Mg-5.5 wt%Zn合金の時効におよぼす銀の影響

抄録

Hardness measurements and electron microscopic observations were employed to study the effects of additions of 0.04 and 0.13 wt% silver on the direct aging and the two-step aging characteristics of Mg-5.5 wt%Zn alloys. The aging processes are changed by the intersection temperatures of 100°C and about 50°C, which are obtained from the C-curves analyzed kinematically, but the silver addition raises these temperatures by 10°∼20°C. The final hardening is due to the genaral precipitation of the transition phase β′ in the form of a long thin rod. This system indicates the quenching rate dependence and effectiveness of the two-step aging; the pre-β′ region in the C-curve diagram gives the optimum condition of pre-aging, and the addition of 0.04 wt% silver is most suitable for these phenomena. Electron microscopic observations show that the silver addition little affects the direct aging, but it accelrates the refinment of the β′ phase in the two-step aging. As regards the direct aging and the two-step aging, it may be concluded that the silver atom plays a significant role as a positive action of nucleation for the pre-β′ or the β′ phase.