Zn-22%Al合金の時効による組織変化が常温塑性におよぼす影響

抄録

Aging characteristics of Zn-22%Al alloy at room and elevated temperatures were measured by structure observations and thermal analysis. The relationship between microstructure and tensile properties were as follows:
(1) The TTT curve of this alloy showed a typical C-curve. Lamellar microstructure appeared above 100°C, granular microstructure below 50°C and a mixed microstructure between the two temperature ranges. In addition, a superplastic phenomenon was observed in the presence of the granular microstructure, and the superplastic behaviour disappeared rapidly with the appearance of the lamellar structure.
(2) The tensile properties of this alloy were influenced by the aging time at room temperature after solution-treatment. The dissolution into two phases lasted about 20 min after water quenching, but the superplasticity was not observed within 1 hr because of the smaller grain size, and after 2 months these specimens showed a remarkable total elongation.
(3) This aging phenomenon showed that grains were grown with aging time, and their grain size which showed the maximum elongation was related to the strain rate; the faster the strain rate, the smaller the grain size which showed the maximum elongation and the smaller the total elongation.
(4) After the dissolution into two phases, the aging time was shortened by elevating the temperature, and the grain size showing the maximum elongation was equal to that in the case of aging at room temperature.