難燃性マグネシウム合金の摩擦攪拌継手の疲労特性調査とその改善

抄録

The purpose of this study was to investigate the fatigue properties of friction stir welded (FSW) joints of flame-retardant magnesium alloy (AZX 611) and to examine the effect of improving fatigue properties by zirconia shot peening treatment. The specimens were taken from the FSW joints plates so that the welding center and specimen center coincided. After sampling, the tool marks by FSW were removed by machining. The SP treatment was carried out with a zirconia shot (B 120) having a particle diameter of 0.12 mm. Fully reversed (R = -1) plane bending fatigue test were carried out using the base metal (BM) specimen, surface finished FSW joints (FSW-f) specimen and SP treated specimen. Surprisingly, the fatigue strength at 2×10⁷ cycles of the FSW-f was improved by about 15 MPa over of the BM specimen, and the fatigue life was also extended. The factor of fatigue property improvement of the FSW-f specimen was work hardening on the surface of the specimen when machining at the time of removal of tool marks. With this machining, high level compressive residual stress and surface hardening were induced to specimen. And then, fatigue property of BM specimen and FSW-f specimen were improved by the SP treatment. For the BM specimen, SP treatment could improve the fatigue strength and fatigue life property by peening effect. On the other hand, for the FSW-f specimen, only fatigue strength at 2×10⁷ cycles was improved.