In Al-Zn-Mg alloy, hydrogen leads to degradation of mechanical properties. It is indispensable to suppress this phenomenon called hydrogen embrittlement (HE) for increasing the strength of Al-Zn-Mg alloy. Intergranular fracture (IGF) mainly occurs when HE affects this alloy. In order to suppress HE, we need to understand the initiation behavior of IGF. Heterogeneous distribution of stress, strain and hydrogen concentration in polycrystalline material have an influence on the IGF initiation. In the present study, distribution of stress, strain and hydrogen concentration in actual fractured regions were investigated by employing a crystal plasticity finite element method and hydrogen diffusion analysis using a 3D-image-based model. This model was created based on 3D polycrystalline microstructure data obtained from X-ray imaging technique. By combining in-situ observation of tensile test of the same sample by X-ray CT with the simulation, we compared distribution of stress, strain and hydrogen concentration with actual crack initiation behavior. Based on this, the condition for intergranular crack initiation were discussed. As a result, it is revealed that stress load perpendicular to grain boundary induced by crystal plasticity dominate intergranular crack initiation. In addition, accumulation of internal hydrogen induced by crystal plasticity had little impact on crack initiation.

High thermal conductivity ternary Mg alloys composed of Zn and Y pair with a negatively high mixing enthalpy was developed by optimization of alloy composition and heat-treatment conditions. Optimal alloy composition was Mg-1.88Zn-0.75Y (at%) alloy, in which the ratio of Zn content to Y content was 2.5 and the Y content was 0.75 at%. The alloy was composed of α-Mg＋W phase (Mg₃Zn₃Y₂）＋I phase (icosahedral Mg₃Zn₆Y). Heat treatment under the optimal heat treatment conditions, where temperature, time and cooling rate were 633 K, 15 h and air cooling, respectively, improved the thermal conductivity from 114 to 141 Wm^‒1K^‒1 that corresponds to 90% of the pure Mg thermal conductivity. Fine W phase precipitation in α-Mg matrix by the heat-treatment caused a reduction of solute Y element in α-Mg matrix, resulting in improvement of the thermal conductivity.

In this study, we aim to address the dominant microstructural parameter of the high strength of Al-Fe alloy components additive-manufactured by the laser powder bed fusion (L-PBF) process. This study systematically investigated the compression response of single-crystal micropillars with a fixed diameter of approximately 3μm prepared on the surfaces of the L-PBF built Al-2.5%Fe binary alloy sample, and the subsequently heat-treated samples (300°C and 500°C), together with the slowly solidified Al-2.5%Fe alloy sample for comparison. The single-crystal micropillars of the L-PBF built sample exhibited a high yield strength of approximately 250 MPa and pronounced strain hardening. The compressed single-crystal specimens exhibited a uniform deformation indicating the activated multi-slip systems. Such a trend was observed in the 300°C heat-treated sample. However, the relatively low yield strength and strain hardening rate were found in single-crystal micropillars of the 500°C heat-treated sample as well as the slowly solidified sample. In the compressed micropillars, a single-slip system was dominantly activated. These results indicated that numerous nano-sized Al₆Fe-phase particles (contained in the specimens of the L-PBF built sample and the 300°C heat-treated sample) could contribute to high yield strength and the enhanced activation of multi-slip systems resulting in the pronounced strain hardening.

The active deformation mode (slip systems and twinning) of extruded AZ31B alloy (Mg-3Al-1Zn, mass%) during compression at RT, 100°C and 150°C was investigated by visco-plastic self-consistent (VPSC) simulation. Compression tests were first performed to obtain compression curve of AZ31B. The VPSC model was fitted to the compression curves to estimate the Voce hardening parameters which are required for the VPSC simulation. In the case of compression along the extrusion direction, work-hardening occurred rapidly with the transition of dominant deformation modes at all temperatures. In the case of compression to the other directions, basal＜a＞slip was dominant throughout the deformation at all compression temperatures. In addition, prismatic＜a＞slip and tensile twin were active in the early stage of deformation, and pyramidal＜c＋a＞slip became active in the later stage of deformation. Pyramidal＜c＋a＞slip became more active with increasing temperature from RT to 100°C, whereas basal＜a＞nd prismatic＜a＞slips became more active with increasing temperature from 100°C to 150°C. These different trends in the change of the active slip system with increasing temperature can be attributed to the CRSS maximum of the pyramidal＜c＋a＞slip located around 100°C.