Microstructure of Al-Zn-Mg-Cu-Zr-0.5Er alloy under as-cast and homogenization conditions

The billets of Al-Zn-Mg-Cu-Zr and Al-Zn-Mg-Cu-Zr-0.5Er alloys were prepared by semi-continuous direct chill casting （DCC）.The effects of trace Er on microstructure of Al-Zn-Mg-Cu-Zr alloy under as-cast and homogenization conditions were studied.The results show that the grain morphology is large dendritic structure and the grain size increases obviously by the addition of 0.5% Er.Moreover,most of Er element in the alloy segregates at grain boundary during solidification,resulting in ternary Al8Cu4Er phase.After homogenization,most of the MgZn2 phase at grain boundary has dissolved back to Al matrix in the two alloys.In the Er-containing alloy,the dissolution temperature of Al8Cu4Er phase is about 575 °C.Therefore,the homogenization treatment cannot eliminate Al8Cu4Er phase validity.

Effect of homogenization treatment on microstructure and mechanical properties of DC cast 7X50 aluminum alloy

The evolution of the eutectic structures in the as-cast and homogenized 7X50 aluminum alloys was studied by scanning electron microscopy(SEM), transmission electron microscopy(TEM), energy dispersive spectrometer(EDS), differential scanning calorimetry(DSC), X-ray diffraction(XRD) and tensile test. The results show that the main phases are S(Al2CuMg), T(Al2Mg3Zn3) and Mg Zn2, with a small amount of Al7Cu2 Fe and Al3 Zr in the as-cast 7X50 alloy. The volume fraction of the dendritic-network structure and residual phase decreases gradually during the homogenization. After homogenization at 470 °C for 24 h and then 482 °C for 12 h, the T(Al2Mg3Zn3) phase disappears and minimal S(Al2CuMg) phase remains, while almost no change has happened for Al7Cu2 Fe. There is a strong endothermic peak at 477.8 °C in the DSC curve of as-cast alloy. A new endothermic peak appears at 487.5 °C for the sample homogenized at 470 °C for 1 h. However, this endothermic peak disappears after being homogenized at 482 °C for 24 h. The T(Al2Mg3Zn3) phase cannot be observed by XRD, which is consistent with that T phase is the associated one of S(Al2CuMg) phase and Mg Zn2 phase. The volume fraction of recrystallized grains is substantially less in the plate with pre-homogenization treatment. The strength and fracture toughness of the plate with pre-homogenization treatment are about 15 MPa and 3.3 MPa·m1/2 higher than those of the material with conventional homogenization treatment.

Microstructural evolution of new type Al-Zn-Mg-Cu alloy with Er and Zr additions during homogenization

A comprehensive study on the microstructural evolution of a new type Al-Zn-Mg-Cu-Er-Zr alloy duringhomogenization was conducted by optical microscope,scanning electron microscope,transmission electron microscopy and X-raydiffraction analysis.The results show that serious segregation exists in as-cast alloy,and the primary phases are T(AlZnMgCu),S(Al2CuMg)and Al8Cu4Er,which preferentially locate in the grain boundary regions.The soluble T(AlZnMgCu)and S(Al2CuMg)phases dissolve into the matrix gradually during single-stage homogenized at465°C with prolonging holding time,but the residualAl8Cu4Er phase cannot dissolve completely.Compared with the single-stage homogenization,both a finer particle size and a highervolume fraction of L12-structured Al3(Er,Zr)dispersoids can be obtained in the two-stage homogenization process.A suitablehomogenization scheme for the present alloy is(400°C,10h)+(465°C,24h),which is consistent with the results of homogenizationkinetic analysis.

Effect of Y Addition on Microstructure and Constituent Phases of Al-Ti-C Master Alloy

Al-Ti-C master alloy was prepared by SHS (Self-propagating High temperature Synthesis)-melting technique. Effect of yttrium addition level on the microstructures of the master alloy was studied by XRD, SEM and EDS. The experimental results show that the addition of 1.0% Y is beneficial to the formation of TiC particles; Al-Ti-C-1.0Y consists of rod-like and blocky TiAl3, TiC, Al3Y and α-Al matrix. Y is found around TiC particles in Al-Ti-C-0.5Y master alloy while blocky (AlTiY) phase appears in Al-Ti-C-1.0Y master alloy. Al3Y with dendritic morphology and small blocky Al2Y except for TiC are found in Al-Ti-C-2-0Y master alloy.

