Effect of Zr and Sc micro-additions on the microstructure and mechanical properties of as-cast Al-5Ce alloy

To improve the strength and decrease segregation of Al-Ce alloys, the effect of micro-addition of 0.2Zr, 0.2Sc and combined addition to Al-5Ce alloys are explored through gravity casting. The addition of Zr and Sc decreases the grain size from 1320 mu m to 495 mu m and 710 mu m, respectively, and combined addition exhibits the minimal grain size of 290 mu m Al11Ce3 phase is first observed from lamellar to short rods structure by adding Zr. After heat treatment, 0.2Sc and 0.2Zr+0.2Sc additions form Al3Sc and Al3(Sc,Zr) nanoscale precipitates, whose average radii are 3.2 nm and 1.5 nm, in the Al matrix respectively. The 0.2Zr addition leads to outstanding elongation of 23%, while 0.2Sc addition dramatically improves the yield strength from 49 MPa to 155 MPa after T5 heat treatment. Combined addition owns the best yield strength of 156.5 MPa among other Al-5Ce alloys. These coherent nano-precipitates providing 68% yield strength act as effective reinforcement at ambient temperature. The main strengthening of Al3Sc is the Orowan looping mechanism, while the anti-phase boundary strengthening plays the main role for Al3(Sc,Zr) precipitates.