Application of Hot Workability Studies to Extrusion Processing: Part II. Microstructural Development and Extrusion of Al, Al–Mg, and Al–Mg–Mn Alloys

Abstract

In uniform hot working tests, the flow curves strain harden to a steady state plateau that depends on temperature and strain rate. The underlying mechanism is dynamic recovery which rises with strain to balance the work hardening, resulting in subgrains that are larger and more perfect as T rises and E falls. Subgrains are observed in the extrudate following the pattern established in hot workability tests. Moreover, their formation in the upset billet and throughout the deformation zone has been examined as a means to delineate its thermal and mechanical development. Substructure in the extrudate substantially improves its mechanical properties. With increasing Mg solute, substructure recovery is reduced so that the strength and the tendency for recrystallization are increased. Moreover, in alloys above 5% Mg, most notably containing large Mn-rich constituent particles, dynamic recrystallization nuclei form in the most intensely strained regions of the deformation zone and also speed up static recrystallization in the extrudate.Resume-Lors d'essai de formage a chaud uniforme, les courbes d'ecoulement se durcissent par ecrouissage jusqu'a un plateau constant qui depend de la temperature et du taux de deformation. Le mecanisme sousjacent est la restauration dynamique qui augmente avec la deformation pour balancer Ie durcissement par ecrouissage, resultant en sous-grains qui sont plus gros et plus parfaits a mesure que la T s'eleve et que f s'abaisse. On observe des sous-grains dans la forme d'extrusion, suivant Ie modele etabli lors d'essais de formage a chaud. De plus, on a examine leur formation dans la billette refoulee et dans toute la zone de deformation, comme un moyen de delimiter leur developpement thermique et mecanique. La sous-structure dans la forme d'extrusion ameliore substantiellement ses proprietes mecaniques. Avec une augmentaion du solute de Mg, la restauration de la sous-structure est reduite de telle sorte que la resistance et la tendance ala recristallisation sont augmentees. De plus, dans les alliages de plus de 5% Mg, contenant visiblement de grosses particules constituantes riches en Mn, des noyaux de recristallisation dynamique se forment dans les regions les plus intensement deformees de la zone de deformation et aussi augmentent la vitesse de recrisallisation statique de la forme d'extrusion.

Microstructure and mechanical property studies of AA6056 friction stir welded plate

“…4(b)) is wider due to the tool rotation causing the material ahead of it to displace to the right-hand side. This sheared, rotated material has a continuous decrease from the pin surface in strain, strain rate and temperature, like the gradient from die surface to center of an extruded rod [19][20][21][22]. Furthermore, the TMAZ band closest to the nugget appears as a mixture of fine crystallites, approaching the cell dimension in the elongated grains, as already noted for the advancing side TMAZ-nugget interface.…”

“…Some SRV occurs after all straining has stopped, but it is much less effective than DRV [45]. In an extrusion, the strain, strain rate and temperature rise with approach to the surface, so that subgrains are smaller, but there is no period of declining strain rate [19][20][21][22]. A more extensive description of the model is presented elsewhere [46].…”

“…The time at high temperature after straining is too short for discontinuous dSRX to take place even at interfaces between the equiaxed and elongated regions with greater substructure density. In an extrusion, dSRX sometimes occurs in the highest strain rate region closest to surface due to slow cooling, but is clearly distinguishable from the substructure [19,20].…”

The High-Speed 6xxx Aluminum Alloys in Shape Extrusion Industry

“…The size of stable subgrains that result from dynamic recovery in aluminum alloys depends upon hot working conditions. McQeen et al [30] expressed this by equation:…”