The Effect Of Yb And Si On Precipitation Behaviour Of Al-Zr Alloys During Aging

Al₃Zr precipitates of Al-Zr binary alloy during aging exhibit kinetics stability at elevated temperature,thereby performing outstanding heat resistance,precipitation strengthening as well as recrystallization resistance.However,lower diffusion rate of Zr in?-Al leads to its incomplete precipitation,while solute Zr atoms evidently decrease electrical conductivity of Al-Zr alloys.Simultaneously,uneven distribution of precipitated Al₃Zr in?-Al and lower density of L1₂ structured Al₃Zr influence high-temperature creep resistance and recrystallization resistance.Microalloying element Yb has been proved effective in enhancing high-temperature performance of Al-Zr alloys;meanwhile,being a common element in commercial-purity aluminium,Si evidently improves precipitation strengthening in Al-Zr alloys.Effects of Yb,Si additions to Al-0.08Zr?at.%?alloys are investigated herein to study the high-temperature aging properties and precipitation behaviors.Combined measurements involving Vickers microhardness,electrical conductivity,scanning electron microscope?SEM?,transmission electron microscope?TEM?and three dimensional atom probe?3DAP?are employed to study precipitation behavior of Al-0.08Zr-0.03Yb?at.%?,Al-0.08Zr-0.10Si?at.%?,Al-0.08Zr-0.05Si-0.015Yb?at.%?and Al-0.08Zr-0.10Si-0.03Yb?at.%?,as well as mechanism of Si and Yb atoms during aging.The result confirms that combination of Yb and Si effectively enhances precipitation behavior of Al-Zr alloys,and the addition of0.10at.%Si further decreases Yb solubility in Al-Zr,with a decline in Yb concentration in Al-matrix from 0.0112at.%to 0.0084at.%.Therefore,the composition of alloy could be optimized as Al-0.08Zr-0.10Si-0.03Yb?at.%?.Meanwhile,Yb and Si both accelerate aging precipitation of Al-Zr alloys,whereas they share different mechanism.Yb displays a diffusion rate four orders of magnitude larger than Zr in?-Al at 400oC,Yb disperses preferentially at 15min,forming L1₂-structured Al₃Yb at 1h as the heterogeneous nuclei for Al₃Zr.Small Si addition evidently accelerates diffusion rate of Zr in Al-matrix,with incubation period of Al₃Zr precipitates decreased to 2h.Thus,the coarsening rate of Si-containing precipitates is significantly higher than that of Si-free precipitates,while the former average radius at the peak is two times of the latter one,leading to a decline in coarsening-resistance.In?Al,Si?₃(Zr_1-xYb_x)precipitates,Yb presents an inclination of segregation into the core,and it has a much lower concentration of 1at.%.Zr distributes evenly in the Al-matrix with a concentration of 27at.%,while Si shows slight segregation at the interface of precipitate and Al-matrix.There is no obvious core/shell structure in?Al,Si?₃(Zr_1-xYb_x)precipitate.