| Research Abstract |
1. Fine grain sizes of 1.2, 0.3, 0.7, 0.7, 0.2 and 1.2 mum were obtained by ECA pressing for pure Al, Al-3% Mg, AI-0.2% Zr, A1-0.2% Sc, A1-3% Mg-0.2% Sc and A1-5.5% Mg-2.2% Li-0.12% Zralloys, respectively. Fine grain was stable up to 473 K both for pure Al and AI-3% Mg alloys. On the other hand, the thermal stability of fine grain was kept up to 573 K for AI-0.2% Zr alloy. Furthermore, the stability both for AI-.0.2% Sc and AI-3% Mg-0.2% Sc alloys was preserved up to a temperature as high as 673 K.The reason why fine grain in the Al alloys containing Zr or Sc is stable up to higher temperature than that in the pure Al and Al-3% Mg alloy is attributed to the existence of fine-dispersed AI_3Zr and Al_3Sc particles. And the Al_3Sc is more effective than AI_3Zr to inhibit recrystallization in Al alloys. For the AI-5.5% Mg-2.2% Li-0.12% Zr alloy, fine grain was kept up to 673 K.
2. For the AI-3% Mg alloy, the Hall-Petch relationship of Hv=46+35d^<-1/2> (where Hv is Vickers microhardness and d is average grain size) was valid in the range of grain size of 0.2 to 100 mum. On the other hand, for the AI-5.5% Mg-2.2% Li-0.12% Zr alloy, the Hall-Petch relationship of Hv=75+27d^<-1/2> was valid in the range of grain sizes of 2 to 60 mum.
3. Elongations to failure was 1030 in the testing condition of 673 K and 3.3x10^<-2> s^<-1> for A1-3% Mg-0.2% Sc alloy On the other hand, the elongation was 1200% in the testing condition of 623 K and 10^<-2> S^<-1> for Al-5.5% Mg-2.2% Li-0.12% Zr alloy. Grain size in the fracture region was larger than that in the gripped region. This indicates that grain growth induced by stress takes place during tensile testing at elevated temperatures.
|
