The Effect of Grain Size Gradient on Plastic Deformation of Gradient Aluminum

Abstract

Grain size gradient materials exhibit superior strength and ductility due to their multiscale microstructures. A dislocation-based multiscale model was applied to study the effect of grain size gradient on the flow stress and deformation of gradient Aluminum. It is found that the grain orientation has a slight effect on the macroscopic behavior of gradient Aluminum, but without a strong texture fiber, such effect is neglectable. The strength depends not only on the average grain size but also on the grain size gradient. By varying the grain size gradient in the region connecting finest 200 nm grains and coarse grains in tens of microns, we found that the plastic flow stress is inverse proportional to the grain size gradient. A smooth transit could lead to a redistribution of the stress concentration and strain localization. The results on the deformation of different grain size gradients Aluminum shed light on processing gradient materials with an improved combination of strength–ductility.

Appendices

Appendix 1

The fitting of parameters q1–q7 with the evolution equations to [001] orientation tensile of single-crystal Aluminum is shown in Figure 7 (the red line). Then the set of parameters was adjusted based on the standard deviation of stress from simulations and experiments (the blue and purple line) from [111] loading directions in Figure 7.

Fig. 7

Stress–strain curves of tensile tests of single-crystal Aluminum (Color figure online)

Appendix 2

The equivalent plastic strain and mobile dislocation contour of homogeneous case with equivalent grain size are plotted on interpolation with a natural function with samples straining to 15 pct (Figure 8 ).

Fig. 8

Contour plots of (a) equivalent plastic strain and (b) mobile dislocation density for homogeneous case at strain 15 pct

Tensile simulations of two homogeneous microstructure cases with identical regions but different numbers of grains (different average grain sizes, 3.5 and 50 μm, respectively). As shown in Figure 9 , the case with a smaller average grain size would have much higher strength but less strain hardening than the larger average grain size case. The average dislocation density in larger grains is much higher than that in smaller grains.

Fig. 9

(a) Stress–strain curves, and (b) total mobile dislocation density for homogeneous microstructure with average grain size 3.5 and 50 μm