MICROSTRUCTURE STUDY OF CONSTITUENT PHASES IN 2024 SERIES Al ALLOYS

X-ray microanalysis,convergent beam electron diffraction(CBD)and selected area electron diffraction(SAD)studies on the structures and compositions of the constituent phases in 2024 series Al alloys have been conducted.Partial substitution of alloying elements is found to occur in all the constituent phases,which cause small deviations from the stoichiometric com- positions reported in these ternary compounds.The dominant phase is α-Al_(12)(FeMn)_3Si which has a body center cubic crystal structure with the Im■ space group and a=1.25 nm.The next dominant phase is Cu_2FeAl_7 which has a primitive tetragonal crystal structure with the P4/mnc space group and a=0.6336 nm,c=1.487 nm.The minor phase is α'-Al_(12)Fe_3Si hav- ing α primitive cubic crystal structure with the Pm■ space group and α=1.27 nm.

Intermetallic phase evolution of 5059 aluminum alloy during homogenization

Intermetallic phase evolution of 5059 aluminum alloy during homogenization was investigated by means of optical microscopy （OM）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, energy dispersive spectrometry （EDS）, differential scanning calorimetry （DSC） and X-ray diffraction analysis （XRD）. The results show that severe dendritic segregation exists in as-cast alloy. The dissolvable intermetallic phases in as-cast alloy consist of Zn-and Cu-rich non-equilibriumβ（Al3Mg2） phase, Fe-rich eutectic Al6Mn phase and equilibrium Mg2Si phase. During the homogenization, Zn- and Cu-rich non-equilibrium β （Al3Mg2） phase, Fe-rich eutectic Al6Mn phase and equilibrium Mg2Si gradually dissolve into matrix. Fine dispersed β（Al3Mg2） particles and rod-shaped Al6Mn particles form in the Al matrix after homogenization. The proper homogenization processing is at 450 °C for 24 h, which is consistent with the results of homogenizing kinetic analysis.

Microstructural evolution of Al-Zn-Mg-Zr alloy with trace amount of Sc during homogenization treatment

The microstructural evolution of Al-Zn-Mg-Zr alloy with trace amount of Sc during homogenization treatment was studied by means of metallographic analysis, scanning electron microscopy （SEM）, energy dispersive X-ray （EDX） and differential scanning calorimetry （DSC）. The results show that serious dendritic segregation exists in studied alloy ingot. There are many eutectic phases with low melting-point at grain boundary and the distribution of main elements along interdendritic region varies periodically. Elements Zn, Mg and Cu distribute unevenly from grain boundary to the inside of alloy. With increasing the homogenization temperature or prolonging the holding time, the residual phases are dissolved into matrix α（Al） gradually during homogenization treatment, all elements become more homogenized. The overburnt temperature of studied alloy is 476.7 °C. When homogenization temperature increases to 480 °C, some spherical phases and redissolved triangular constituents at grain boundaries can be easily observed. Combined with microstructural evolution and differential scanning calorimeter, the optimum homogenization parameter is at 470 °C for 24 h.

Microstructure and corrosion behavior of as-homogenized and as-extruded Mg-xLi-3Al-2Zn-0.5Y alloys(x=4,8,12)

The microstructure and corrosion behavior of the as-homogenized and as-extruded Mg-xLi-3Al-2Zn-0.5Y alloys(x=4,8,12,wt.%)were studied.The results show that as the Li content increases from 4%to 12%,the matrix transfers from singleα-Mg phase,(α-Mg+β-Li)dual phase to singleβ-Li phase.A mixed corrosion feature of intergranular corrosion and pitting corrosion occurs in the Mg-4Li-3Al-2Zn-0.5Y and Mg-12Li-3Al-2Zn-0.5Y alloys.The former is related to the precipitated AlLi phase along the grain boundaries,and the latter is related to the high potential difference between the second phase and the matrix.The corrosion resistance of the as-extruded alloys is better than that of the as-homogenized alloys.The superior corrosion resistance of the as-extruded Mg-8Li-3Al-2Zn-0.5Y alloy with the lowest corrosion rate(P_(W)=(0.63±0.26)mm/a)is attributed to the more uniform distribution of second phases,the protectiveα-Mg phase via sacrificing theβ-Li phase and the relatively integrated oxide film.

