Influence of size of sic particles on selected properties of aluminium-based composites obtained by extrusion of P/M compacts
Marek Wojtaszek
Quarterly No. 4, 2011 pages 331-335
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abstract The results of investigations are presented, which are aimed at determining the effect of the size of SiC particles on selected properties of aluminium-based composites. As initial materials, atomized aluminium powder and silicon carbide powders of different particle size were applied. The scope of the research included the preparation of a matrix and composite material samples, as well as the determination of their selected properties. Powder metallurgy and plastic working technologies were applied to obtain the composite materials. The volume fraction of the reinforcing phase particles in the matrix was set constant at the level of 10%. All the samples were formed using the same parameters. The manufacturing process included the mixing of the components, cold compaction of the aluminium powder and mixtures as well as hot forward extrusion of the P/M compacts. Based on extrusion force measurements, it was shown that introducing smaller silicon carbide particles into the matrix resulted in the necessity to apply a higher load. For extruded materials, their relative density, hardness and abrasion resistance were determined. The results obtained from compression tests performed at room temperature and at 200°C allowed us to construct flow curves for the investigated materials. Microstructure examination was also performed. It was shown that application of the proposed forming technology results in obtaining products showing a relative density close to that of a solid material. The introduction of silicon carbide particles into the matrix caused an increase of true stresses at which deformation proceeded, regardless of the test temperature. In the case of compression of the samples performed at 200°C, the increase of stresses was observed as a result of a reduction of the reinforcing phase particles size in the matrix. In case of compression tests performed at room temperature, no unequivocal influence of particle size on the character of the obtained curves was observed. The realized microstructure examination revealed uniform distribution of SiC particles in the aluminium matrix. The particles were closely adherent to the matrix, and the metallographic specimens did not reveal any voids caused by particles falling out during specimen preparation. The comparative abrasion test showed that the introduction of 10% SiC particles into the matrix and increasing their size, with their volume fraction held constant, leads to lower abrasive wear of the investigated materials. Based on the obtained results, it was concluded that in the case of the given components and their forming technology, the introduction of particles into the matrix has a favourable effect, while their size influences individual properties differently. Therefore, the final selection of the proper size of silicon carbide particles applied as reinforcement in the aluminium matrix, should be based on the knowledge of the characteristic and working conditions of the composite product, as well as the expectations to be met.