Microstructural Stability and Hall-Petch Relationship for Fine-Grained Alloys Fabricated by ECAP

1. 对纯Al、Al-3% Mg、AI-0.2% Zr、A1-0.2% Sc、A1-3% Mg-0.2% Sc和A1-5.5% Mg-2.2% Li-0.12% zr合金进行ECA压制，得到的晶粒尺寸分别为1.2、0.3、0.7、0.7、0.2和1.2 μ m。纯Al和AI-3% Mg合金在473 K高温下均保持稳定的细晶粒。另一方面，AI-0.2% Zr合金在573 K高温下保持了细晶粒的热稳定性。此外，AI- 0.0.2% Sc和AI-3% Mg-0.2% Sc合金在高达673 K的温度下仍保持稳定性。含Zr或Sc的铝合金比纯Al和Al-3% Mg合金在更高温度下晶粒稳定的原因是AI_3Zr和Al_3Sc颗粒的存在。Al_3Sc比AI_3Zr更有效地抑制了铝合金的再结晶。AI-5.5% Mg-2.2% Li-0.12% Zr合金的晶粒保持在673 K.2以下。对于AI-3% Mg合金，Hv=46+35d^<-1/2>（其中Hv为维氏显微硬度，d为平均晶粒尺寸）的Hall-Petch关系在0.2 ~ 100 μ m晶粒尺寸范围内成立。另一方面，对于AI-5.5% Mg-2.2% Li-0.12% Zr合金，Hv=75+27d^<-1/2>的Hall-Petch关系在2 ~ 60 μ m晶粒尺寸范围内成立。而Al-5.5% Mg-2.2% Li-0.12% Zr合金在623 K和10^<-2> s^<-1>试验条件下的延伸率为1200%，在673 K和3.3 × 10^<-2> s^<-1>试验条件下的延伸率为1200%。断口区晶粒尺寸大于夹持区晶粒尺寸。这表明在高温拉伸试验中，应力诱导晶粒长大。

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.