Relationship of particle stimulated nucleation, recrystallization and mechanical properties responding to Fe and Si contents in hot-extruded 7055 aluminum alloys

Abstract

The variations of coarse intermetallic particles in hot-extruded 7055 aluminum alloys with 0.041 wt% Fe and 0.024 wt% Si increasing to 0.272 wt% Fe and 0.134 wt% Si were investigated. The particle stimulated nucleation (PSN) behaviors for different kind of coarse particles were detailly analyzed by EBSD. Moreover, the effect of PSN responding to Fe and Si contents on recrystallization and tensile properties of 7055 alloys was evaluated. With increasing Fe and Si contents, the size and number density of coarse η/S particles are reduced, while the number densities of coarse Al7Cu2Fe and Mg2Si particles are both increased and the coarse Al7Cu2Fe particles transform from rod-like to irregular. More PSN recrystallized grains with predominant orientations deviated from the extruded fiber textures are stimulated by the irregular Al7Cu2Fe and Mg2Si particles, because a higher degree of local non-uniform deformation is produced. The rod-like Al7Cu2Fe particles cause the greatest degree of local non-uniform deformation owing to the largest aspect ratio, but the shape also restricts the area of particle deformation zone (PDZ) resulting in fewer PSN recrystallized grains. The irregular η/S particles give rise to the lowest degree of local non-uniform deformation and fewest PSN recrystallized grains with the major orientations close to the extruded fiber textures. Consequently, despite the number and size of coarse η/S particles are reduced, the proportion of high angle grain boundaries (HAGBs) is increased and the extruded fiber textures are weakened with Fe and Si contents increasing, because of the increased Al7Cu2Fe and Mg2Si particles. The strength is slightly declined by the weakened <111>//ED (extrusion direction) fiber texture, while the elongation is reduced for a larger number of coarse particles and more HAGBs with higher Fe and Si contents.