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

1.对于纯Al、Al-3%Mg、Al-0.2%Zr、Al-0.2%Sc、Al-3%Mg-0.2%Sc和Al-5.5%Mg-2.2%Li-0.12%Zr合金，通过ECA压制分别获得1.2、0.3、0.7、0.7、0.2和1.2 μ m的细晶粒尺寸。细晶粒是稳定的，直到473 K的纯Al和Al-3%Mg合金。Al-0.2%Zr合金在573 K仍保持细晶的热稳定性。Al-0.2%Sc合金和Al-3%Mg-0.2%Sc合金在673 K的高温下仍保持稳定性。含Zr或Sc的Al合金中的细晶比纯Al和Al-3%Mg合金中的细晶在更高的温度下保持稳定的原因归因于细分散的Al_3Zr和Al_3Sc颗粒的存在。Al_3Sc比Al_3Zr更能有效地抑制铝合金的再结晶。对于Al-5.5%Mg-2.2%Li-0.12%Zr合金，在673 K时仍保持细晶.对于Al-3%Mg合金，Hv=46+ 35 d ^<-1/2>（其中Hv是维氏显微硬度，d是平均晶粒尺寸）的Hall-Petch关系在晶粒尺寸为0.2至100 μ m的范围内是有效的。另一方面，对于Al-5.5%Mg-2.2%Li-0.12%Zr合金，Hv=75+ 27 d ^-1/2>的Hall-Petch关系在2至60 μ m的晶粒尺寸范围内是有效的。Al-3%Mg-0.2%Sc合金在673 K和3.3 × 10 ~（-3）s ~（-1）条件下的断裂伸长率为1030<-2><-1>。Al-5.5%Mg-2.2%Li-0.12%Zr合金在623 K和10 ~（-1）S ~（-1）条件下的断裂伸长率为1200%<-2><-1>。断裂区的晶粒尺寸大于夹持区的晶粒尺寸。这表明在高温拉伸试验过程中发生了应力诱导的晶粒生长。

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.