Effect of Partially Recrystallized Structure Produced by Intense Plastic Deformation on Fatigue Behavior of an Al6%Mg0.3%Sc Alloy

Abstract

t was shown that ECAP of an Al6%Mg0.3%Sc through route C at a temperature of 325°C (0.6Tm) to a total strain of 8 leads to the formation of partially recrystallized structure; the average size and the volume fraction of new ultrafine grains (UFG) were 1.2μm and 0.7, respectively. Areas of UFG structure alternate with coarse remnant parts of deformed original grains. Effect of this bimodal structure on room-temperature mechanical properties including fatigue behavior is examined. The ECAP processing led to increase in the yield strength and endurance limit accompanied with an insignificant loss of plasticity. Analysis of the surface features indicated that the fracture upon cyclic loading occurred by the transgranular mode in the regions of the unrecrystallized grains; this followed from the presence of striations in the large flat regions of the samples. In contrast, the fracture within regions of UFG grains occurred by the intergranular mode; distinct boundaries were clearly observed between the adjacent facets. It is concluded that the ultrafine grains presenting in the bimodal structure increase the strength characteristics of the alloy whereas the large remnant grains provide its relatively high plasticity. Therefore, the bimodal structure produced by the ECAP may ensure a certain balance between the rate of nucleation and propagation of a fatigue crack. The influence of this microstructure on the fatigue behavior of the material is discussed in detail.