PNNL

Abstract

Aim of this study is to obtain a high volume fraction of uniformly distributed of reinforcement particles in aluminum metal matrix composites (AMC), which is not possible with conventional melt-based methods. Friction consolidation method is utilized to reinforce Aluminum 7075 alloy with high volume fractions (12 and 24 vol%) of titanium diboride (TiB2) by high pressure and severe plastic deformation at elevated temperatures. The consolidated AMCs have a uniform dispersion of submicron- and micron-sized TiB2 particles in the AA7075 matrix. High shear deformation results in a two-fold refinement of TiB2 particles and a three-fold refinement of the aluminum grain structure. The addition of TiB2 significantly increases hardness by up to 50%, Young’s modulus by up to 65%, and ultimate strength by up to 30%, while reducing ductility by 80%. Pin-on-disc wear tests revealed a 7-fold improvement in wear rate for 7075/24vol% TiB2 compared to the unreinforced sample. A microstructure-based finite element (FE) modeling predicted the mechanical and fracture behaviors of the AMCs. It indicated that high triaxiality, in conjunction with equivalent plastic strain in a narrow area between the TiB2 particles led to initial fractures which limited the ductility of the composites.