High strain rate superplasticity in powder metallurgy aluminium alloy 6061+20 vol.-%SiCp composite with relatively large particle size

Abstract

The possibility of high strain rate superplasticity (HSRS) was examined over a wide range of temperatures in a powder metallurgy aluminium alloy 6061/SiCp composite with a relatively large SiC particle size of similar to 8 mu m. A maximum tensile elongation of 350% was obtained at 600 degrees C and 10(-2) s(-1). Tensile elongations over 200% were obtained in a narrow temperature range between 590 and 610 degrees C at high strain rates of 10-2 and 10(-1) s(-1). The current testing temperature range could be divided into two regions depending on the rate-controlling deformation mechanism. Region I is in the lower temperature range from 430 to 490 degrees C, where lattice diffusion controlled dislocation climb creep (n = 5) is the rate-controlling deformation process, and region II is in the higher temperature range from 520 to 610 degrees C, where lattice diffusion controlled grain boundary sliding controls the plastic flow. An abnormally large increase in activation energy was noted at temperatures above 590 degrees C, where large tensile elongations over 200% were obtained at high strain rates. This increase in activation energy and high tensile ductility may be explained in terms of presence of a liquid phase created by partial melting, but such evidence could not be provided by the current differential scanning calorimetry (DSC) test. This may be because the DSC is not sensitive enough to detect the small amount of liquid phase. MST/4499.