Effects of cooling rate and initial composition on the solidification path and microstructure of Al-Cu-Si alloys

The influences of cooling rate and initial composition on solidification path, microstructure and hardness of Al-Cu-Si alloys were investigated. The results indicate that the solidification paths of alloys Al-3.7Cu-6.5Si, Al-5.2Cu-2.6Si and Al-15.1Cu-6.2Si were (L + α-Al)→(L + α-Al+ β-Si)→(L + α-Al+ β-Si+ θ-Al₂Cu), and the solidification paths of alloys Al-4.6Cu-0.9Si, Al-24.2Cu-3.9Si and Al-26.9Cu-2.1Si were (L + α-Al)→(L + α-Al+ θ-Al₂Cu)→(L + α-Al+ β-Si+ θ-Al₂Cu). Furthermore, it is found that the further the initial compositions from the binary eutectic trough and the slower the cooling rate was, the second dendrite arm spacing was larger and the volume percent of phase θ-Al₂Cu was fewer, and then influence the hardness. There were three kinds of (α-Al+ θ-Al₂Cu) binary eutectic, two kinds of (α-Al+ β-Si+ θ-Al₂Cu) ternary eutectic and one kind of (α-Al+ β-Si) binary eutectic morphologies existed in the solidification specimens.     

Zn/Mg对Al-Zn-Mg合金时效析出惯序的影响

制备了Al6.2Zn2.3Mg和Al5.0Zn3.0Mg两种合金并进行了固溶时效处理,基于EET理论,计算了合金基体固溶体的价电子结构,研究了Zn/Mg对合金时效析出行为的影响。研究认为：Al6.2Zn2.3Mg合金固溶时优先形成的a-Al-Zn-Mg固溶体为η相析出序列GP区的形成提供了条件,合金只启动η相析出序列,故时效硬化行为表现出明显的双峰特征;而Al5.0Zn3.0Mg合金固溶时形成的a-Al-Zn-Mg和a-Al-Mg-Zn-Mg-Al两种固溶体分别为η相和T相析出序列GP区的形成提供了条件,合金时效时同时启动了时效进程不同、强化相析出与转变时间及其强化作用不同的η相和T相两个析出序列,故Al5.0Zn3.0Mg合金时效硬化双峰特征不明显。     

AgCuZnNi合金铸态组织及凝固路径分析

采用扫描电子显微镜、能谱仪以及X射线衍射等技术,对Ag-18Cu-30Zn-2Ni合金的铸态组织、相组成及结构进行了分析。结果表明,合金主要由白色基体、细小片层状共晶胞及直径为2~6μm的黑色颗粒相组成;铸态合金的物相组成为面心立方(fcc)晶格结构的Ag基固溶体相、灰色层状共晶相(Ag+Cu64Zn36)及简单立方(sc)晶格结构的近球形黑色颗粒Cu2Ni Zn相;Ag Cu Zn Ni合金的平衡凝固路径为:L→L+γ→(L+α1)+γ→((α2+β)+α1)+γ。     

常压及高压凝固Al-Mg及Al-Mg-Zn合金中Al相的固溶体结构

采用X射线衍射仪、能谱仪和透射电镜分别对Al-9.6%Mg合金、Al-11Mg-4.5Zn合金和Al-17Zn-1.5Mg合金常压及6 GPa高压凝固后Al相的固溶体结构进行研究。结果表明:6GPa高压凝固后,Al-9.6%Mg合金中Mg在Al相中的固溶度显著增大;在Al-11Mg-4.5Zn合金和Al-17Zn-1.5Mg合金中,Mg、Zn溶质在Al相中的固溶度均增大,但Zn比Mg固溶的比例要大得多。在常压凝固条件下,与纯铝相比,3种合金中Al相的晶格常数均增大。与常压凝固相比,高压凝固Al-9.6Mg合金和Al-11Mg-4.5Zn中Al相晶格常数分别增大了1.178%和0.220%;在Al-17Zn-1.5Mg合金中,Al相晶格常数变化很小。此外,在Al-Mg-Zn合金中,原子半径较大的Mg固溶到Al相中,导致其晶格常数增大,原子半径较小的Zn固溶到Al相中,导致其晶格常数减小,且高压凝固后,溶质的原子半径越小,在Al相中固溶的比例越大。     

