Mechanical properties and dislocation substructure of 6061-T6 aluminum alloy impacted at cryogenic temperatures

Abstract

The mechanical properties and dislocation substructure of 6061-T6 aluminum alloy deformed at temperatures of 0°C, -100°C and -196°C and strain rates of 1000 s-1, 3000 s-1 and 5000 s-1 are investigated using a compressive split-Hopkinson pressure bar. It is found that the flow stress and strain rate sensitivity increase with increasing strain rate, but decrease with increasing temperature. In addition, the work hardening rate decreases with increasing strain rate and temperature. The flow stress corresponding to a true strain of 0.6 is modelled using a power law expression with an activation energy of 1.7 kJ/mol and an average strain rate sensitivity of 0.154. The dislocation density increases with increasing strain rate and decreasing temperature, and leads to a greater flow stress. A greater multiplication and tangling of the dislocations occurs at higher strain rates and lower temperatures. The flow stress and square root of the dislocation density are linearly related via the Bailey- Hirsch type relation σ = σ0 + α1 Gb p, where α1 has a value of 0.46 for the current 6061-T6 aluminum alloy.