Low-temperature plastic deformation of AZ31 magnesium alloy with different microstructures

Abstract

The plastic deformation of AZ31 magnesium alloy under tension at temperatures of 4.2–295K is studied as a function of its microstructure following squeeze casting (SC) and after severe plastic deformation (SPD) by hot rolling and equal-channel angular pressing. SPD reduces the average grain size and creates a texture that favors basal-plane dislocation glide. It is found that plastic deformation becomes unstable (serrated) at temperatures of 4.2–25K and more stress jerks occur in the SPD polycrystal than in the SC alloy. The temperature dependence of the yield stress of the alloy is typical of thermally activated unpinning of dislocations from short-range barriers. The ratio of the yield stresses for the SPD and SC alloys at a given temperature is explained by hardening owing to a reduction in grain size and softening owing to a favorable texture. As the grain size is reduced, the rate of strain hardening of the alloy falls off, but its ductility (strain to fracture) increases because of the texture. The strain rate sensitivity of the alloy for T⩽100K is independent of microstructure and is determined by intersections with forest dislocations. As the temperature is raised over 150–295K the strain rate sensitivity becomes greater owing to activation of dynamic recovery and an enhanced contribution from diffusion processes during plastic deformation of micrograined materials.

Microstructure and properties evolution of Mg–2Y–0.6Nd–0.6Zr alloy rolled at room and liquid nitrogen temperature

“…The CRSS values of prismatic and pyramidal slips are as high as 40 MPa or more 18 , but it decreases significantly with increasing temperature. In Mg alloys {10 1}, the CRSS required for compression twins is 76–153 MPa 19 , which is much greater than the CRSS (2–3 MPa) required for {10 2} tensile twins 20 , 21 . In conclusion, the above reasons can also explain that 86° <11 0> tensile twins are more likely to appear during ultra-low temperature rolling.…”

Effect of friction stir processing parameters on producing AA6061/ tungsten carbide nanocomposite

“…78 Small grains have a higher resistance to crack propagation due to strain distribution between grain boundaries. 79,80 The fracture mode for Exp. 2 shows a high ductility and lower UTS indicated by lower and deeper dimples, whereas larger and shallow dimples for Exp.…”

Study on the effect of the welding environment on the dynamic recrystallization phenomenon and residual stresses during the friction stir welding process of aluminum alloy

“…Bagheri et al 56 noted that grain boundaries reduce the growth of cracks within the microstructure and postpone the fracture, which results in an increase in ductility. Estrin et al 57 found that intergranular fracture transforms to transgranular fracture as grain size decreases and ductility increases as grain size decreases. Das et al 58 also indicated that as grain size reduces, the density of geometrically necessary dislocations, which accommodated the strain among the grains increases, and ductility increases.…”