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Lu X.-Y.,Harbin University of Science and Technology | Lu X.-Y.,Northeast Light Alloy Co. | Guo E.-J.,Harbin University of Science and Technology | Rometsch P.,Monash University | Wang L.-J.,Northeast Light Alloy Co.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2012

Semi-quantitative electron probe microanalysis (EPMA) mapping, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to study the effect of one-step and two-step treatments on the Zr distribution and Al3Zr dispersoid characteristics in as-cast commercial AA7150 aluminum alloy. It is shown that the Zr concentration in the dendrite centre regions is higher than that near the dendrite edges in the as-cast condition, and that homogenization at 460°C for 20 h is insufficient to remove these concentration gradients. After homogenizing at 460-480°C, a high number density of larger dispersoids can be observed in dendrite centre regions but not near dendrite edges. Furthermore, the dispersoid size increases with increasing the temperature during both one-step and two-step homogenization treatments. © 2012 The Nonferrous Metals Society of China.


He Z.-B.,Central South University | He Z.-B.,Northeast Light Alloy Co. | Peng Y.-Y.,University of South China | Yin Z.-M.,Central South University | Lei X.-F.,Central South University
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2011

In order to study the welding process, microstructure and properties of Al-Mg-Mn-Sc-Zr alloy, comparative methods of friction stir welding (FSW) and tungsten inert gas (TIG) were applied to the two conditions of this alloy, namely hot rolled plate and cold rolled-annealed plate. The relationships between microstructures and properties of the welded joints were investigated by means of optical microscopy and transmission electron microscopy. Compared with the base metal, the strength of FSW and TIG welded joints decreased, and the FSW welding coefficients were higher than the TIG welding coefficients. The loss of substructure strengthening and a very little loss of precipitation strengthening of Al 3(Sc, Zr) cause the decreased strength of FSW welded joint. But for the TIG welded joint, the disappearance of both the strain hardening and most precipitation strengthening effect of Al 3(Sc, Zr) particles contributed to its softening. At the same time, the grains in weld nugget zone of FSW welded joints were finer than those in the molten zone of TIG welded joints. © 2011 The Nonferrous Metals Society of China.


Xu C.,Harbin Institute of Technology | Xu C.,Nagaoka University of Technology | Xu S.W.,Nagaoka University of Technology | Zheng M.Y.,Harbin Institute of Technology | And 5 more authors.
Journal of Alloys and Compounds | Year: 2012

Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy sheets containing long period stacking ordered (LPSO) phase were prepared by hot rolling at 400 °C with total reduction of 96%. Microstructure evolution of the sheets during hot rolling was investigated, and its influence on mechanical properties was discussed. Twinning occurred during the early stage of hot rolling, and disappeared after total reduction higher than 89%. Average grain size was gradually refined, microstructure became much more homogeneous and volume fraction of LPSO phase decreased with increasing rolling reduction. Furthermore, the type of LPSO phases far from and near the block shaped phases were identified to be different. Basal texture was obtained during rolling process, but the intensity declined with the further rolling, which is mainly due to the dynamic recrystallization and the addition of RE elements. The as-rolled sheet with 96% reduction shows excellent mechanical properties: yield strength of 318 MPa, ultimate tensile strength of 403 MPa and elongation to failure of 13.7% at ambient temperature along the rolling direction. © 2012 Elsevier B.V.


Miao Q.,Harbin Institute of Technology | Hu L.,Harbin Institute of Technology | Wang G.,Northeast Light Alloy Co. | Wang E.,Harbin Institute of Technology
Materials Science and Engineering A | Year: 2011

AZ31 magnesium alloy sheets were produced by conventional rolling at a temperature range of 433-523. K and subsequent annealing. The process could be optimized to produce sheets with grains as fine as 2.8 μm in average size. Obvious dynamic recrystallization was found to occur during rolling at temperature above 473. K. For the sheets rolled at temperature below 473. K, a subsequent annealing was needed to obtain a fine fully recrystallized microstructure, which gives rise to a significant increase in ductility as compared with the as-rolled state. The sheets produced by the processing route in the present study exhibit excellent mechanical properties, with the yield strength and tensile elongation achieving as high as 350. MPa and 35%, respectively. Their mechanical properties and the Hall-Petch relationship were compared with those magnesium alloys processed by other deformation methods. The results show that the present process offers a cost-effective way to produce high-performance Mg alloy thin sheets. © 2011 Elsevier B.V.


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.


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.


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.


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.


Liu X.D.,Northeast Light Alloy Co. | Wang G.J.,Northeast Light Alloy Co. | Lv X.Y.,Northeast Light Alloy Co.
Materials Science and Engineering A | Year: 2013

A large Mg-4.50Zn-1.13Ca (wt%) alloy ingot 350mm in diameter and 1730mm long was successfully fabricated by semi-continuous casting. The microstructures and mechanical properties of the as-cast and as-extruded alloys were investigated. The as-cast alloy exhibits uniform chemical composition and microstructure from the centre to the surface of the ingot and mainly consists of α-Mg and Ca2Mg6Zn3. The coarse grains and network-like second phases that are distributed at the grain boundaries result in poor mechanical properties for the as-cast alloy. The mechanical properties of the as-extruded alloys are significantly enhanced. The high yield strengths of the as-extruded alloys mainly result from the fine DRXed grain and the stronger basal texture. © 2013 Elsevier B.V.


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.

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