Pb-Bi-Sn准包晶合金定向凝固微观组织演化

采用液态金属冷却定向凝固结合液淬法,在温度梯度为18 K/mm、凝固速度为0.5～100 μm/s的条件下系统研究了Pb-30％Bi- 18％Sn准包晶合金的微观组织演化及溶质分布规律.主要从凝固路径、相组成、溶质分布及微观组织特征等几个方面来研究Pb-Bi-Sn准包晶合金定向凝固过程的组织演化.其中,准包晶合金的凝固路径通过DSC差热分析的方法进行研究,发现其凝固路径为:L→L+α-Pb→L+α-Pb+β-Pb7Bi3→L+α-Pb+β-Pb7Bi3+Sn→ (β-Pb7Bi3+Sn)共晶.结合XRD,分析定向凝固试样的相结构,结果表明:试样由具有面心立方结构的α-Pb相、密排六方结构的β-Pb7Bi3相和体心正方结构的(Sn)相构成.在Pb-Bi-Sn合金定向凝固过程中,当凝固速度为0.5～2 μm/s时,初生α-Pb相以胞状界面生长,而当凝固速度增大至5μm/s及以上时,初生α-Pb相将由胞状转变为枝晶状界面生长.利用能谱分析仪对定向凝固试样进行溶质分布测试,发现局部出现溶质偏析,导致共晶组织(β-Pb7Bi3+Sn)出现.     

Effect of trace rare earth element Er on Al-Zn-Mg alloy

1 Introduction Remarkable effects of rear-earth elements on aluminium alloys, such as eliminating impurities, purifying melt, refining as-cast structure, retarding recrystallization and refining precipitated phases, have been widely researched for a long…     

Influences of Initial Compositions,Dendrite Morphologies and Solid-Back Diffusion on Solidification Path of Al-Si-Mg Alloys

The solidification paths of ternary eutectic Al-Si-Mg alloys in the Al-rich corner were investigated by numerical calculation. The thermodynamic data needed in the calculation were obtained by direct coupling simulation program with a CALPHAD software Thermo-Calc via its TQ6-interface and COST2 database. The influences of the initial compositions, dendrite morphologies and the solid diffusion coefficients on the solidification path were analyzed. The solidification paths were calculated with assumed different solid diffusion coefficients varying in eight orders of magnitude and different dendrite morphologies including the five basic geometrical shapes of spherical, cylindrical, plate-like, inward cylindrical, inward spherical and the assumed equiaxed dendrites. The calculated results comparisons showed that initial compositions, dendrite morphologies and solid-back diffusion can significantly influence the solidification path and the type and amounts of eutectic of Al-Si-Mg alloys. The predicted solidification paths and the eutectic fraction of selected Al-Si-Mg alloys calculated with assumption of equiaxed dendrite morphology agreed well with the experimental results.     

As-cast microstructure of Al-Zn-Mg and Al-Zn-Mg-Cu alloys added erbium

1 INTRODUCTIONMany researches show that the properties ofaluminum and its alloys can be remarkablyi mproved withreasonable rare earth additions .Theactions of rare earth elements in the aluminumalloys consist in alterant-agent , micro-alloying andso on[1 3].By far element scandiumis the most ef-fective rare earth element which i mproves thealuminum alloys properties[4 6]. However , theprice of scandiumis very high.Therefore ,it s veryessential to find a new rare earth element , whichacts …     

Development of High Strength and Toughness Non-Heated Al–Mg–Si Alloys for High-Pressure Die-Casting