Microstructural evolution during homogenization of DC cast 7085 aluminum alloy

The microstructural evolution of a DC cast 7085 alloy during homogenization treatment was investigated by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry (EDS), differential scanning calorimeter (DSC) and X-ray diffraction (XRD). The results showed that serious dendritic segregation existed in the as-cast 7085 alloy. Numerous eutectic microstructures and phases were observed at the grain boundary. During homogenization process, eutecticα(Al)+T(AlZnMgCu) microstructure gradually was dissolved into matrix. IntermetallicS(Al2CuMg) phase formed and grew along the eutectic microstructure and disappeared into the matrix completely when it was homogenized at 460 °C for 24 h. It could be found that the evolution of primary eutectic structure of 7085 alloy consisted of three processes, dissolution of eutecticα+T microstructure, phase transformation fromT phase toS phase and the dissolution ofS phase. The optimum homogenization parameter was at 470 °C for 24 h.

Influence of Mo content on microstructure and mechanical properties of β-containing TiAl alloy

The influence of Mo content on the microstructure and mechanical properties of the Ti?45Al?5Nb?xMo?0.3Y(x=0.6,0.8,1.0,1.2)alloys was studied using small ingots produced by non-consumable electrode argon arc melting.The results show that smallquantities ofβphase are distributed alongγ/α2lamellar colony boundaries as discontinuous network in the TiAl alloys owing to thesegregation of Mo element.Theγphase forms in the interdentritic microsegregation area when the Mo addition exceeds0.8%.Theβandγphases can be eliminated effectively by subsequent homogenization heat treatment at the temperature above Tα.The evolutionof the strength,microhardness and ductility at different Mo contents under as-cast and as-homogenization treated conditions wasanalyzed,indicating that excessive Mo addition is prone to cause the microsegregation,thus decreasing the strength andmicrohardness obviously,which can be improved effectively by subsequent homogenization heat treatment.

Effect of homogenization process on the hardness of Zn-Al-Cu alloys

The effect of a homogenizing treatment on the hardness of as-cast Zn–Al–Cu alloys was investigated. Eight alloy compositions were prepared and homogenized at 350 °C for 180 h, and their Rockwell 'B' hardness was subsequently measured. All the specimens were analyzed by X-ray diffraction and metallographically prepared for observation by optical microscopy and scanning electron microscopy. The results of the present work indicated that the hardness of both alloys(as-cast and homogenized) increased with increasing Al and Cu contents; this increased hardness is likely related to the presence of the θ and τ′ phases. A regression equation was obtained to determine the hardness of the homogenized alloys as a function of their chemical composition and processing parameters, such as homogenization time and temperature, used in their preparation.

Microstructural evolution of Al-8.59Zn-2.00Mg-2.44Cu during homogenization

The microstructural evolution and phase transformations of a high-alloyed Al-Zn-Mg-Cu alloy （Al-8.59Zn-2.00Mg-2.44Cu,wt%） during homogenization were investigated. The results show that the as-cast microstructure mainly contains dendritic α（Al）, non-equilibrium eutectics （α（Al） ＋ Mg（Zn,Al,Cu）2）, and the θ （Al2Cu） phase. Neither the T （Al2Mg3Zn3） phase nor the S （Al2CuMg） phase was found in the as-cast alloy. The calculated phase components according to the Scheil model are in agreement with experimental results. During homogenization at 460℃, all of the θ phase and most of the Mg（Zn,Al,Cu）2 phase were dissolved, whereas a portion of the Mg（Zn,Al,Cu）2 phase was transformed into the S phase. The type and amount of residual phases remaining after homogenization at 460℃ for 168 h and by a two-step homogenization process conducted at 460℃ for 24 h and 475℃ for 24 h （460℃/24 h ＋ 475℃/24 h） are in good accord with the calculated phase diagrams. It is concluded that the Al-8.59Zn-2.00Mg-2.44Cu alloy can be homogenized adequately under the 460℃/24 h ＋ 475℃/24 h treatment.

