Adiabatic shear failure of aluminum matrix composites and microstructural characteristics of transformed bands

Adiabatic shear failure of aluminum matrix composites and microstructural characteristics of shear bands were investigated by means of SEM, TEM and HREM. Results revealed that the shear bands characterized as melting phase transformation of aluminum alloy (Al(s)→Al(l)) were caused by local adiabatic temperature increase. Numerous melted aluminum cells with a diameter of 1-3 µm are observed on the surfaces of transformed bands. A large number of dislocations and fine grains (≤100 nm) were found around the edge of the transformed band. In the center of the bands, amorphous, nanocrystalline grains and ultrafine-grains were observed. It was analyzed that temperature and temperature heterogeneities were important for the formation of amorphous in transformed bands. Aluminum matrix composites reinforced with high reinforcement volume fraction acted as classical thermo-plastic shear instability; both shearing and splitting failure were induced by shearing localization.