アルミニウムおよびその合金におよぼすジルコニウムの効果(第4報)

ZrAl₃の析出現象およびAl-Zr合金の再結晶温度におよぼすSi,Mgの機構

抄録

In the report No. 3, it was stated that when the rapidly solidified Al-Zr alloy is treated by prceipitation method, the effect of zirconium on elevation of recrystallization temperature is particularly remarkable.
It is considered that this phenomenon is due to the fact that the recrystallization is remarkably prevented by fine ZrAl₃ which is precipitated from the supersaturated solid solution of Al-Zr alloy. It is very difficult, however, to observe the precipitation of ZrAl₃ by microscope. That is why, in the report No. 3, it was examined by the measurement of the electric resistance.
In this report, the precipitation was examined by means of X-ray diffraction analysis, and also, the mechanism of Si and Mg on the recrystallization temperature of Al-Zr alloy was examined.
The findings are summed up as follows:
1. From the X-ray diffraction analysis, it was more clearly confirmed that zirconium added to aluminium becomes supersaturated solid solution through rapidly cooled solidification phenomenon and, when the preciptation treatment is given, it is precipitated as ZrAl₃ in very fine form.
2. The mechanism of Si on the recrystallization temperature of Al-Zr alloy was found out as follows: When rapidly cooled solidification is given to the alloy, Si decreases solubility of zirconium into aluminium, and zirconium precipitates as the form of Zr₅Si₃. In this case, however, as a certain amount of zirconium dissolves into aluminium, the effect of zirconium is not remarkably prevented. But, when the precipitation treatment is given, the effect is remarkably prevented, because the precipitation of zirconium as the form of Zr₅Si₃ it more promoted.
3. The mechanism of Mg on the recrystallization temperature of Al-Zr alloy was found out as following: When precipitation treatment is given, ZrAl₃ becomes hard to precipitate and, therefore, the effect of zirconium is not remarkable as in the case that Zr precipitate in the fine form of ZrAl₃. Mg does not work so much as Si in the precipitation treatment.
4. Si and Mg increase the recrystallization rate of Al-Zr Alloy to which the precipitation treatment is given, But they make grain size finer because they remarkably increase the nucleation rate.