The effect of second-phase particles on grain refinement during equal-channel angular pressing in an Al–Cu–Mg–Ag alloy

Abstract

In this work, the effect of second-phase particle distributions on grain refinement during equal-channel angular pressing (ECAP) was studied at 250°C by comparing the microstructural evolution in an Al-Cu-Mg-Ag alloy processed in three different states. The first state (QA) was obtained by water quenching, and the second state was obtained by overaging at 250°C. Both these states contain fine dispersions of X-phase shearable plates with coherent and/or semi-coherent interfaces. The QA plate thickness prior to ECAP was higher by a factor of four than in the OA. The third alloy (HA) contained relatively coarse non-deformable particles of thermodynamically equilibrium phases with incoherent interfaces. It was shown that distribution of the secondary phase particles strongly affects the continuous dynamic recrystallization through the initial formation of geometrically necessary boundaries (GNBs), pinning dislocations and deformationinduced boundaries. The formation of a fully recrystallized structure occurs at the highest rate in the HA material with rounded grains because of 3D networks of low-angle boundaries (LABs) evolve at e * 1 due to the concurrent formation of GNBs belonging to two families. In the QA and OA materials, the shearing of the X-phase plates with the coherent interfaces leads to the strong localization of dislocation slip and the dominant formation of one family of GNBs. Nonshearable nanoscale dispersoids hinder the formation of 3D arrays for GNBs. As a result, only a partially recrystallized structure evolves, even at strains of up to e * 12.

Microstructural and texture changes during equal channel angular pressing of an Al–Mg–Sc alloy

“…Hence, deformation mechanisms, other than uniform on the mesoscopic level dislocation slip, should appear to be more important at large strains, promoting substantial changes in the texture and microstructural evolution. In turn, the development of well-defined banded structures composed of MSBs caused by the strong lattice rotations in some crystals (or in their groups), simultaneously triggers the dynamic nucleation of new grains and, thus, promotes grain refinement [8,12,14,19,26,30]. Some features of rigid lattice rotations and grain refinement during ECAP of the present alloy will be discussed below with reference to its crystallographic texture.…”

“…Several studies regarding the texture evolution in Al and its alloys [e.g., 3,16,17,[19][20][21]25,30] have demonstrated a similarity between the textures developed by ECAP and those imposed by a simple shear large-strain deformation. At the same time it is worth to expect that some additional lattice rotations can take place when the specimen is processed by repetitive ECAP [15].…”

“…[2][3][4][5][7][8][9][10][11][12][13][14]19,26,28,30]. It has been found that the major mechanism of strain-induced formation of new grains in aluminum alloys was the continuous dynamic recrystallization (cDRX) [8,12,14,26,28,30,31].…”

“…[2][3][4][5][7][8][9][10][11][12][13][14]19,26,28,30]. It has been found that the major mechanism of strain-induced formation of new grains in aluminum alloys was the continuous dynamic recrystallization (cDRX) [8,12,14,26,28,30,31]. The structure evolution was characterized by the formation of deformation bands such as microshear bands (MSBs) at moderate strains, followed by their transformation to ultrafine grains with high-angle boundaries (HABs) at large strains [8,9,[12][13][14]23,28,30].…”

Melt treatment of Al–Si foundry alloys with B and Sr additions

“…While wrought alloys can be grain refined in the solid state via thermomechanical processing [1][2][3][4][5][6], foundry alloys must be grain refined during casting. Grain refinement offers uniform structural features, superior mechanical properties, reduced shrinkage as well as better surface quality and is thus a key melt treatment in aluminium foundries [7].…”