Microstructural evolution of high strength 7B04 ingot during homogenization treatment

The evolution of the microstructure and phases of the direct chill semicontinuous casting ingot of 7B04 super-high strength aluminum alloy during homogenization treatment was studied with metallographic analysis, scanning electron microscopy（SEM）, energy spectroscopy and differential scanning calorimetry（DSC）. The results show that a considerable amount of non-equilibrium eutectics containing AI, Zn, Cu and Mg exist in the direct chill semicontinuous casting ingot of 7B04 super-high strength aluminum alloy, and their melting point is 478℃. During homogenization treatment at 470℃, these eutectics dissolve into the matrix partly, coarsen and also transform into Al2CuMg phase whose equilibrium melting point is 490℃ in the alloy. Moreover, the homogenization treatment at 470℃ for 72 h results in the disappearance of the non-equilibrium eutectics though Al2CuMg phase can not dissolve completely.     

新型Al-Mg-Cu铝合金铸锭均匀化过程中相的变化

采用金相、扫描电镜、能谱和DSC分析方法研究了新型Al-Mg-Cu铝合金(以下简称A铝合金)半连续水冷铸锭均匀化处理过程中相的变化.结果表明,A铝合金半连续铸锭的铸态组织中存在大量非平衡凝固的含Al2CuMg和Al2Cu的共晶相,其熔化温度为505℃;在595℃12 h均匀化过程中,该合金铸锭中非平衡凝固共晶相发生溶解,合金中铸造过程形成的非平衡凝固共晶体Al2Cu全部消失,但Al2CuMg相不能完全溶解.     

Mn元素在7A99铝合金中微观组态分布的研究

通过半连续铸造方式向7A99铝合金中添加0.4%Mn(质量分数)元素,采用SEM、TEM、HRTEM与三维原子探针(3DAP)开展Mn元素在7A99铝合金铸锭、均匀化以及固溶时效过程中的微观组态分布的研究。结果表明,Mn元素在7A99铝合金铸锭中主要以晶界处鱼骨状的含AlZnMgCuMn的MgZn2型非平衡共晶化合物形式存在;均匀化处理后,Mn元素在7A99铝合金中主要以Al₆Mn析出相与断续、细小、颗粒状的含AlZnMgCuMn的S型(Al₂CuMg)第二相形式存在;固溶处理后,Mn元素主要以Al₆Mn析出相形式存在,其尺寸范围处于0.2~1μm;120℃时效过程中,Mn元素始终主要以与尺寸稳定、与铝基体非共格的Al₆Mn析出相形式存在;Mn元素在120℃时效过程中未析出新相,且未参与影响7A99铝合金中Zn、Mg元素的时效析出行为。     

Research on microstructure in as-cast 7A55 aluminum alloy and its evolution during homogenization

The microstructure of the as-cast 7A55 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analysis. The results indicate that the microstructure of the as-cast 7A55 aluminum alloy mainly consists of the dendritic network of aluminum solid solution, Al/AlZnMgCu eutectic phases, and intermetallic compounds MgZn2, Al2CuMg, Al7Cu2Fe, and Al23CuFe4. After homogenization at 470°C for 48 h, Al/AlZnMgCu eutectic phases are dissolved into the matrix, and a small amount of high melting-point secondary phases were formed, which results in an increasing of the starting melting temperature of 7A55 aluminum alloy. The high melting-point secondary phases were eliminated mostly when the homogenization time achieved to 72 h. Therefore, the reasonable homogenization heat treatment process for 7A55 aluminum alloy ingots was chosen as 470°C/72 h.     

