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-MgAg alloys under different equivalent strain were studied by high-throughput isothermal compression experiments. The results show that spherical Al-7(Cr, Mn) dispersoids with average diameter and number density of 67.4 nm and 4. 7 mu m(-2) are precipitated during the homogenization process, , in addition to the rodlike T-Al20Cu2Mn3 dispersoids. The opposite equilibrium distribution coefficient of Cr and Mn (K-M n <1 vs K-Cr> 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 <mu>m(-2) to 10. 4 mu m(-2). EBSD and tensile test results indicate that the Al-7(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 Al-7(Cr, Mn) dispersoids to the alloys at 25,250 ,250 degrees C and 300 degrees C are 21. 9,16. ,16. 2 MPa and 15. 3 MPa, respectively.