Effect of rare earth element Er on the microstructure and properties of highly alloyed Al-Zn-Mg-Cu-Zr-Ti alloy

Abstract

By using standard melting casting, homogenization, extrusion, solid solution, and T6 aging, an Al-11Zn-3.1Mg-1.2Cu-0.2Zr-0.16Ti alloy was created, and the microstructure and mechanical properties of the alloy with various Er contents were investigated. The inclusion of Er promoted the increase in the number density and volume fraction of L12-Al3(Er, Zr) in the alloy, which greatly reduced the alloy's tendency to recrystallize, raised the internal dislocation density, and helped the alloy achieve grain refinement. To a certain extent, a moderate amount of Er added to the alloy may have helped the precipitation and phase transformation of precipitates. When the Er concentration rose from 0.15 to 0.45 wt.%, the refining effect and the density of L12-Al3(Er, Zr) were less influenced, but excessive Er interacted with other elements to form coarse intermetallic compounds, leading to the deterioration of mechanical properties. The yield strength (YS) and ultimate tensile strength (UTS) of the alloy grew first and then declined and flattened as the Er content increased from 0 to 0.45 wt.%, according to the mechanical properties test. All alloys with Er microalloying had superior elongation due to the decrease of number of high-angle grain boundary (HAGB). The optimal mechanical properties were shown in the 0.15 wt.% Er alloy, with a YS of 771.7 MPa, a UTS of 785.9 MPa, and an elongation of 9.5%.