Superplasticity behavior and deformation mechanism of the in-situ Al3Zr/6063Al composites processed by friction stir processing

In this study, in-situ 5 wt % Al3Zr/60063Al composites were fabricated by direct melt reaction method and subjected to forging and friction stir processing (FSP) to achieve high-strain-rate superplasticity of the composites. Analysis determination technics of XRD, OM, SEM, TEM and high-temperature tensile tests were employed to study the microstructure, superplasticity property and deformation mechanism of the fabricated composites. The results show that the average grain size of the fabricated composites is less than 2 μm after the processing of forging and FSP. And the composites exhibited superplasticity at the temperature of 400 °C-550 °C with initial strain rate of 1.0 × 10−3 s−1 to 1.0 × 10−1 s−1. Especially, the elongation could reach the maximum value of 330%, with a strain rate sensitive exponent (m) of 0.45, initial strain rate of 1.0 × 10−2 s−1 and deformation temperature of 500 °C. Meanwhile, the strain rate sensitivity exponent was calculated to be 0.29-0.45 and the activation energy was 99.51-121.28 kJ/mol, which indicates that the key deformation mechanism of the composites was grain boundary sliding (GBS) accommodated by dislocation slip. Furthermore, the structure analysis of the composites shows that the FSP composites exhibits higher dislocation density (1.42 × 1015 m−2) than the as-cast composites (6.6 × 1014 m−2), which is benefit to the dislocation slip and grain coarsening, i.e. a useful softening mechanism of the composites to avoid quick work hardening during the high-strain-rate deformation.