Microstructure evolution and high-temperature performances of AA6111 alloy strengthened by core-shell structured Al3(Sc, Zr) nanoprecipitates

In this paper, microstructure and tensile performances at elevated temperature were investigated in detail. The results showed that significant grain refinement was obtained with Sc, Zr modification. Coarse AlFeSi intermetallics distributed along grain boundaries were refined to small pieces. During hot extrusion, DRV and DRX progress was accelerated by Al3(Sc, Zr) precipitates via hindering movement of dislocations. Besides, Al3(Sc, Zr) could also limit coarsening of recrystallized grains during subsequent heat treatment and high-temperature tensile testing. Nanosized Al3(Sc, Zr) precipitates ranging from 20 to 80 nm showed excellent coarsening resistance, which was attributed to its special core-shell structure that Zr-enriched outer shell with sluggish diffusivity could act as a diffusion barrier and hinder diffusion of inner Sc-enriched core at high temperature. For both AA6111 and AA6111-0.2Sc-0.1Zr alloys tensile tested at 200 °C, 250 °C and 300 °C, their strength was all decreased with the rising of temperature. But the performances of AA6111-0.2Sc-0.1Zr alloy were always higher than that of AA6111 matrix alloy at any temperature.