The effects of SiC particles on the morphologies, microstructures, and mechanical properties of tungsten inert gas welded AZ31 magnesium alloy joints with TiO 2 flux coating were studied. The results showed that an increase in the amount of the TiO 2 coating improved the weld penetration and the depth/width (D/W) ratio of the TIG welded AZ31 magnesium alloy seams. The a-Mg grains of FZ of welded joints refined gradually with the addition of micro-sized SiC (<30%) =nano-sized SiC (<40%) particles in coatings, and then coarsened when more SiC particles added. In addition, the microhardness of the FZ and ultimate tensile strength of the welded joints increased with the addition of SiC particles, and nano-sized particles have more strong efficiency on the improvement of mechanical properties compared with micro-sized SiC particles.
In order to study the effect of loading mode on fatigue properties of high speed steel (0.7C-4Cr-0.1W-3 Mo-2V) in very high cycle regime, fatigue tests under axial loading and rotating bending condition were performed in laboratory air using the hourglass shaped specimen. From the experiment results, clear duplex S-N curve appeared in both loading conditions, that is, there were two curves composed of a surface failure mode and a subsurface failure mode. Fatigue life under axial loading condition was shorter than that under the rotating bending condition, especially in low stress amplitude level. The difference in fatigue lifetime and transition of failure mode between the loading modes was discussed from the viewpoint of inclusion size, applied stress distribution across the specimen section and residual stress in surface layer.
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