Effect of homogenization treatment on microstructure and hot workability of high strength 7B04 aluminium alloy

The effects of homogenization treatment on microstructure, overbumt temperature and hot rolling plasticity of high strength 7B04 aluminium alloy were investigated. Under the condition of homogenization at 470 ℃, the starting melting temperature of the primary eutectics in ingot of non-equilibium solidified 7B04 alloy is 478 ℃. Using two-step homogenization processing at ultra-high temperature which comprises heating the ingots to 470 ℃ at 10 ℃/h and holding for 64 h, and then heating to 500 ℃ at 1 ℃/h and holding for 10 h, the ingots of 7B04 aluminium alloy could safely pass the sensitive overbumt zone between 480 ℃ and 495 ℃, and the ordinary burnt phenomena of the ingots between 480 ℃ and 495 ℃ does not occur because the excess low-melting point eutectic phases in the as-cast alloy dissolve into the matrix during the two-step homogenization processing. Consequently, the hot rolling plasticity of ingot of 7B04 aluminium alloy is greatly improved.     

Microstructural evolution of direct chill cast Al-15.5Si-4Cu-1Mg-1Ni-0.5Cr alloy during solution treatment

Heat treatment has important influence on the microstructure and mechanical properties of Al-Si alloys. The most common used heat treatment method for these alloys is solution treatment followed by age-hardening. This paper investigates the microstructural evolution of a direct chill (DC) cast Al-15.5Si-4Cu-1Mg-1Ni-0.5Cr alloy after solution treated at 500, 510, 520 and 530℃, respectively for different times. The major phases observed in the as-cast alloy are α-aluminum dendrite, primary Si particle, eutectic Si, Al7Cu4Ni, Al5Cu2Mg8Si6, Al15(Cr, Fe, Ni, Cu)4Si2 and Al2Cu. The Al2Cu phase dissolves completely after being solution treated for 2 h at 500℃, while the eutectic Si, Al5Cu2Mg8Si6 and Al15(Cr, Fe, Ni, Cu)4Si2 phases are insoluble. In addition, the Al7Cu4Ni phase is substituted by the Al3CuNi phase. The α-aluminum dendrite network disappears when the solution temperature is increased to 530℃. Incipient melting of the Al2Cu-rich eutectic mixture occurrs at 520℃, and melting of the Al5Cu2Mg8Si6 and Al3CuNi phases is observed at a solution temperature of 530℃. The void formation of the structure and deterioration of the mechanical properties are found in samples solution treated at 530℃.     

Homogenization heat treatment of 2099 Al–Li alloy

The microstructure evolution and composition distribution of as-cast and homogenized 2099 aluminum– lithium(Al–Li) alloy were studied by optical microscopy(OM), differential thermal analysis(DTA), scanning electron microscopy(SEM), energy dispersive spectrometry(EDS), area and line scanning, X-ray diffraction(XRD), and Vickers microhardness test methods. The results show that severe dendrite exists in the as-cast alloy. Cu, Zn, Mn, and Mg distribute unevenly from the grain boundary to inside. The low-melting point nonequilibrium eutectic phases dissolve into the matrix during the first-step homogenization, whereas the melting point of residual eutectic phases is elevated. After the second-step homogenization, most of the remaining eutectic phases dissolve into the matrix, except a small amount of Al–Cu–Fe phases. An optimized homogenization process of the 2099 Al–Li alloy is developed(515 °C 9 18 h ? 525 °C 9 16 h), which shows a good agreement with the homogenization kinetic analysis results.     

大规格铸态7005铝合金的双级均热工艺优化

为优化工业化生产耗时长、耗能高、效率低的旧双级均热工艺,采用OM、SEM、图像分析软件及布氏硬度计,研究了双级均热工艺对大规格铸态7005铝合金圆锭显微组织和硬度的影响。结果表明:经450℃×2h+470℃×32h双级均热处理后,MgZn2弥散质点完全溶解,仅残留难溶的AlMnFe、AlMnFeSi等含Fe化合物相,均热效果与旧工艺的均热效果一致,可实现工业化节能降本提质增效的生态生产。     

