Mg-Al系合金とTiの高温濡れ現象

抄録

Magnesium alloy is expected as one of the environmentally benign materials for significant weight reduction of the components due to its high specific strength. It is, however, necessary to improve its Young's modulus when Mg alloys are applied to structural components. Ceramics hard particles are generally used as reinforcements to improve the stiffness of Mg matrix composite. However, they also cause the decrease of ductility of the composite materials. In the present study, pure Ti particles were used as reinforcement because they had enough ductility and high Young's modulus compared to Mg alloys. For the materials design of Mg matrix composites reinforced with Ti particles, the wetting behavior of Ti by the molten Mg alloy should be investigated to fabricate a good coherence at the interface between the matrix and dispersoids. The sessile drop test results showed an extremely good wettability between pure Mg and pure Ti due to a thermite reaction at the interface between Mg and TiO₂ surface films of the Ti substrate. The wettability between Mg-Al alloy (AZ80) and Ti was investigated in high-purity argon gas atmosphere at 1073K. In particular, the effect of Al element contained in AZ80 on the wetting behavior was examined. When AZ80 was dropped on the pure Ti plate (t=0s), the contact angle between the droplet and the Ti plate was 10°. The contact angle and the droplet height were gradually reduced with increasing time. Ti plate was completely covered with molten AZ80 in 60s. The result indicated the wettability of pure Ti by molten Mg-Al alloy was extremely good compared to the combination of pure Mg and pure Ti. When the specimen was kept at 1073K for 180s, Al was enriched on interface between AZ80 and Ti, but Al-Ti intermetallic compounds were not formed. It was concluded the wetting phenomenon of Ti by Mg alloy droplet reached termination before formation of Al-Ti intermetallics and Al element of AZ80 had no harmful effect on the wetting behavior between Mg alloy and Ti.