| Spray forming involves sequential stages of the melt atomization, the droplet quench, the droplet consolidation on collision and the preforms cooling in continued processing step. These sequential stages control and change the solidification conditions of the melt and determine the spray formed performs microstructure. Near-net-shape manufacturing is another characteristic of the spray forming. The preforms shape depends on the structure and amount of the atomizator, the shape and movement of the substrate. Materials microstructure and shape of the spray formed preforms is influenced by many factors. However, the effects of the processing parameters have not been made clear yet. So it is still necessary to research the spray forming process by experimental and numerical simulation.In this paper, the effects of processing parameters on the billet microstructure and shape of the the hypereutectic Al-Si alloy are studied and analyzed by computer simulation and experiments. Main results are summarized as follows:Based on the heat transfer analysis of the droplet, the cellular automaton model was used to simulate the shape, size and distribution of the primary Si microstructure in the droplet. The influence of the initial gas velocity and the melt temperature to droplet size, temperature and fractional solidification was computed. The size and the structure of the primary Si in the cooling droplet before collision with the substrate is also calculated. Based on the experimental micrographic studies, the forming and transition of billet microstructure is analyzed. It is concluded that the droplets size and distribution, the rapid solidfication of the droplets are the conclusive factors to determine the microstructure of spray formed billets. During the rappid cooling of the droplets before collision with substrate, a nonequilibrium structure of the droplet is formed. This structure is reconstructed in the half-solid solidification process of the droplet collision with the substrate. The resulted is a fine equiaxed grain structure.Contour line modeling was established based on a suited coordinate systems. The releation of deposition position and withdrawal velocity of substrate was obtain by calculating the droplet flow rate in space. The steady deposition position and optimum withdrawal velocity of substrate was ascertained by analyzing the influence of substrate position and withdrawal velocity to the rod billet surface shape. The modeling is also used to analyze the growth mechanism and the influence of several important processing parameters, e.g., the initial spray angle, the mass distribution of the spray cone, the atomizator position and the withdrawal velocity of the substrate on the rod billet surface shape. A rod billet shape modeling, in which a improvement approach for the calculation of the shadowing efficiency is constructed, is built up to predict the shape evolution of a growing rod billet using the coordinate tracking method. On the basis on the numerical simulation results, a route for the optimization of spray forming parameters is presented. The hypereutectic Al-Si alloy rod-billets with the desired shape and dimension are manufactured by using the optimized processing parameters. These show that the models can predict the spray forming process well and provide good guidance for the optimization of the processing parameters.The AlSiFeCuX(X=Mg, La, Ce) were fabricated using the optimization parameters, which containing 30wt%Si with an excellent combination of low coefficient of thermal expansion and good wear resistance. The relative density and the grain size of the preforms are about 95% and 5-20μm, respectively. After the subsequent hot extrusion and T5 heat treatment, the thermal expansion coefficient of AlSiFeCuMg, AlSiFeCuCe and AlSiFeCuLa are 15.3×l0-6℃-1,16.5×10-6℃-1, 16.0×10-6℃-1 respectively. The essential wear testing was examined to spray fomed materials.
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