Study on Phases Formation and Modification Ability of Rare Earth Elements La, Ce, Sm and Er in Al-Zn-Mg-Cu-Zr Alloy

In this paper, the effects of different rare earth elements (La, Ce, Sm and Er) on the microstructure and mechanical properties of Al-6.7Zn-2.6 Mg-2.0Cu-0.1Zr alloys have been investigated. The results show that the addition of rare earth elements, especially those with a higher atomic number (La < Ce < Sm < Er), could effectively reduce the alloy grain size. Rare earth elements form Al11La3, Al4Ce, Al10Cu7Sm2 and Al8Cu4Er phases in the alloy. After being rolled, the small rare earth phases could pin the grain boundaries, inhibit recrystallization, and refine the structure during solid solution treatment. Moreover, the rare earth atoms would provide more nucleation sites for the precipitation of the eta' phase to make it smaller during the aging treatment. Therefore, the rare earth elements can significantly improve the mechanical properties of the alloy through grain refinement and precipitation strengthening. Because Er has a lower solid solubility in Al matrix than other elements, and can form Al-3 (Er, Zr) phase, this phase can effectively inhibit recrystallization behavior. Therefore, among all the studied rare earth elements, Er has the strongest strengthening effect, which increases the tensile strength and yield strength of the alloy by 40Mpa and 29Mpa, respectively. The Sm-containing alloy acquire more fine recrystallized grains after solid solution, so that the elongation of the alloy is increased to 14.3%, and its plasticity is the best.

Automated summary

Rare earth elements can significantly improve the mechanical properties of the alloy through grain refinement and precipitation strengthening. Among the studied elements, Er has the strongest strengthening effect, significantly increasing the tensile strength and yield strength of the alloy. Additionally, alloys containing Sm exhibit the best plasticity due to the fine recrystallized grains obtained after solid solution treatment.