Hardness and tensile strength study on Al356–B 4 C composites

Abstract

Additions of high modulus particles to aluminium alloys offer the potential to develop a lightweight composite with high strength and hardness. Al356 matrix composites reinforced with B₄C particles were prepared using stir casting method. Hardness and tensile strength of unreinforced alloy and composites with different volume percentages of boron carbide particles were measured and compared. Microstructural characterisation revealed an almost uniform distribution of the B₄C particles in the matrix. It also showed that the grain size of aluminium composite is smaller than that of monolithic aluminium. X-ray diffraction studies also confirmed the existence of boron carbide and some other reaction products, such as AlB₂ and Al₃BC, in composite samples. It is observed that the mechanical properties enhance with increasing particle fraction. The great enhancement in values of ultimate tensile stress and hardness observed in this experiment is due to small particle size and good distribution of the B₄C particles, which was confirmed by SEM images. According to the results of this experiment, quite significant improvement in strength is noted when 10 vol.-B₄C particles is added; a further increase in B₄C content leads to a reduction in strength values. This might be the result of greater agglomeration of particles and higher degree of microporosity present in the composite at higher B₄C content.