The purpose of this research is to investigate the statistical behavior of fatigue crack propagation(FCP) in magnesium alloy AZ31. FCP tests have been performed on compact specimens of AZ31 at load ratio conditions and maximum fatigue load conditions to obtain statistical data of FCP. It was found that the variability of fatigue crack propagation rate was significantly large at initial stage of FCP and gradually became smaller as the fatigue crack propagated. The finding of the study showed that increasing the load ratio could increase the variability of fatigue crack propagation rate at initial FCP stage. The samller the load ratio, the higher the fatigue crack propagation rate at initial stage. It was also found that the load ratio is a factor affecting the fatigue crack propagation rate in magnesium alloy.

AZ31 magnesium alloy was used to manufacture a thin plate using a melt drag method. The effects of roll speed, molten metal temperature, and molten metal height, which are the basic factors of the melt drag method, on the surface shape, the thickness of the thin plate, Vickers hardness, and microstructure of the thin plate were investigated. It was possible to manufacture AZ31 magnesium alloy thin plate at the roll speed range of 1 to 90 m/min. The thickness of the thin plate, manufactured while changing only the roll speed, was about 1.8 to 8.8 mm. The shape of the solidified roll surface was affected by two conditions, the roll speed and the molten metal height, and the Vickers hardness of the manufactured magnesium alloy thin plate value ranged from Hv38~Hv60. The microstructure of the thin plate produced by this process was an equiaxed crystal and showed a uniform grain size distribution. The grain size was greatly affected by the contact state between the molten metal and the solidification roll, and the amount of reactive solids and liquids scraped at the same time as the thin plate. The average grain size of the thin plate fabricated in the range of these experimental conditions changed to about 50-300 μm.

The objectives of this paper are to evaluate the factors affecting the fatigue crack propagation(FCP) behavior in AZ31 magnesium alloy. FCP experiments have been performed on the specimens of AZ31 magnesium alloy under various conditions such as a loading frequency, a specimen thickness, a maximum fatigue load, and a load ratio and the obtained results were analyzed to find the influence factors on the FCP behavior in magnesium alloy. It is necessary to consider the influence factors for the design and the maintenance of lightweight structures. The correlation between the crack growth rate exponent and the crack growth rate coefficient, which are FCP behavior parameters, was also analyzed and the regression model was presented.

Recently magnesium alloy sheet has been used as a lightweight material in transportation area. Warm forming is a forming method that improves formability and reduces springback. The magnesium alloy sheet has a characteristic that large difference of flow stress increases depending on strain rate at high temperature. These characteristics cause low dimensional accuracy of formed products. In this study, experiments were performed on the 2D-draw bending with respect to the temperature and forming speed in order to investigate the effects of strain rate and temperature. It was found that as the temperature increases, spinrgback of 2D-draw bending decreased and formability of AZ31B increased. Additionally, the effect of the punch speed was investigated. At 250°C, as the punch speed increased, the springback of 2D-draw bending decreased.