ã€ALUMINIUM NETWORK】ALUMINUM MATRIX COMPOSITE MATERIALS ARE NON-HOMOGENIC MIXTURES OF METAL NON-METALLIC PARTICLES, WHISKERS, OR FIBERS AS THE MATRIX AND METAL ALUMINUM AND ITS ALLOYS AS THE MATRIX AND ARE ENRICHED IN AEROSPACE, AUTOMOTIVE INDUSTRY Applications. Since the powder metallurgy method can be used to add the reinforcements to the composite matrix in any ratio, the reinforcements are also easy to form a more uniform distribution on the macroscopic, and the sintering temperature is low, the interface reaction is easy to control; at the same time, the material properties and stability Obviously better than other materials prepared by other methods, so the powder metallurgy method has become a common process for preparing aluminum matrix composites.
The specific process for preparing a composite material by powder metallurgy includes the following steps.
one. Mix powder.
General mixing methods include ordinary dry mixing, ball milling and wet mixing. Among these three mixed powders, ordinary dry blending and wet blending are prone to phenomena such as uneven distribution of reinforcements and a large number of agglomerations, delaminations, etc., which are usually common and effective in ball milling.
two. Powder preloading.
After powder mixing is completed, powder preloading is performed. Powder precompression molding methods mainly include cold pressing and cold isostatic pressing. In contrast, cold pressing is a more economical and commonly used powder prepressing method. After pre-compression of the aluminum alloy powder, it is generally required that the preform density be 70% to 80% of the density of the composite material in order to facilitate gas evolution during the degassing stage. Since the aluminum powder and the reinforcement body easily adsorb water vapor and oxidize, the powder green body releases a large amount of water vapor, hydrogen gas, carbon dioxide, and carbon monoxide gas during the heating process. Therefore, the green body should be degassed prior to thermal processing to avoid bubbles and cracks in the product; the degassing temperature should generally be equal to or slightly higher than the subsequent hot-pressing, hot-work deformation and heat treatment temperatures to avoid remnants in the compact. The water and gas cause bubbles and delamination in the material. However, if the temperature is too high, some other elements in the aluminum alloy may be burned, and the intermetallic compounds that play a reinforcing role in the alloy will be aggregated and coarsened, and the properties of the material will be reduced.
three. Curing.
After degassing the powder, it is densified, ie sintered, hot pressed, hot isostatically pressed and hot extruded loose powder or pre-compressed powder. In the case of ensuring low cost and high productivity, the blank is extruded through a single-axis cold extrusion, after degassing, it is heated to a certain temperature at a certain rate, and hot extrusion is performed according to a certain extrusion ratio, and then the later Heat treatment to get the final material. This powder forming process, which combines powder metallurgy with subsequent densification (eg, extrusion, rolling, etc.), enables the powder to plastically deform under short-time high temperature and high pressure, thereby achieving the bond between powder particles. This kind of technology is used in the research of powder metallurgy to prepare aluminum matrix composites. Compared with the conventional powder metallurgy method, in addition to the three-dimensional compressive stress of the powder particles in the extrusion process, they also bear a large shear force along the extrusion direction, and the oxide film on the surface of the powder particles further strengthens the adjacent powder particles. With the strength of bonding, the microstructure is small and uniform, and there is little segregation of components. There is no obvious agglomeration of reinforcement particles, which is beneficial to the distribution in the matrix. In addition, this method does not require sintering, which reduces the preparation process and reduces the cost. Compared with the high-cost hot isostatic pressing process, the comprehensive advantages of powder hot extrusion process are more obvious, and materials with excellent physical and mechanical properties can be directly obtained. (Steel Research)
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