Effect of Cr on dynamic recrystallization behavior and mechanical properties of Al-Cu-Mg-Ag alloys

The effects of Cr on the microstructure of as-cast Al-Cu-Mg-Ag alloys and the distribution， size and number density of dispersoids after double-stage homogenization were investigated by OM， XRD， SEM-EDS and TEM methods. The effects of Cr on the dynamic recrystallization behavior of Al-Cu-Mg-Ag alloys under different equivalent strain were studied by high-throughput isothermal compression experiments. The results show that spherical Al7（Cr， Mn） dispersoids with average diameter and number density of 67.4 nm and 4.7 μm－2 are precipitated during the homogenization process， in addition to the rod-like T-Al20Cu2Mn3 dispersoids. The opposite equilibrium distribution coefficient of Cr and Mn （KMn<1 vs KCr>1） reduces the area fraction of dispersoid-free zones from 29.5% to 13.8%， the average length of rod-like T-Al20Cu2Mn3 decreases from 275.4 nm to 147.3 nm， and its number density increases from 3.5 μm－2 to 10.4 μm－2. EBSD and tensile test results indicate that the Al7（Cr， Mn） dispersoids hinder the dislocation movement， reducing the transition from low-angle grain boundaries to high-angle grain boundaries during thermal compression， and inhibiting the dynamic recrystallization. The addition of Cr increases the mechanical properties of Al-Cu-Mg-Ag alloys at different temperatures， and the yield strength contributions of Al7（Cr， Mn） dispersoids to the alloys at 25，250 ℃ and 300 ℃ are 21.9，16.2 MPa and 15.3 MPa， respectively.