Interaction between γ'precipitate distribution and microstructure homogeneity during hot deformation in a Ni-based superalloy

The inhomogeneous microstructure of the Ni-based superalloys used for turbine disks was an intolerable defect for the mechanical performance.The effects of the distribution ofγ'precipitate,forging temperature,and strain level on the microstructure evolution of GH4730 alloy were investigated by EBSD during hot deformation.The results showed that the heterogeneous factor peaked at the transition temperature from the single-phase to the double-phase region.The coupling effect of heat and stress led to the heterogeneous precipitation and distribution ofγ'phase during the transition region,which was the main reason for the formation of inhomogeneous microstructures.The coherentγ'phases of approximately 0.3μm were diffusely distributed inside the large grains,increasing the grain strength,making recrystallization refinement difficult,and thus forming large unrecrystallized grains.The incoherentγ'phases with a size of approximately 1.1μm located at the grain boundaries and pinned the grain boundaries,and thus the accumulated strain at the grain boundaries caused the occurrence of discontinuous dynamic recrystallization and promoted continuous refinement of the grains.The microstructure evolution of new Ni-based superalloys during hot forging was focused,and the formation mechanism of inhomogeneous microstructure and control measures was explained.A theoretical basis for improving the microstructure homogeneity of the new cast and wrought superalloys was provided.

Transformation and dissolution of second phases during solution treatment of an Al-Zn-Mg-Cu alloy containing high zinc

The transformation and dissolution of Mg（Zn, Cu, Al）2 phase during solution treatment of an Al-Zn-Mg-Cu alloy containing high zinc were investigated by means of optical microscopy （OM）, scanning electron microscopy （SEM）, energy-dispersive X-ray spectrometry （EDX） and X-ray diffraction （XRD）. The results show that solution temperature is the main factor influencing phase dissolution. With solution temperature increasing, the content of residual phases decreases. Phase transformation from Mg（Zn, Cu, Al）2 to S（Al2CuMg） occurs under solution temperature of 450, 460 and 465 ℃. Mg（Zn, Cu, Al）2 phase is directly dissolved into the matrix under solution temperature of 470 and 475 ℃, and no S（Al2CuMg） phase transformed from Mg（Zn, Cu, Al）2 phase is observed. The formation of S（Al2CuMg） phase is mainly controlled by Zn elemental diffusion. The mechanism of transformation and dissolution of second phases was investigated. At low temperature, the dissolution of Zn is faster than that of Mg and Cu, resulting in an appropriate condition to form S（Al2CuMg） phase. At high temperature, the dissolution of main alloying elements has no significant barrier among them to form S（Al2CuMg） phase.

Microstructure and mechanical properties of 600 MPa grade ultra-high strength aluminum alloy fabricated by wire-arc additive manufacturing

The utilization of wire-arc additive manufacturing(WAAM)technology for the preparation of Al-Zn-Mg-Cu aluminum alloy has made some progress in recent years.However,the challenge still remains to achieve ultra-high strength(600 MPa)in WAAM.In this study,the crack-free Al-Zn-Mg-Cu-Sc thin-wall component with ultra-high strength was successfully fabricated by the cold metal transfer(CMT)pro-cess using a self-prepared 7B55-Sc filler wire.The microstructures of both as-deposited and T6 heat-treated samples were all composed of fine equiaxed grains with an average size of about 6.0μm.The primary Al_(3)(Sc,Zr)particles acted as heterogeneous nuclei to promote the formation of equiaxed grains and refine the microstructures during the solidification process.A large amount of continuous eutectic structures rich in Al,Zn,Mg,and Cu elements formed along the grain boundaries under the as-deposited condition,and the precipitated second phases within the grains mainly included the equilibriumηphase,metastableηphase and large-sized T phase.After T6 heat treatment,the majority of the second phases originally distributed within grains and along grain boundaries were dissolved into the Al matrix,and a large amount of fine GP zones,ηphase and secondary Al_(3)(Sc,Zr)particles were precipitated within the grains during the aging process.The tensile strength reached a recorded level of 618 MPa in the hori-zontal direction after T6 heat treatment,which was considered a breakthrough for the manufacturing of 600 MPa grade aluminum alloy by WAAM.

均匀化对Al-Zn-Mg-Cu合金第二相与晶粒尺寸的影响

采用光学显微镜(OM)、扫描电镜(SEM)、差示扫描量热仪(DSC)表征,研究了均匀化过程中Al-Zn-Mg-Cu合金的微观组织演变。结果表明,铸态合金晶界中存在大量难溶相Al7Cu2Fe及非平衡共晶相Mg(Zn,Cu,Al)2、Al2CuMg相,在经过420℃/8 h的单级均匀化处理后,部分难溶相和非平衡共晶相回溶到基体中,但还存在大量枝晶偏析,继续进行470℃/36 h第二级均匀化后,非平衡共晶组织和枝晶偏析完全消除。合金的平均晶粒尺寸在两个阶段的均匀化中呈现随时间延长而增加的趋势,基体中残留相及共晶组织的面积分数随保温时长增加而减小,第二级均匀化达到36 h时,相面积分数仅为0.34%,表明均匀化已经非常充分。经过均匀化动力学分析,得出在第二级均匀化温度为470℃时,第二相充分回溶所需保温时间约为37 h,与均匀化的实验结果吻合。

