Synchrotron radiation small-and wide-angle scattering measurements have been performed for Mg 98.6 Y 1 Zn 0.4 alloys. In the early stage of phase transformation from supersaturated solid solutions, isotropic scattering suggesting segregation at grain boundaries was observed. It grew with temperature during heating the sample at a constant rate of 0.133 K/s. Above 600 K where introduction of stacking faults is expected, needle-like scattering became visible, which represents platelet shape segregation of cluster layers called cluster arranged layer (CAL). The layer eventually developed to form multiple layers, cluster arranged nano plates (CANaP) at higher temperatures. Microstructure change by hot rolling after the heat treatments has been examined from a viewpoint of kink-deformed microstructures.

The present study investigated the hydrogen-related fatigue fracture under various test frequencies in low-carbon martensitic steel. In the hydrogen-charged specimen, although the number of cycles to failure decreased with decreasing test frequency, the time to failure was almost the same regardless of the test frequency. Observation of fracture surface revealed that the transgranular surface was a main component in the uncharged specimen, while the intergranular surface was often observed especially at the lower test frequency in the hydrogen-charged specimen. In addition, for the transgranular fracture, cracks often propagated across the laths regardless of test conditions. The high-strained region was observed over a relatively wide area in the uncharged specimen. On the other hand, the hydrogen-related fatigue-crack propagation was accompanied by intense localized plastic deformation, which could accelerate crack growth. The intergranular