Particle Size Dependence of MnO Reduction for Fabrication of Al-AlMnOX Composite vir Stir Casting
In the present work, a composite of Al matrix reinforced with 10% MnO particles has been developed using stir casting technique. MnO with particles size of range of 53 to 90 μm for composite (A) and 188 to 250 μm for composite (B) as reinforcement and pure Mg powder as wetting agent to improve the wettability of MnO particulates with molten Al were used for production of Al-MnO composites having 10 wt.% of MnO. The pouring temperature and stirring speed have been set to 750 ̊ C and 900 RPM, respectively. The main purpose of this work is to study the dependence of MnO reduction on particle size for fabrication of Al matrix composite via stir casting route. For structural analysis, fundamental material characterization like SEM, EDX, XRD and OM was carried out for developed composite samples. The results reveal that an in-situ formed finer alumina (Al2O3) particles and an intermetallic precipitate of Al-Mn as a result of chemical reaction between molten Al and MnO particles have been observed using SEM with EDX of both developed composite samples. SEM with EDX analysis has detected that the composition of reinforcement particles of composite sample of A contains Al and O, which indicates presence of in-situ generated Al2O3. While the composition of reinforcement particles of composite samples of B contains high percentage of Mn, high percentage of O and low percentage of Al, which indicates presence of unreacted MnO and generated in-situ Al2O3 to form in-situ (AlMnOx) intermediate compound. This has been also confirmed by elemental mapping SEM analysis. SEM analysis of in-situ AlMnOx particles at high magnification has detected that their structure is porous. Optical micrographs have shown that a good bonding between particles and the matrix in both developed composite samples with presence some aggregations of particles and pores. For both developed composite samples, the amount of (Al-Mn) phases formed in the specimens may be too little to be detected directly from the bulk specimens by XRD. Phase identification by X-ray diffraction technique verifies of presence Al and Al2O3 phases in composite sample of A, while it verifies of presence Al and MnO phases in composite sample of B.
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