均匀化对Mg-6Zn-0.25Ca镁合金耐蚀性能的影响

本文研究了均匀化对Mg-6Zn-0.25Ca合金耐腐蚀性能的影响。通过XRD、OM、SEM、失重、析氢实验研究了均匀化对Mg-6Zn-0.25Ca合金的显微组织及耐腐蚀性能。实验研究表明铸态Mg-6Zn-0.25Ca合金由α-Mg相以及第二相Ca2Mg6Zn3、Mg2Ca组成,均匀化处理后Mg-6Zn-0.25Ca合金晶粒尺寸稍有变大但是晶粒更加均匀,合金是由α-Mg相以及第二相Mg2Ca组成,由于Ca2Mg6Zn3相的熔点小于均匀化的温度,所以Ca2Mg6Zn3相溶于基体中,Ca2Mg6Zn3相溶于基体导致了合金第二相体积分数减少,第二相体积分数减少有效的降低了电偶腐蚀的发生。析氢失重实验表明进行均匀化处理有效地降低了Mg-6Zn-0.25Ca合金在3.5%NaCl水溶液24小时氢气的产生量,降低了析氢失重速率,即增强了Mg-6Zn-0.25Ca合金的耐腐蚀性能。对腐蚀产物膜进行分析,结果发现经过均匀化处理的合金生成的腐蚀产物膜更加致密,可以有效的增强合金的耐腐蚀性能。

添加第三组元调控Al-Bi偏晶合金凝固组织研究进展

Al-Bi偏晶合金熔体冷却过程中由均一的液相经液-液相转变为两互不混溶的液相,在常规重力铸造条件下极易形成宏观偏析严重的凝固组织,极大限制其工业应用,因此有必要对Al-Bi偏晶合金凝固组织进行有效调控(细化和均匀化)。近年来,研究者对如何改善Al-Bi等偏晶合金偏析组织开展了大量研究,如快速凝固、施加外场和添加第三组元等,其中添加第三组元最有可能实现其低成本/规模化制备。基于此,本文主要综述了Al-Bi偏晶合金添加第三组元(合金元素、Al-(Ti)-(B)体系、陶瓷颗粒)的相关研究进展,其中添加含陶瓷颗粒的第三组元能够有效细化和均匀化富Bi相,获得弥散型Al-Bi基偏晶合金,该研究对于实现其大规模工业应用具有重大意义。

均匀化处理对高Zn超高强铝合金微观组织演变的影响

采用金相光学显微镜、扫描电子显微镜(SEM)等,检测分析了高Zn超高强度铝合金铸锭均匀化前后的组织形貌及变化。结果表明,合金铸态中存在严重的枝晶偏析,合金中的相主要是由MgZn_(2)相和T(AlZnMgCu)相组成的可溶金属间化合物,以及由Mn、Fe和Ni三种元素形成的难溶金属间化合物。铸锭均匀化热处理后的结果显示,与7050合金和7055合金等Zn含量较低的铝合金不同,在合金中Zn含量高达9.8%的情况下没有出现T相向S(Al_(2)CuMg)相的转化。分析表明,这一现象与Zn含量及Zn的扩散密切相关,目前知道Zn含量越高,转化过程越困难。

Al-9.1Zn-1.9Mg-1.6Cu合金均匀化工艺研究

采用光学显微镜、扫描电镜、能谱分析、X射线衍射分析和差示扫描量热分析研究了Al-9.1Zn-1.9Mg-1.6Cu合金铸态与均匀化态显微组织及相组成演化规律。试验结果表明,该合金铸态组织中存在大量的非平衡低熔点共晶相,其初始熔化温度为475℃;合金铸态组织相组成包括α-Al、η-MgZn2及少量的Al7Cu2Fe相;在460℃以上均匀化后,该合金处于α-Al单相区,组织中非平衡低熔点共晶相均能固溶于基体内;465℃×24h是该合金适宜的均匀化处理工艺。