Al-4.5Cu-3.5Zn-0.5Mg铸造铝合金的均匀化工艺及组织演变

对Al-4.5Cu-3.5Zn-0.5Mg铸态合金进行不同双级均匀化处理,采用扫描电镜、电子探针显微分析仪、差示扫描量热仪和光学显微镜等,研究了该合金的铸态组织及其在均匀化过程中的组织演变。结果表明:铸态组织主要由α-Al、粗大Al₂Cu相以及少量AlZnMgCu、Al₇Cu₂Fe相组成,合金元素枝晶偏析严重。经470 ℃×12 h均匀化处理后,AlZnMgCu相已基本回溶至基体;第二级均匀化温度由490 ℃逐渐升高到520 ℃或者延长保温时间,Al₂Cu相逐渐回溶至基体,合金元素分布趋于均匀。合金过烧温度为520 ℃,最佳双级均匀化制度为470 ℃×12 h+510 ℃×32 h,该制度与均匀化动力学计算结果基本一致。     

均匀化处理对Al-Cu-Mg合金组织和性能的影响

利用光学显微镜、扫描电镜、能谱分析、差热分析、硬度测试和拉伸测试等方法研究了均匀化处理对Al-4.5Cu-0.8Mg合金的组织和性能的影响。结果表明:Al-4.5Cu-0.8Mg铸态组织中存在较严重的枝晶偏析现象,晶界及晶界交汇处有大量Al2Cu相及Al2Cu和Al2CuMg的共晶相,合金经480℃×12 h均匀化处理后,组织中的非平衡相已基本溶解,综合力学性能较好,抗拉强度为320 MPa,屈服强度为246 MPa,伸长率为10.2%,硬度为139.2 HV。     

超高强7055铝合金铸锭均匀化工艺优化

采用光学显微镜、扫描电镜、差热分析及透射电镜等手段,对一种航空用超高强7055铝合金大尺寸铸锭的均匀化工艺进行分析与优化。提出分级提高均匀化温度的方法,在确保不发生过烧的情况下,最大限度改善铸锭质量。结果显示:低温预均匀化时,铸锭中析出大量的Al₃Zr相,能够大幅度降低对后续挤压变形的再结晶比例;对铸锭采用400 ℃×4 h+465 ℃×16 h+474 ℃×8 h的分级均匀化处理工艺,能够显著消除铸锭中低熔点相的含量,提高铸锭质量,同时相比于原工艺节省约13 h。新的均匀化处理工艺,不仅提高了生产效率,还能够为后续工艺提供良好的铸锭。     

Phases and microstructures of high Zn-containing Al–Zn–Mg–Cu alloys

Phases and microstructures of three high Zncontaining Al–Zn–Mg–Cu alloys were investigated by means of thermodynamic calculation method, optica microscopy(OM), scanning electron microscopy(SEM)energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), and differential scanning calorimetry(DSC) analysis. The results indicate that similar dendritic network morphologies are found in these three Al–Zn–Mg–Cu alloys. The as-cast 7056 aluminum alloy consists of aluminum solid solution, coarse Al/Mg(Cu, Zn, Al)_2 eutectic phases, and fine intermetallic compounds g(MgZn_2). Both of as-cast 7095 and 7136 aluminum alloys involve a(Al)eutectic Al/Mg(Cu, Zn, Al)_2, intermetallic g(MgZn_2), and h(Al_2Cu). During homogenization at 450 °C, fine g(MgZn_2) can dissolve into matrix absolutely. After homogenization at 450 °C for 24 h, Mg(Cu, Zn, Al)_2 phase in 7136 alloy transforms into S(Al_2Cu Mg) while no change is found in 7056 and 7095 alloys. The thermodynamic calculation can be used to predict the phases in high Zncontaining Al–Zn–Mg–Cu alloys.     

