Relation between low temperature ageing processes and compositions of (α+T) type Al-Zn-Mg alloys:Mainly, Studies on measurements of electric resistivity
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The relation between the ageing processes at low temperatures and compositions of two-phase (α+T) Al-Zn-Mg alloys were studied at 051°C mainly by electric resistivity measurements and also by hardness measurements and transmission electron microscopy. Ten sorts of alloys, having different total amounts of solutes and different Zn/Mg ratios were prepared for specimens. Such factors as quenching and ageing temperatures and quenching rate were different in each specimen.Principal results obtained were as follows:(1) The initial ageing rate increased with increasing total amount of solutes, and it also increased with increasing Zn/Mg ratio among the specimens of the same content of (Zn+Mg) at.%. On the other hand, the slow reaction rate was lower for the specimens of higher Zn/Mg ratio. The binding energy between a vacancy and a Mg atom was supposed to be less than as expected.(2) In each specimen, the quenching temperature had little effect on the initial ageing rate, but the slow reaction rate was lower with the rise of quenching temperature.(3) Air cooling from the quenching temperature resulted in only the mere decrease of the initial ageing rate in every specimen as compared with the normal quenching. However, the rate in the latter stage remarkably increased. It was confirmed that precipitates were formed during the air cooling in every specimen, and their quantity was larger in the specimens of higher Zn/Mg ratios and higher contents of (Zn+Mg).(4) The ageing behavior of these alloys would be explained as follows.Assuming that the interaction between two solutes is negligibly little, the diffusivity of Zn atoms is very greater than that of Mg atoms. Therefore, the migration of Zn atoms leading to the formation of clusters (rich in Zn) had effects on the process of initial ageing, particularly in the alloys rich in Zn. However, the migration of Mg had effects on the process of the latter ageing. It is out of question that the supersaturation of alloys had effects on the ageing process.
- 一般社団法人 軽金属学会の論文
一般社団法人 軽金属学会 | 論文
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