Improving The Strength/toughness Of Super-high Strength Aluminum Alloys By Alloying

With the development of aerospace industry and the increase of people’s living standard, property requirement of aluminum alloys increase constantly. Therefore, the need for new alloys has become more and more strong. In this paper, By using optical microscopy (OM), x-ray diffraction spectrometry (XRD), electronic probe microanalysis (EPMA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), tensile test and micro-hardness test, the effect of alloying to Al-Zn-Mg-Cu-Zr alloy on mechanical properties and microstructure are studied.After adding Gd, the microstructures of as-cast Al-Zn-Mg-Cu-Zr alloys are significantly refined. The alloys will form dispersed Al3CuGd phase, which can strongly pin dislocations and subgrain boundary, inhibiting further recrystallization. The micro-segregation of the Al-Zn-Mg-Cu-Zr alloy can be significantly reduced, the relative intracrystalline solubility of Zn, Mg and Cu elements could be improved and the strength and elongation of T6state could be significantly improved after adding Gd. The addition of Gd extended the peak-aging time, made the peak-aging arriving earlier and improved the peak-aging hardness of artificial age-hardening at120℃. The alloy got the optimum performance when the alloy containing0.25%Gd. Excessive Gd addition increased the amount of non-equilibrium eutectic phases and depleted major alloying elements. The present non-equilibrium, were detrimental to comprehensive mechanical properties.The combined properties of the Al-Zn-Mg-Cu-Zr-0.25%Gd alloy could be harmed reduced after adding Y only. But the combined additions of Gd and Y to the Al-Zn-Mg-Cu-Zr alloys could obtain comprehensive mechnical properties. The experimental results demonstrate that:(1) After adding Gd or both with Gd and Y, the microstructures of as-cast Al-Zn-Mg-Cu-Zr alloys were significantly refined. Compared with non-RE addition, the alloys would form dispersed Al3uGd phase, which could strongly pin dislocations and subgrain boundary, inhibiting further recrystallization. The inhibition recrystallization effect was more obvious when adding0.25%complex Gd and Y.(2) The micro-segregation of the Al-Zn-Mg-Cu-Zr alloy could be significantly reduced after adding Gd only or both with Gd and Y. Meanwhile, the grain relative solid-solubility of Zn, Mg and Cu elements could be improved, that was:from54.82%,49.63%,26.38%to69.78%,78.75%,42.19%after adding0.25%Gd, and to71.74%,77.62%,51.23%with0.25%combined Gd and Y.(3) It was similar to the effect of artificial aging that adding single Gd or composite Gd and Y, which both could accelerate the peak aging time, improve the peak hardness, and extend the duration of peak aging time.(4) Compared with Al-Zn-Mg-Cu-Zr alloy, the alloys with Gd or with Gd and Y could significantly improve the strength and elongation of T6state. When adding0.20%compound Gd and Y elements, the best strength was tensile strength was648.9MPa, yield strength was634.1MPa and the best elongation was16.8%with0.25%combined Gd and Y.