Hardness measurements and electron microscopic observations were made to study factors affecting the aging of Mg-Zn alloy and Mg-Zn-(Ag) alloys. In regard to the homogeneous and heterogeneous nucleation in these alloys, direct aging, twostep aging and strain aging were carried out, with the results summarized as follows:the nucleation rate largely depends on the quenching rate, the concentration of zinc and the small amount of silver (0.04wt%).(2) In the C-curves which were obtained by plotting the incubation time against the reciprocal of the absolute aging temperature, the nose or the lower part of it gives an optimum condition for the pre-aging. As regards the direct aging and the observations show that these phases preferentially precipitate on dislocations and fine structures such as twin boundary and sub-boundary.

of electrical resistivity and hardness measurements, the X-ray Debye-Scherrer method and electron-microscopic observations. From the kinematic point of view the aging sequences were analyzed using the C-curve obtained by plotting the logarithm of the incubation time as a function of the reciprocal of the absolute aging temperature.The results showed that the tion of G. P. zones.

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