The effect of friction stir-back extrusion speed on Al-Cu-Mg-Li alloy microstructure and corrosion behaviour

Abstract

ABSTRACT In this study, the effect of extrusion speed on the microstructure and corrosion behaviour of a friction stir-back extruded Al-Cu-Mg alloy containing 0.5 wt.% Li was investigated. Results show that friction stir-back extrusion on an as-cast aluminum alloy with a dendritic microstructure forming finely equiaxed recrystallized grains. With decreasing extrusion speed from 80 to 40 mm/min, the average grain size increases from 6.0 ± 1.2–9.8 ± 3.2 µm. After friction stir-back extrusion, the morphology of the Cu-Mg-rich precipitates has completely changed, and the fine precipitates (0.25-0.42 µm) with a uniform distribution have formed in the microstructure of the extruded wires. With the reduction of the extrusion speed from 80 to 40 mm/min, the accumulated strain in the extruded wires increases from 0.006-0.011. Compared to as-cast alloy, friction stir-back extrusion results in at least 23, 37, and 22% increases in yield strength, tensile strength, and elongation. The minimum corrosion current (1.32 × 10−4 A.cm−2) and corrosion rate (0.003 mm/year) were achieved in the wire extruded at a rotational speed of 800 rpm and an extrusion speed of 60 mm/min.