Role of Yb and Si on the precipitation hardening and recrystallization of dilute Al-Zr alloys

The effect of Yb and Si on precipitation hardening and recrystallization of Al-Zr alloys have been investigated. The results show that Yb is more effective than Si to accelerate the precipitation kinetics and stimulate the precipitation of Al-Zr alloy. The peak hardness values for the Al-Yb-Si-0.08Zr are 510 MPa and 515 MPa after isochronal aging to 425 °C and isothermal at 350 °C for 200 h, respectively, which are significantly larger than that of the Al-Yb-Zr and Al-Si-Zr alloys. The precipitates in alloys with addition of Zr are more thermally stable than that of the Al-Yb alloy. The recrystallization temperatures of Al-Zr, Al-Si-Zr, Al-Yb-Zr and Al-Yb-Si-Zr alloys are 250, 400, 425 and 450 °C, respectively, increase with the increase of the corresponding peak aging hardness. The recrystallization temperature of Al-Yb alloy is 325 °C, which is much lower than that of the Al-Yb-Zr alloy due to the coarsening of the Al3Yb at temperature larger than 300 °C.