P/M composites of Al-Si-Fe-Cu alloy with SiC particles hot-extruded after preliminary compaction
Marek Wojtaszek
Quarterly No. 4, 2011 pages 336-341
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abstract The objective of the research work was to evaluate the possibility of forming high quality composites based on the Al17Si5Fe3Cu1.1Mg0.6Zr alloy, reinforced with silicon carbide particles, by means of preliminary hot compaction and hot extrusion processes. The mixtures were prepared with a matrix alloy powder and reinforcing phase, with a volume fraction of SiC particles maintained at 5, 10 and 15%. The feedstock to be extruded was prepared by preliminary hot compaction of the powders and composite mixtures. Subsequently, the semi-finished products were subjected to forward extrusion in isothermal conditions. For the obtained materials, both after compaction and after extrusion, their relative densities and hardness were determined. For the extruded materials, their compressive strength was determined, stress-strain curves were constructed, and their microstructure was analysed as well. The obtained materials showed high relative density and mechanical properties depending on the amount of deformation and volume fraction of the reinforcing phase. As a result of introducing SiC particles into the matrix or increasing their volume fraction, an increase of hardness was observed. Hot extrusion resulted in decreased hardness as compared to the material after preliminary compaction. With a volume fraction of SiC maintained not higher than 10%, the compressive strength of the extruded materials increased, while at 15% the average compressive strength was lower when compared to the matrix alloy. Based on room temperature stress-strain curves it was found that introducing particles into the matrix or increasing their volume fraction caused a decrease of the strain level at which failure of the specimen occurred. Increasing the volume fraction of SiC particles up to 10% resulted in a strengthening of the matrix, while in the case of a composite containing 15% of particles, a lowering of strength was observed. Specimens subjected to compression at a temperature of 200°C were deformed plastically, and the stress value at which the deformation occurred increased with an increasing volume fraction of the reinforcing phase. The microstructure of the matrix obtained as a result of extrusion realized with the assumed parameters was fine-grained. In the case of composites, the observations revealed a uniform distribution of SiC particles in the matrix. Based on the obtained results of the investigations, it was concluded that in the case of products formed with the assumed parameters, the introduction of SiC particles into the matrix, with a volume fraction maintained not higher than 10%, has a favourable effect, while at 15% a decrease of the analysed material properties at room temperature and their increase at an elevated temperature is observed. The obtained results of investigations allow us to conclude that the decision to introduce SiC particles into the Al17Si5Fe3Cu1.1Mg0.6Zr alloy matrix as a reinforcing phase, as well as of their volume fraction, should depend on the foreseen working conditions of the element made of this material.