均匀化处理对含钪Al-Zn-Mg-Zr合金组织的影响

采用金相分析、扫描电镜、能谱分析、DSC等手段研究含钪Al-Zn-Mg-Zr合金均匀化态显微组织的演变。结果表明：在合金铸态组织中存在大量的枝晶偏析,在晶界处存在很多低熔点共晶相,主要元素在枝晶内部区域呈周期性变化;合金中元素Zn、Mg和Cu在晶内及晶界分布不均匀;在均匀化过程中,随着均匀化温度的升高或时间的延长,残留相逐渐溶入基体,元素分布逐渐均匀。合金的过烧温度为476.7°C。当均匀化温度升高到480°C时,合金中开始出现复熔球和三角晶界。综合考虑：合金的最佳均匀化制度为470°C,24 h。     

Microstructures of super high strength Al–10Zn–2˙5Mg–2˙3Cu–0˙14Zr alloys under electromagnetically stirred direct chill casting

Abstract

In this report solidification and homogenisation structures of a super high strength aluminium Al–Zn–Mg–Cu alloy were discussed. Al–9˙8Zn–2˙5Mg–2˙3Cu–0˙14Zr alloy was produced by low frequency electromagnetic casting. Solidification structure constituents of this alloy cast by low frequency electromagnetic casting was first discussed, in particular, boundary phases formed mostly by eutectic reaction were discussed: MgZn₂ included with Cu is a major eutectic phase in boundaries; T [Mg₃₂(Al,Zn)₄₉] included with Cu and Si, and S (Al₂CuMg) are located with boundaries as eutectics; Al₂Cu is crystallised as eutectic among which a part is found separately as globular; Al₇Cu₂Fe is crystallised as a facet shape. Second microstructure homogenised for 10 h at 460^u C was discussed. Constituents homogenised were MgZn₂ with Cu and Al₇Cu₂Fe with Zn.     

固溶处理对7B04铝合金冷轧板组织性能的影响

在实验室中制备了试验用7B04铝合金,经铸造-均质化退火-热轧-中间退火-冷轧后制得7B04铝合金板材,并对合金板材进行了后续固溶时效处理,研究了固溶处理对其组织和性能的影响。结果表明,470 ℃×1 h固溶+120 ℃×21 h时效处理铝合金冷轧板材再结晶明显,有少量晶粒处于伸长状态,除粗大第二相粒子外,未发现细小第二相粒子,综合力学性能较好,抗拉强度为596 MPa,屈服强度为537 MPa,伸长率为14.88%。固溶温度达到480 ℃时,合金再结晶明显,但保温时间不能超过0.5 h,否则合金强度和塑性下降。     

Al-Cu-Li-Mn-Zr-Ti合金在均匀化过程中的组织演变

采用光学显微镜(OM)、扫描电镜(SEM)、能谱分析(EDX)和差示扫描热分析法(DSC)研究 Al?Cu?Li?Mn?Zr?Ti 合金在均匀化过程中的组织转变。结果表明,实验合金的铸态组织中存在严重的枝晶偏析,晶界处存在大量的共晶相,主要合金元素沿枝晶区域呈周期性分布。合金中的主要未溶相为Al2Cu相,过烧温度为520°C;均匀化过程中,随着温度的升高和时间的延长,晶界处的第二相逐渐溶入基体中,晶界逐渐变得稀疏;合金的均匀化过程可以用一指数方程描述;实验合金适宜的均匀化制度为(510°C,18 h),这与采用均匀化动力学方程计算的结果基本吻合。     

Al-6.3Zn-2.8Mg-1.8Cu铸造铝合金的组织和室温力学性能

研究了Al-6.3Zn 2.8Mg-1.8Cu铸造铝合金的组织和室温力学性能.研究表明,在金属型铸造条件下,Al-6.3Zn-2.8Mg-1.8Cu合金的铸态组织为近等轴晶,相组成为α（Al）基体、枝晶间α（Al）+η（MgZn₂）共晶、晶内游离η相（MgZn₂）、少量T相（Mg₃Zn_xCu₃-_xAl₂）及少量颗粒状Al₇Cu₂Fe.固溶处理后,原铸态组织中的η（MgZn₂）相大部分溶解消失,但形成新的沿晶界分布的S相（Al₂CuMg）.实验确定了固溶态Al-6.3Zn-2.8Mg-1.8Cu合金较优的单级和双级时效工艺.与单级时效工艺相比,采用双级时效工艺处理后,抗拉强度由480 MPa增加至490 MPa,延伸率由0.2%增加至2.2%.     

