Effects of Zr-addition on intergranular fracture of Al-Cu-Mg and Al-Zn-Mg-Cu alloys

Abstract

Effects of Zr addition on the intergranular fracture of Al-Cu-Mg and Al-Zn-Mg-Cu alloys were investigated. The alloys were Al-4.6 mass%Cu-1.5 mass%Mg (0.17 mass%Zr) and Al-7.5 mass%Zn-2.9 mass%Mg-2.0 mass%Cu (0.2 mass% Zr). All alloys were synthesized using high-purity aluminum with more than 99.999 mass%. The grain size and hardness of each alloy were made consistent by annealing and further aging treatment, respectively. It was revealed that the Zr addition suppresses intergranular fracture and improves the ductility under the condition that the grain size and hardness are the same. These effects of Zr addition appeared near the transition region from transgranular fracture to intergranular fracture. The first-principles calculation results indicated that Zr is the only element which segregates to the grain boundary and strengthens the grain boundary among alloying elements of Zn, Mg, Cu, and Zr in aluminum.