Simulation of strain induced abnormal grain growth in aluminum alloy by coupling crystal plasticity and phase field methods

A mesoscale modeling methodology is proposed to predict the strain induced abnormal grain growth in the annealing process of deformed aluminum alloys. Firstly, crystal plasticity finite element(CPFE) analysis is performed to calculate dislocation density and stored deformation energy distribution during the plastic deformation. A modified phase field(PF) model is then established by extending the continuum field method to consider both stored energy and local interface curvature as driving forces of grain boundary migration. An interpolation mapping approach is adopted to transfer the stored energy distribution from CPFE to PF efficiently. This modified PF model is implemented to a hypothetical bicrystal firstly for verification and then the coupled CPFE-PF framework is further applied to simulating the 2D synthetic polycrystalline microstructure evolution in annealing process of deformed AA3102 aluminum alloy.Results show that the nuclei with low stored energy embedded within deformed matrix tend to grow up, and abnormal large grains occur when the deformation is close to the critical plastic strain, attributing to the limited number of recrystallized nuclei and inhomogeneity of the stored energy.

Formation mechanism and evolution of surface coarse grains on a ZK60 Mg profile extruded by a porthole die

Porthole die extrusion of Mg alloys was studied by means of experimental and numerical studies. Results indicated that an inhomogeneous microstructure formed on the cross-section of the extruded profile. On the profile surface, abnormal coarse grains with an orientation of <11-20> in parallel to ED(extrusion direction) appeared. In the profile center, the welding zone was composed of fine grains with an average size of 4.19 um and an orientation of <10-10> in parallel to ED, while the matrix zone exhibited a bimodal grain structure. Disk-like, near-spherical and rod-like precipitates were observed, and the number density of those features was lower on the profile surface than that in the profile center. Then, the formation and evolution of coarse grains on the profile surface were investigated, which were found to depend on the competition between static recrystallization and grain growth. The stored deformation energy was the factor dominating the surface structure through effective regulation over nucleation of the precipitates and recrystallization. A profile with a low stored deformation energy suppressed formation of precipitates and consequently facilitated grain growth rather than recrystallization, resulting in the formation of abnormal coarse grains. Finally, the surface coarse grains contributed detrimentally to hardness, tensile properties, and wear performance of the bulk structure.

Enhanced dye degradation capability and reusability of Fe-based amorphous ribbons by surface activation

The dye degradation capability and reusability of FeSiBNbCu amorphous ribbons are largely enhanced due to the surface activation by ball milling.The time required for degrading 50%of acid orange 7 solution by the activated FeSiBNbCu amorphous ribbons is only 1/6 of that by the as-quenched ribbons,while the reusable times of the activated ribbons is 6 times larger than that of the as-quenched ribbons.The superior degradation capability and better reusability of the activated FeSiBNbCu amorphous ribbons come from not only the uneven topography of the ribbon surface induced by ball milling,but also the stored deformation energy,including the structural rejuvenation and the enlarged residual stress.The structural rejuvenation in the activated FeSiBNbCu amorphous ribbons is verified by heat relaxation analysis,and the increased residual stress is confirmed by the magnetic domain measurements on the ribbon surfaces.Besides,the environmental adaptability of the activated FeSiBNbCu amorphous ribbons is also investigated.The possible pathways for degradation of acid orange 7 using the activated ribbons,including azo bond cleavage and hydroxylation of benzene ring,are proposed.This work provides a new method to effectively improve the degradation performance of amorphous ribbons.