Aluminium Matrix Composites Reinforced with Si₃N₄, AlN and ZrB₂, Produced by Conventional Powder Metallurgy and Mechanical Alloying

Abstract

The homogeneous distribution of the reinforcement phase is a prime requisite for a composite material to present its superior performance. Powder metallurgy can produce composite materials in the whole range of matrix reinforcement composition, without the segregation typical of the casting process, and mechanical alloying serves to optimise the particle mixing stage, enhancing the reinforcement distribution. This work investigates the use of mechanical alloying plus hot extrusion to obtain Al6061 matrix composites reinforced with Si₃N₄, AlN and ZrB₂, and compares the result with the same composite materials obtained by more conventional powder metallurgy techniques. The incorporation of the reinforcement does not suffice to produce a significant improvement of the mechanical properties of the conventional powder metallurgy composites. Mechanical alloying breaks the reinforcement particle clusters, eliminates most of the defects present in these particles, decreases their size and enhances their distribution, which together with the metallurgical phenomena that change the metallic matrix, such as work hardening and oxide and carbide dispersion, produces an increase of about 150% in the hardness of the powder, when compared with the hardness of the as-received, non-reinforced aluminium powder alloy; and of 100% in the hardness and ultimate tensile strength of the consolidated materials, when compared with material of same composition processed by conventional powder metallurgy.