Based on the 3 factors and 3 levels orthogonal experiment method, compositional effects of Mg, Si, and Ti addition on the microstructures, tensile properties, and fracture behaviors of the high-pressure die-casting Al-x Mg-y Si-z Ti alloys have been investigated. The analysis of variance shows that both Mg and Si apparently infl uence the tensile properties of the alloys, while Ti does not. The tensile mechanical properties are comprehensively infl uenced by the amount of eutectic phase(α-Al + Mg_2Si), the average grain size, and the content of Mg dissolved into α-Al matrix. The optimized alloy is Al-7.49 Mg-3.08 Si-0.01 Ti(wt%), which exhibits tensile yield strength of 219 MPa, ultimate tensile strength of 401 MPa, and elongation of 10.5%. Furthermore, contour maps, showing the relationship among compositions, microstructure characteristics, and the tensile properties are constructed, which provide guidelines for developing high strength and toughness Al–Mg–Si–Ti alloys for high-pressure die-casting.     

Mg含量对Al-Zn-Mg铝合金组织及性能的影响

通过改变镁的含量,设计了4种不同成分的Al-6.0Zn-xMg合金。采用光学显微镜(OM)、扫描电镜(SEM)、差式扫描量热分析仪(DSC)、硬度、导电率以及室温拉伸等分析测试方法,研究了Mg含量对Al-Zn-Mg合金铸态、均匀化态组织性能及T6态力学性能的影响。结果表明:4种铸态合金组织晶界附近存在大量共晶网状结构与链状第二相,主要为α(Al)+三元T(AlZnMg)相,合金中还存在少量的Al₃(Zr,Ti)相和富铁相,提高Mg含量会使合金组织中的非平衡共晶相增加。合金均匀化处理后空冷,基体内有大量细小弥散的针状η(MgZn₂)相析出,且随着Mg含量的提高,这种针状η(MgZn₂)相的析出数量也逐渐增多。随着Mg含量增加,硬度逐渐增加,导电率逐渐下降,且均匀化态合金的硬度及导电率比铸态的高。4种T6态合金中Al-6.0Zn-2Mg合金的综合力学性能最佳。     

均匀化退火对Mg-3Al-1Zn-2.2/5Sr镁合金中第二相的影响

为研究均匀化退火处理对Mg-3Al-1Zn-2.2/5Sr镁合金中第二相的影响,通过X射线衍射分析(XRD)、扫描电镜观察(SEM)和能谱分析(EDS)等手段,并结合Pandat热力学计算软件,对Mg-3Al-1Zn-2.2/5Sr镁合金均匀化退火后组织中的第二相的类型及形成原因进行了分析。结果表明:经过400℃,15 h(炉冷)的均匀化退火处理以后,合金铸态组织中原本存在的(Mg,Al)17Sr2相中固溶的Al元素所占原子分数有所降低。此外,Sr含量为2.2%(质量分数)的合金组织中可以观察到大量沿(Mg,Al)17Sr2相边缘分布的颗粒状Al4Sr相,而Sr含量为5%的合金中基本观察不到(Mg,Al)17Sr2相的变化。     

新型高强度压铸Al-Si-Mg-Mn合金组织和性能的演变

研究了新型高强度Al-Si-Mg-Mn合金组织和性能的演变。基于JMatPro相图模拟计算,设计了不同共晶体积分数的Al-Si-Mg-Mn合金成分。结果表明,新型Al-Si-Mg-Mn合金压铸后(铸态)的抗拉强度可达230~310 MPa,屈服强度200~240 MPa,伸长率约0.5%。铸态组织中包含α-Al、α-AlFeMnSi、二元(α-Al+α-AlFeMnSi/α-AlFeMnSi+Mg₂Si)、四元(α-Al+α-AlMnSiFe+Mg₂Si+Si)共晶。微观组织观察表明,细小α-AlFeMnSi相和多尺度的共晶组织的形成使得该合金具有高的强度;断口形貌分析发现,合金伸长率较低是较大的气孔以及粗大的第二相直接导致的。     

