Hardness and tensile strength study on Al356–B4C 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.