Fabrication and mechanical behaviour of aluminum matrix composite materials.

摘要

Aluminum matrix composite materials containing SiC whisker and Saffil alumina short fiber are fabricated by the squeeze casting method. It is demonstrated that the direct squeeze infiltration method is suitable for discontinuously reinforced metal matrix composites (discontinuous MMCs) whose volume fractions are in the range of 0.15-0.3; squeeze casting of compounds for the fabrication of discontinuous MMCs with less volume fractions ({dollar}<{dollar}0.1).; Mechanical properties, such as Young's modulus and ultimate tensile strength, are improved up to 80% by the addition of reinforcement. However, strength at 300{dollar}spcirc{dollar}C maintain their 70% of strength at room temperature in Al/SiC, and 40% in Al/Al{dollar}sb2{dollar}O{dollar}sb3{dollar} composites. Hardness is improved remarkably by the incorporation of reinforcement. Optimum aging conditions for MMCs are determined. The peak aging time decreases with increasing the aging temperature and decreasing the volume fraction of reinforcement. Predictions for the elastic moduli and tensile strength are proposed from the transformed laminate analogy, and combinations of modified rule of mixtures and shear lag theory.; Wear resistance of composite is improved up to 1000%. The major wear mechanism of discontinuous MMCs is strongly dependent upon the sliding speed. Weight loss increases linearly with the sliding distance.; From fracture surface analyses at room and elevated temperatures, it is found that the failure mode is ductile at the microstructural level and it becomes more ductile as temperature increases. Based on the fracture surface observations and experimental data, the strength reduction at elevated temperatures is due to overaging and softening of the matrix alloy.; Failure mechanisms of the as-fabricated composite can be summarized as follows: (i) the initiation of microcracks at fiber ends and in the matrix, (ii) the formation of a major crack by the multiplication and coalescence of microcracks, and (iii) the inducement of the major crack to final fracture. Failure mechanisms of the heat treated composite include (i) the formation of the major crack at the precrack tip by linking microcracks, (ii) the initiation of many microcracks ahead of the major crack tip, and (iii) catastrophic failure due to the abrupt propagation of the major crack by the array of microcracks which are the weakest. (Abstract shortened with permission of author.)