TEM and DSC Investigation of the Recovery of a Recycled Aluminum Processed by Equal Channel Angular Extrusion

Abstract

TEM investigation was performed on a recycled aluminum processed by Equal Channel Angular Extrusion. The aluminum contains many inclusions which were identified to be rich in iron and silicon.This has a substantial effect in dragging recovery. ECAE was performed via routes B and C using a die formed by two channels characterized by the well defined angles =90° and  = 90°. The evolution of the microstructure seems to be similar whether using route B or C. a high dislocation density was introduced since the first passage together with a high density of Frank dislocation loops. The latter are due to a by-passing of inclusions by cross-slip mechanism. Weak beam experiments enable us to investigate the early stages of recovery consisting in the formation of dislocation walls and few dislocation cells. A partial arrangement of dislocations was observed since the first passage through the die. The formation of dislocation cells began already before annealing and progresses at more elevated temperatures. The substantive recovery seems to push recrystallization process to high temperatures. By contrast, DSC investigations show a significant difference: The amount of energy deduced from the area of the peak relative to recrystallization is higher when using route C.

Influence of temperature cycles on strength and microstructure of spray-deposited Si–Al CE9F alloy

“…The enthalpy corresponding to the first recovery peak between 125 and 250°C is about 0.03 J g −1 (assuming a nominal composition of 40 wt.% Al in the DSC sample). This value lies in the range reported in (Rebhi et al, 2011), between 0.01 and 0.06 J g −1 .…”

“…The high temperature peak is attributed to recrystallization. Recovery peaks were also reported for a recycled aluminum alloy subjected to severe plastic deformation by equal channel angular pressing between 90 and 200°C (attributed to recovery), between 200 and 300°C (attributed to recrystallization) and between 300 and 350°C (attributed to grain growth) (Rebhi et al, 2011;Makhlouf et al, 2012).…”

“…These recovery phenomena are probably related to the first DSC peak spread between 125 and 250°C while scanning at 20 K min −1 (Fig. 8), and attributed to recovery in (Rebhi et al, 2011;Makhlouf et al, 2012).…”