A high-strength aluminium-based alloy with advanced superplasticity

Abstract

The structure, mechanical properties and superplastic behaviour of a high-strength Al–(3.5–4.5)Zn–(3.5–4.5)Mg–(0.7–0.9)Cu–(1.0–3.0)Ni–(0.25–0.30)Zr (wt.%) alloy are investigated. A 570MPa YS and a 610MPa UTS are achieved after T6 heat treatment. The alloy exhibits superplasticity in the temperature ranged from 380 to 480°C at constant strain rates from 2×10−3 to 1×10−1s−1 with a strain rate sensitivity index greater than 0.5 and an elongation of 400–800% due to the stable ultrafine structure with 1.8μm grain size. An EBSD study of the deformation behaviour demonstrated substantial grain refinement resulting from dynamic recrystallisation. High strain rate superplasticity is available due to zirconium addition that provides Zener pinning of grain boundaries, and nickel addition that forms Al3Ni eutectic particles which improved superplasticity due to grain refinement by particle stimulated nucleation.