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The solidification paths of Al-Zn-Mg alloys in the Al-rich corner were investigated. The thermodynamic data for the calculation are obtained by direct coupling with the CALPHAD software Thermo-Calc via its TQ6-interface and the COST2 database. The influences of the initial compositions and the extent of solid back diffusion on the solidification path were numerically investigated by sample calculation of the ternary Al-Zn-Mg alloys. The calculation results of solidification paths of the selected alloys: Al-5Zn-3Mg (in wt.%), Al-5Zn-10Mg, Al-2.5Zn-15Mg, Al-10Zn-20.5Mg, Al-8Zn-25Mg, were: L→(L+α-Al), L→(L+α-Al)→(L+α-Al+TAU), L→(L+α-Al)→(L+α-Al+AlMg_β), L→(L+α-Al)→(L+α-Al+TAU)→(L+α-Al+TAU+AlMg_β), L→(L+α-Al)→(L+α-Al+AlMg_β)→(L+α-Al+TAU+AlMg_β), respectively. The results show that the initial compositions and the extent of solid back diffusion have a great influence on solidification path, and the amounts of eutectic phase increase with the decrease of the solid back diffusion coefficient. The equilibrium solute partition coefficients for Zn and Mg in alloys are also calculated and their influence on micro-segregation in the primary solidification of Al-5Zn-10Mg alloy is analyzed. |
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