Cr对Mg-Zn-Al-Cu合金沉淀析出过程的影响

通过SEM、X射线衍射等试验手段,研究了合金元素Cr对Mg-10Zn-2Al-1Cu镁合金显微组织及沉淀析出过程的影响。结果表明,Cr元素能细化试验合金的铸态组织,并能部分打断β-Mg17Al12网状组织,且三元相τ-Mg32(Al,Zn)49、AlMg4Zn11、CeCuAl3及颗粒状Al4Cu9相在晶内呈弥散析出,并形成新相CrSb2。试验合金的时效沉淀过程中显微组织的演变过程为:过饱和固溶体→溶质原子偏聚→呈蠕虫状聚集分布的有序相→过渡相→呈(短)杆状或粒状稳定相。合金元素Cr能加速时效初期原子偏聚和晶核形成速度,增加时效后期析出相的稳定性、抑制析出相的长大。     

基于Thermo-Calc及T-f_S-C_L耦合方法预测Biot≤0.1的合金凝固路径(英文)

将二元合金枝晶凝固传输模型及相应的T-fS-CL耦合求解方法扩展到描述多元合金在Biot≤0.1条件下的凝固。基于提出的扩展模型及算法,提出一种考虑传热影响的预测Biot≤0.1合金凝固路径及微观偏析的方法。该算法与Thermo-Calc热力学计算软件接口程序TQ6相耦合,用于实时计算每次迭代需要的热力学数据。Al-2Si-3Mg三元合金实例计算证实提出的模型及算法和凝固路径与微观偏析预测方法的实用性与可靠性,Al-5.17Cu-2.63Si三元合金凝固实验结果与预测结果的取得较好的一致性。     

Quasi-peritectic solidification reactions in 6xxx series wrought Al alloys

Secondary intermetallic phase formation during directional solidification of two 6xxx series wrought Al alloys at low growth velocities of 5–30 mm/min has been investigated using differential scanning calorimetry, transmission electron microscopy and scanning transmission electron microscopy. Thermodynamic calculations predict that a quasi-peritectic reaction, L+Al₁₃Fe₄ → α-Al+α-AlFeSi, should occur during equilibrium solidification of the alloys. However, no composite Al₁₃Fe₄/α-AlFeSi particles, but composite Al₁₃Fe₄/β-AlFeSi particles and triple phase junctions have been observed for the first time, indicating a divorced metastable β-AlFeSi quasi-peritectic reaction, L+Al₁₃Fe₄ → α-Al+β-AlFeSi. More detailed analysis suggests that the metastable β-AlFeSi quasi-peritectic reaction is more favourable both at nucleation and during growth. No unique orientation relationship was found between primary Al₁₃Fe₄ and peritectic β-AlFeSi. The nucleation and growth of peritectic phases and the morphology evolution of the two intermetallic phases, Al₁₃Fe₄ and β-AlFeSi, are discussed.     

Effect of Cu addition on microstructure and properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy

To improve the strength,hardness and heat resistance of Mg-Zn based alloys,the effects of Cu addition on the as-cast microstructure and mechanical properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy were investigated by means of Brinell hardness measurement,scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),XRD and tensile tests at room and elevated temperatures.The results show that the microstructure of as-cast Mg-10Zn-5Al-0.1Sb alloy is composed of α-Mg,t-Mg32(Al,Zn)49,φ-Al2Mg5Zn2 and Mg3Sb2 phases.The morphologies of these phases in the Cu-containing alloys change from semi-continuous long strip to black herringbone as well as particle-like shapes with increasing Cu content.When the addition of Cu is over 1.0wt.%,the formation of a new thermally-stable Mg2Cu phase can be observed.The Brinell hardness,room temperature and elevated temperature strengths firstly increase and then decrease as the Cu content increases.Among the Cu-containing alloys,the alloy with the addition of 2.0wt.% Cu exhibits the optimum mechanical properties.Its hardness and strengths at room and elevated temperatures are 79.35 HB,190MPa and 160MPa,which are increased by 9.65%,21.1% and 14.3%,respectively compared with those of the Cu-free one.After T6 heat treatment,the strengths at room and elevated temperatures are improved by 20% and 10%,respectively compared with those of the as-cast alloy.This research results provide a new way for strengthening of magnesium alloys at room and elevated temperatures,and a method of producing thermally-stable Mg-10Zn-5Al based high zinc magnesium alloys.     

