Effect of Al3(Sc,Zr) Particles on Tensile Properties of an Al-Zn-Mg-Cu-Sc-Zr Alloy

Small additions of Sc and Zr may considerably improve both strength and ductility of 7000 series aluminum alloys, which is associated with precipitation of fine coherent Al3(Sc,Zr) particles. These particles also increase resistance to recrystallization and promote formation of a stable refined microstructure. Because of very low equilibrium solubility of Sc and Zr in Al alloys, a supersaturated solid solution of these elements in the Al matrix presented after casting is responsible for precipitation of the Al3(Sc,Zr) particles during subsequent heat treatment, while the strengthening effect depends on the particle size and number density. Therefore, it is necessary to optimize precipitation of the Al3(Sc,Zr) particles, in order to achieve superior balance of mechanical properties. In the present work, the effect of heat treatment conditions on microstructure and tensile properties of a developmental 7000 series Al alloy SSA018 modified with Sc and Zr was studied, with special emphasis on the analysis of size and number density of the Al3(Sc,Zr) particles, and their effect on the strength increase.