Aluminum matrix composites reinforced with SiC and AlN particles were prepared by powder metallurgy methods. The microstructures were observed by optical microscope(OM), scanning electron microscope(SEM) and transmission electron microscope(TEM). Microyield strength was measured by continuous loading method to assess the dimensional stability of the composites. The stabilizing processes of 35%SiCp/2024Al were studied followed by researching on the effects of different particles and various volume fractions reinforcements on the dimensional stability of the composites. The residual stress alternations in the composites during quenching and thermal cycling treatment were analyzed by finite element method at the last part of this paper.
The microstructures of the composites showed that the reinforcements and matrix alloy combined well and the interfaces were clear, without any reaction products. The microscopy also exhibited that high density dislocations were discovered in the matrix adjacent to the interface with the particle, especially in the regions near to the sharp tips of the reinforcements.
The results of the thermal cycling process indicated that the contribution of the treatment could be extended by increasing thermal cycling times, expanding holding time or lower holding temperature. The highest microyield strength of the composites was achieved after aging at 180℃ for 8 hours and the values decreased quickly with the increasing of holding time.
Composites reinforced with AlN particles possess better dimensional stability compared with these reinforced with SiC particles in this article for the reason that smaller and round particles generated lower density dislocation and stress in the matrix when the composite experience the same thermal process. The composite included higher volume fraction AlN particles exhibited higher microyield strength but lower macroyield strength compared with these contained lower volume fraction inclusions.
The outcomes of the finite element analysis displayed deep cooling process could efficiently reduce the large local stress generated during the quenching; both to the composites reinforced with irregular and near round particles. But only the stress near the particle tips of the silicon carbide reinforcements relaxed in the further thermal cold cycling treatment according to the results of finite element analysis.
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