In this paper, studies were conducted to investigate the deformation behavior and microstructure change in a hot-rolled AZ31B magnesium alloy during a tensile-tensile cyclic loading. The relationship between ratcheting effect and microstructure change was discussed. The ratcheting effect in the material during current tensile-tensile fatigue loading exceeds the material’s fatigue limit and the development of ratcheting strain in the material experienced three stages: initial sharp increase stage (Stage I); steady stage (Stage II); and final abrupt increase stage (Stage III). Microstructure changes in Stage I and Stage II are mainly caused by activation of basal slip system. The Extra Geometrically Necessary Dislocations (GNDs) were also calculated to discuss the relationship between the dislocation caused by the basal slip system and the ratcheting strain during the cyclic loading. In Stage III, both the basal slip and the {11−20} twins are found active during the crack propagation. The fatigue crack initiation in the AZ31B magnesium alloy is found due to the basal slip and the {11−20} tensile twins.

In this paper, infrared thermography was employed to study the fatigue process of AZ31B magnesium alloy. In order to eliminate the interference caused by the temperature rise of the fixture, a data processing method was proposed, which is based on a special model to describe the temperature change of the specimen. Based on the temperature data after processing, the temperature evolution indicates that AZ31B magnesium alloy has undergone cyclic hardening during fatigue. Three different temperature indicators were selected to evaluate the fatigue limit based on the evolution curve after processing. In addition, the experimental results showed that the temperature data processed by the proposed method can be used to estimate the fatigue limit of AZ31B magnesium alloy. Experiments were performed for both extrusion and transverse directions in consideration of the anisotropy of the AZ31B.

In this paper, the fatigue limit of AZ31B magnesium alloy is evaluated according to the surface temperature of the specimen during the test. Considering the influence of external heating, a special data-processing method is used to filter the raw temperature data obtained by the infrared camera. A thermal indicator based on the analysis of superficial temperature distribution is described and proposed. In contrast, most existing thermal indicators are calculated based on temperature evolution. Three existing algorithms were used to evaluate the fatigue limit of AZ31B magnesium alloy based on the newly proposed thermal indicator. In addition, the results of the test were used to compare with the results of traditional methods. It has been proved that the fatigue limit of AZ31B magnesium alloy can be assessed by using the new thermal indicator based on temperature distribution.

AZ31B magnesium alloy is the experimental material in this study. Considering its anisotropy, fatigue assessment based on self-heating is carried out for both the extrusion direction and the transverse direction. The self-heating behavior in the two orientations is compared. Similar to steels, an obvious inflection point that corresponds to the fatigue limit can be found in the self-heating vs. load curve for AZ31B. A new fatigue limit assessment method is proposed based on a statistical analysis of self-heating data. This method can provide a satisfactory assessment of the fatigue limit for AZ31B in the both orientations.