Effects of Ytterbium and Zirconium on precipitation evolution and coarsening resistance in aluminum during isothermal aging

• The aged Al–0.03Yb–0.06Zr alloy forms core-shell structured Al3(Yb,Zr) precipitates.
• The Al–0.03Yb–0.06Zr alloy obtains a maximum hardness of 485 MPa.
• The Al3(Yb,Zr) precipitates in Al–0.03Yb–0.06Zr have remarkable coarsening resistance.

The precipitation hardening and coarsening resistance of precipitates were studied in Al–Yb, Al–Zr and Al–Yb–Zr alloys during aging at 400 °C. The aged Al–0.03Yb–0.06Zr alloy forms core–shell structured Al3(Yb,Zr) precipitates and the core and shell of precipitates are enriched in Yb and Zr respectively. Due to the dense and core–shell structured Al3(Yb,Zr) precipitates, the Al–0.03 at%Yb–0.06 at%Zr alloy obtains a maximum hardness of 485 MPa, which is greater than that of the Al–0.03 at%Yb and Al–0.06 at%Zr alloys. The Al3(Yb,Zr) precipitates in Al–0.03 at%Yb–0.06 at%Zr have remarkable coarsening resistance with a time exponent for the average radius of precipitates 1/n = 0.19 ± 0.02, which is smaller than that for Al–0.03Yb (0.34 ± 0.01).