Study on the three-dimensional tensile creep anisotropy of a hot-rolled Mg-0.9Mn-1.5Ce alloy sheet

Abstract

In this work, the three-dimensional tensile creep anisotropy of a hot-rolled Mg-0.9Mn-1.5Ce (wt%) alloy sheet was investigated. Creep tests were carried out at 453 K, 473 K and 493 K under various applied stresses. The loading directions were parallel to the transverse direction (TD), rolling direction (RD), and normal direction (ND). Experimental results showed that creep behavior had a strong dependence on the loading direction under the given ranges of stress and temperature, in which the creep resistance was ranked in the order of TD ≈ RD> ND. Thermodynamic calculations and microstructure characterization illustrated that the creep mechanism displayed an intense dependence on stress and temperature in the TD and RD samples, which exhibited similar creep behaviors. Specifically, the viscous gliding of dislocations dominated the creep at 453 K. Pyramidal< c + a> slip started to activate and gradually controlled the creep because of the thermal activation at 473 K. As the temperature increased to 493 K, dislocation climb and pyramidal< c + a> slip together controlled the creep. Conversely, the creep mechanism barely changed in the ND sample, which included {101̅2} twinning and cross-slip. The dense twins developed in the ND sample directly caused early creep fracture, and< a> dislocation cross-slipping between the basal plane and prismatic plane supplied a large creep strain and accelerated creep rate. Unexpectedly, the heavy interactions between pyramidal dislocations and dynamic precipitates offered an extra strengthening factor for creep resistance in the TD and RD samples. Consequently, the poorest creep resistance was obtained in the ND sample. In addition, the breakaway of dislocations from the solute atmosphere or precipitates by climbing was the main reason for the power-law breakdown at 493 K in the TD and RD samples.