分级均匀化对7055铝合金组织和力学性能的影响

采用差热分析、X射线衍射分析、光学显微镜、扫描电镜、透射电镜和常温拉伸等方法研究分级均匀化工艺对7055铝合金显微组织、枝晶偏析、Al3Zr粒子析出行为和力学性能的影响。结果表明:合金经(468℃、24h)+(473℃、4 h)的分级均匀化处理后,消除了铸锭晶界上的非平衡凝固共晶组织;铸锭先于264℃保温最有利于获得尺寸细小、均匀弥散分布的Al3Zr粒子;在单级均匀化基础上增加473℃的短时高温均匀化,能够提高合金基体中溶质原子的固溶度,增强时效强化效果,提高综合性能。     

Effects of Solution Treatment on the Microstructure and Mechanical Properties of Al-16.9Si-4.5Cu-0.15Mg Alloy

In this paper, the microstructure and mechanical properties of Al-Si-Cu-Mg casting alloy under different solution conditions were investigated by optical metallographic and mechanical property test. The results show that the cast alloys were composed of α-Al, primary Si, eutectic Si, Al2Cu and Al7Cu2Fe phases. Three changes took place during solution treatment: Firstly, with the increase of solution temperature and the solution holding time extension, more and more Al2Cu phase was dissolved into the matrix; Secondly, with the increase of solution temperature and the solution holding time extension, morphology of eutectic Si, Al7Cu2Fe and other insoluble phases changed into more round; Thirdly, at the fixed solution temperature, if the solution time extended too long, it would cause grains, eutectic Si and other insoluble phases aggregated and coarsened. About mechanical properties, when the solution time was fixed, the hardness, tensile strength and the yield strength of the Al-Si-Cu-Mg alloy treated by T6 enhanced while the solution temperature increasing, and when the solution temperature was fixed, the ultimate tensile strength and the elongation of the Al-Si-Cu-Mg alloy treated by T6 increased at first and then decreased while the solution time increasing, but the hardness of the alloys affected less by the solution time.     

Macrosegregation of ternary Al–4·5wt-%Cu–1·0wt-%Mg alloy in horizontal direct chill casting: implementation of non-equilibrium microsegregation model

Abstract

An extended and modified continuum mixture model for macrosegregation in solidifying alloys is applied to the case of horizontal direct chill casting (HDC) of a ternary Al–4·5Cu–1·0Mg (wt-%) alloy. A thermodynamic closure model for a Al–Cu–Mg alloy is coupled with an extended mixture continuum model to obtain steady state macrosegregation fields for the different casting parameters (e.g. casting speed, inlet superheat and inlet plenum position) in this study. Macrosegregation calculations were performed assuming that the solid forms a rigid and stationary network in all parts of the mushy zone. A microsegregation non-equilibrium model is used to calculate phase fraction compositions and phase distributions. The Cu exhibits more segregation compared to the previous study of a binary Al–Cu alloy, while Mg has a similar segregation profile in all cases but less pronounced. The phase compositions show that Cu is mostly distributed in secondary and ternary phases, while Mg is uniformly configured in the primary (Al) and ternary phase (Al₂CuMg). The primary Al phase is dominant (over 90%) in all cases, with highest peaks in depleted regions below the centreline of slab, except in the case where the inlet plenum is positioned on the bottom of the refractory plate due to a different flow pattern.