated the characteristics of the extruded filaments, then optimized the process parameters (the filling rate, extrusion nozzle diameter, and filling angle) of layered extrusion forming through an orthogonal experiment and a response surface analysis. Finally, based on the flexural strength, total porosity, and linear shrinkage, the optimum sintering temperature was determined to achieve the proper formation of porous Al2O3 ceramic filters with adequate strength and porosity properties. Results show that when prepared at the 20% filling rate, the 0.34 mm extrusion nozzle diameter, the 0/90/45/-45 degrees filling angle, and sintered at 1400 degrees C, the porous Al2O3 ceramic filter sample possesses excellent comprehensive performance. Under the optimized parameters, the flexural strength 14.35MPa, the total porosity is 67.6%, the macroscopic porosity is 53.40%, and the linear shrinkage rate is 2.51%.