Microstructure, Mechanical Properties and Strain Hardening Behavior of Alternative α/β Mg-Li Composite Sheets Prepared by Accumulative Roll Bonding

To improve comprehensive mechanical properties of Mg-Li alloy, alternative alpha/beta Mg-Li composite sheets with a bimodal-grained structure were prepared by accumulative roll bonding (ARB). The microstructure, texture, mechanical properties and strain hardening behavior of the alternative alpha/beta Mg-Li composite sheets were studied. The bimodal grain structure, with ultrafine grains (about 0.79 mu m) in the alpha alloy and coarse grains (about 53.28 mu m) in the beta alloy, can be observed in the composite sheet. The dominant texture of alpha-Mg and beta-Li alloys is {0002} basal texture and {110} texture, respectively. In the alpha alloy, the basal texture decreases gradually with the increase of ARB pass, and the non-basal texture is formed in the sheet processed by 5-pass ARB. The dislocation density of the composite sheet gradually increases and approaches saturation after 3-pass ARB process due to the balance between dislocation accumulation in the ARB process and dislocation annihilation in dynamic recovery. The sheet processed by 3-pass ARB has the preferable strength and plasticity, with yield strength, ultimate tensile strength, elongation of 204 MPa, 216 MPa, 22.73%, respectively. Compared with the as-annealed alloys before ARB, the strain hardening rate of the ARB composite sheets increases gradually at low stress (stage II). Mg-Li sheets produced by ARB process remain a high plasticity because of the longer softening stage (stage III), which is mainly contributed to the synergistic effect of the bimodal grain structure and the activation of non-basal texture.

Automated summary

Alternative alpha/beta Mg-Li composite sheets with a bimodal-grained structure were prepared by accumulative roll bonding (ARB). The sheets exhibit a balance between dislocation accumulation and annihilation, leading to preferable strength and plasticity after 3-pass ARB process. The strain hardening rate gradually increases at low stress in the ARB composite sheets, which remain highly ductile due to the synergistic effect of bimodal grain structure and activation of non-basal texture.