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Deng Y.,Central South University | Yin Z.,Central South University | Zhao K.,Central South University | Duan J.,Central South University | And 2 more authors.
Corrosion Science | Year: 2012

Sc and Zr microalloying additions and increasing aging time at 120°C both can effectively improve the corrosion resistance of Al-Zn-Mg alloys. The low corrosion susceptibility caused by adding Sc and Zr is from refining grains and restraining the formation of precipitate free zone. The improved corrosion resistance from prolonging aging time at 120°C is due to the coarsening of matrix and grain boundary precipitates, and the increased spacing of grain boundary precipitates. Aged at 120°C for 36. h, the Al-Zn-Mg alloy microalloyed with 0.25. wt.% Sc and 0.10. wt.% Zr exhibits high mechanical properties and admirable corrosion resistance. © 2012 Elsevier Ltd. Source


Shen J.,Northeast Light Alloy Co.
Jinshu Rechuli/Heat Treatment of Metals | Year: 2012

Effect of solution temperature and time on microstructure and properties of 7050 aluminum alloy thick plate were investigated by DSC test, room temperature tensile test, electrical conductivity measurement and microstructure observation. The results show that the overburnt temperature of the alloy is about 486.3 °C. With solution temperature increasing, the electrical conductivity decreases, the ultimate strength first increases and then decreases. When solution temperature is higher than overburnt temperature, the elongation decreases rapidly. After solution treated at 480 °C for 90 min, the ultimate tensile strength, yield strength and elongation of the alloy for T6 condition are 600 MPa, 525 MPa and 15.0%, respectively. The reasonable solution process of the alloy is 480 °C×(90-120) min. Source


Deng Y.,Central South University | Yin Z.,Central South University | Zhao K.,Central South University | Duan J.,Central South University | He Z.,Northeast Light Alloy Co.
Journal of Alloys and Compounds | Year: 2012

Effects of Sc and Zr microalloying additions on the microstructure and mechanical properties of new Al-Zn-Mg alloys alloyed with a small amount of copper were investigated comparatively by tensile tests and microscopy methods. Compared with the strength of peak-aged Al-Zn-Mg alloy, the yield strength increased by 66 MPa after adding 0.10 wt.% Sc and 0.10 wt.% Zr, and improved by 96 MPa after adding 0.25 wt.% Sc and 0.10 wt.% Zr, respectively. Introduction of 0.10 wt.% Zr to Al-Zn-Mg alloy, the grain refinement effect of scandium did not occur by adding only 0.10 wt.% Sc, but appeared with an increase in scandium content to 0.25 wt.%. In the presence of 0.10 wt.% Zr, antirecrystallized effect of scandium appeared at 0.10 wt.% scandium concentration, and enhanced with an increase in the content of scandium. Main aging precipitates were two kinds of GP zones in under-aged alloys, and η′ phases in peak-aged alloys, respectively. Small additions of Sc and Zr did not retard or suppress the formation of aging precipitates in Al-Zn-Mg-Sc-Zr alloys. The strengthening effect from aging precipitates was much stronger than from Sc and Zr microalloying additions in Al-Zn-Mg-Sc-Zr alloys. In addition, the most important strengthening mechanisms of Sc and Zr microalloying in aged Al-Zn-Mg alloys was Orowan strengthening of secondary Al 3(Sc, Zr) particles. © 2012 Elsevier B.V. All rights reserved. Source


Deng Y.,Central South University | Yin Z.,Central South University | Duan J.,Central South University | Zhao K.,Central South University | And 2 more authors.
Journal of Alloys and Compounds | Year: 2012

The microstructural and property evolution of a novel Al-Zn-Mg-Sc-Zr sheet during its preparation were investigated in detail by tensile tests and electron microscopy methods. The results show that severe segregation exists in the ingot. After homogenization treatment at 470 °C for 12 h, dissoluble Zn and Mg enriched non-equilibrium phases dissolve into matrix completely and only little indissoluble impurity phases containing Fe and Si elements remain. At the same time, precipitation of nanometer-scaled coherent secondary Al 3(Sc, Zr) particles from a supersaturated solid solution occurs. The proper homogenization process is 470 °C × 12 h. After solution treatment at 470 °C for 1 h, a lot of non-equilibrium T(Mg 32(Al,Zn) 49) phases formed during hot rolling dissolve into matrix. Aged at 120 °C, the precipitates gradually transform from coherent GP zones to semi-coherent η′ phase and incoherent η phase for the duration of aging, exhibiting a typical behavior of aging strengthening. The optimal solution-aging process is solution treated at 470 °C for 1 h, followed by water quenching and then aged at 120 °C for 24 h (peak-aged). Under this condition, the ultimate tensile strength, yield strength and elongation reach 555 ± 2 MPa, 524 ± 4 MPa and 12.3 ± 0.6% respectively. The main strengthening mechanisms of Al-Zn-Mg-Sc-Zr aged sheets are precipitation strengthening derived from η′ precipitates, and dispersion strengthening and sub-grain strengthening caused by coherent secondary Al 3(Sc, Zr) particles. © 2011 Elsevier B.V. Source


Deng Y.,Central South University | Yin Z.,Central South University | Cong F.,Northeast Light Alloy Co.
Intermetallics | Year: 2012

Intermetallic phase evolution of 7050 aluminum alloy during homogenization was investigated in detail by optical microscopy, scanning electron microscopy, energy dispersive spectrometry, differential scanning calorimetry, electron probe micro-analysis and X-ray diffraction methods. The results show that severe dendritic segregation exists in as-cast alloy. The dissolvable intermetallic phases in as-cast alloy consist of equilibrium η (MgZn 2) phase, Cu and Mg enriched non-equilibrium aluminides and Cu enriched non-equilibrium aluminides. During homogenization, Cu and Mg enriched non-equilibrium aluminides, Cu enriched non-equilibrium aluminides and η (MgZn 2) phase gradually dissolve into matrix. Equilibrium S (Al 2CuMg) intermetallic phase nucleates and grows along the grain boundaries, and it disappears completely after multi-step homogenization. The proper homogenization processing is 400°C × 10 h step470°C × 24 h step485°C × 4 h, which is consistent with the results of homogenizing kinetic analysis. © 2012 Elsevier Ltd. All rights reserved. Source

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