MICROSTRUCTURE AND MACROSEGREGATION OF Al-7%Si ALLOY SOLIDIFIED UNDER COMPLEX EFFECTS OF ELECTROMAGNETIC AND CENTRIFUGAL FORCES

1.IntroductionElectromagneticcentrifugalcasting(EMCC)isanewtechnologydevelopedfromcentrifUgalcastingandelectromagneticstirringprocessing.WithaseeofEMFgeneratingdeyicemountedonacentrifugalcastingmachine,liquidmetalssolidifyunderthecomplexeffectsofEMFandcentrifugalforce.ThequalityofthecastingsiscontrolledbymodifyingtheparametersofEMFandcentrifugalcasting.Thistechnologyprovedveryeffective...inimprovingthemacrostructureandpropertiesofthecastings['].WiththeeffectoftheEMF,thereisalwaysaconve…     

Thermo-Calc based multi-component micro-segregation model and solidification paths calculations

On the basis of a multi-length scale modeling,a mixture-averaged multi-component/multiphase microsegregation model was proposed without pre-set function for the micro-scale solute profile.The model exp...     

Effects of Cu content on microstructure and mechanical properties of rheo-diecasting Al-6Zn-2Mg-xCu alloys

A systematic study on how Cu content affects the microstructure and mechanical properties of rheo-diecasting Al-6Zn-2Mg-xCu alloys during solution treatment and ageing heat treatment was conducted. The swirled enthalpy equilibrium device (SEED) was adopted to prepare the semi-solid slurry of Al-6Zn-2Mg-xCu alloys. The microstructure development and mechanical properties were studied using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), as well as hardness and tensile testing. The grain boundary and shape factor were calculated using image processing software (Image-Pro Plus 6.0). Results show that the alloys are composed of typical globular primary α-Al grains, eutectic phases, and smaller secondary α-Al grains. After solution and ageing heat treatment, the eutectic phases are dissolved into Al matrix when the Cu content is lower than 1.5wt.%, while some eutectic phases transform into Al₂CuMg (S) phases and remain at grain boundaries when Cu content reaches 2wt.%. T6 heat treatment significantly enhances the mechanical properties of rheo-diecasting Al-6Zn-2Mg-xCu alloys. When Cu concentration is 0.5wt.%–1.5wt.%, the ultimate tensile strength, yield strength and elongation of T6 treated alloys rise to around 500 MPa, 420 MPa, and 18%, respectively.

     

Mg和Cu在Al-Zn-Mg合金时效初期的Monte Carlo模拟

采用Monte Carlo方法模拟研究Al-6Zn-(2Mg)和Al-10Zn-1.9Mg-(1.7Cu)合金时效初期微观结构的演变过程,并分析Mg和Cu的基本作用。结果表明:时效初期,Al-6Zn合金中的Zn原子有较强的团聚倾向,形成了明显的Zn原子簇;而在Al-6Zn-2Mg合金中出现明显的Zn原子簇、Zn-Mg原子簇及少量的Mg原子簇。Mg的作用是通过Mg和Zn原子间强烈的相互作用形成Zn、Mg原子交替排布的短程有序结构。含铜的Al-10Zn-1.9Mg-1.7Cu合金中,不仅形成了Zn原子簇、Mg原子簇和Zn-Mg原子簇,还形成了少量Zn-Cu原子簇、Mg-Cu原子簇和Zn-Mg-Cu原子簇。Cu的存在促进Zn原子和Zn-Mg原子团簇化,但对Mg原子的团簇化影响不大。