The relationship of dislocation and vacancy cluster with yield strength in magnetic annealed UFG 1050 aluminum alloy

The evolutions of tensile properties and microstructures of ultrafine grained (UFG) 1050 aluminum alloy after annealing at 90-210 degrees C for 4 h without and with 12 T high magnetic field were investigated by tensile test, electron back scattering diffraction pattern (EBSD), transmission electron microscopy (TEM) and positron annihilation lifetime spectroscopy (PALS). When annealing temperature increases from 90 degrees C to 150 degrees C, the yield strength (YS) of UFG 1050 aluminum alloy increases, it is because that the increase in the density of vacancy clusters due to the activated monovacancies and the high angle boundaries (HABs) having more stable structures, both of them can act as effective barriers to dislocation motion during tensile deformation. When annealing at 210 degrees C, the YS of UFG 1050 aluminum alloy deceases, it is because that the decrease in the vacancy clusters density due to the thermally activated the vacancy clusters annihilating at sinks and the dislocation density decreases. The YS of magnetic annealed samples are lower at 90 degrees C and 150 degrees C due to the lower density of dislocations and vacancy clusters. The difference of YS between samples annealed without and with magnetic field disappears at 210 degrees C due to the sharply reduced strain hardening stage.