New insights into the effects of Sc/Zr addition on heat-resistant Al-8Ce alloy

The effects of the Sc and Zr co-addition on the microstructure and properties of the Al-8Ce alloy during casting, aging, and heat exposure process were investigated. The results show that the Sc and Zr co-addition changes the primary alpha-Al of Al-8Ce alloys from coarse dendritic to fine rounded, and its eutectic Al11Ce3 phase from coarse lamellar to fine short rods, which improves the stability of the microstructure. The high-temperature mechanical properties of Al-8Ce alloys were significantly increased by the Sc and Zr co-addition. The ultimate tensile strengths of Al-8Ce-Sc-Zr alloy at 250 and 350 degrees C were 213 and 143 MPa, respectively, which were 2.9 and 4.3 times that of Al-8Ce alloy, respectively. This was mainly due to the heterogeneous nucleation to primary alpha-Al and adsorption poisoning to eutectic Al11Ce3 phases caused by the microalloying of the Sc-Zr elements. And aging treatment after cold drawing promoted the formation of Al3(Sc, Zr) coherent nano-precipitates in the Al matrix, providing significant precipitation strengthening. The heat stability of Al-8Ce alloys was enhanced by the Sc and Zr co-addition. After heat exposure at 350 degrees C for 100 h, the hardness values of the as-cast Al-8Ce and aged Al8Ce-Sc-Zr alloys were 32.9 and 95.9 HV1, respectively, which represented slightly decreases of 17.3 % and 14 % compared with that before heat exposure. The superior thermal stability of Al-8Ce-Sc-Zr alloy was due to the presence of Sc and Zr atoms in the eutectic Al11Ce3 phase in the form of doping and the adsorption effect at the interface, which effectively inhibited the coarsening rate of the eutectic Al11Ce3 phase. This study provides valuable data support for the further application of aluminum-cerium alloys in the field of high-strength and heat-resistant aluminum alloys.