Effect of warm rolling and annealing on the mechanical properties of aluminum composite reinforced with boron nitride nanotubes

The effect of rolling and annealing on boron nitride nanotube (BNNTs) reinforced aluminum- composites is investigated in this study. Composites were fabricated via conventional sintering method with 0, 2 & 5 wt% BNNT addition in aluminum matrix. Addition of 2 wt% BNNT improved hardness and elastic modulus by 23% and 18%, respectively. Rolling the same composite at 200 °C with 60% reduction in single pass improved modulus and hardness of the composite by 60% and 31%, respectively, over Al. Addition of 5 wt% BNNT led to reduced properties due to agglomeration, which on rolling developed cracks. Annealing the rolled Al-BNNT composite further led to an improvement in strength and ductility. Annealed Al-2BNNT showed highest improvement in strength of 41% and 110% over rolled and sintered condition, respectively. In addition, the same composition has recorded 157% improvement in toughness in annealed condition, as compared to rolled condition. Uniformly distributed BNNTs restricted grain growth and grain boundary migration due to pinning, leading to presence of additional grain boundaries inside the old grains thus improving the strength further. Uniform distribution of BNNT is the prime reason behind the improved properties of Al-BNNT composites.