微量Ce对亚快速凝固Al-Zn-Mg-Cu合金组织与性能的影响

通过DSC,XRD,SEM,EDS,静拉伸实验等材料分析方法研究了Ce对亚快速凝固方式铸造Al-Zn-Mg-Cu合金显微组织与力学性能的影响,探求合理的均匀化热处理工艺。结果表明,添加Ce能减小合金枝晶间距,细化晶粒,消除分散缩孔,起到细晶和净化的作用。添加Ce使合金低熔点共晶相的初熔温度降低3℃,相同均匀化条件下微量Ce能促进低熔点共晶相溶入基体,改善合金的均匀化效果。合金A的均匀化温度应低于480℃,合金B的均匀化温度应低于470℃,添加Ce降低了合金的均匀化温度,提高均匀化效率。添加Ce还大幅度提高了合金抗拉强度。     

快速凝固高温铝合金显微组织及热稳定性研究

本文研究了快速凝固Al90.5Fe4.0Cu2.0Ce1.0Zr0.5Ti0.5V0.4Si1.1(at%)高温铝合金的显微组织及其热稳定性.结果表明,合金存在三种基本组织,即胞晶和显微胞晶组织、共晶组织、弥散析出相.350℃等温退火后,胞晶组织发生分解,弥散强化相Al12(Fe,V)3Si和Al17Cu5Ce2Fe的数量明显增多,并有一定数量的Al3(Zr,Ti)相析出.400℃以上温度热处理时,弥散相Ai17Cu5Ce2Fe发生部分分解,形成Al7Cu2Fe相.     

Al和Ce的含量对Mg-Al合金组织的影响

研究了Al和Ce的含量对Mg-Al-Ce合金组织的影响以及第二相的演变规律,进行热力学计算分析探讨了合金化合物的形成规律及其作用。结果表明:添加适量的Ce对Mg-Al合金有细化晶粒的作用,当Al的添加量(质量分数,下同)为2.5%、Ce的添加量为2%时晶粒最小,为280μm。数据拟合结果表明,Al含量为6.4%~7%、Ce含量为1.6%~2%为最佳添加量,可使晶粒尺寸减小到160μm。随着Al、Ce含量的变化合金中优先生成Al4Ce相,在凝固过程中细小的Al4Ce化合物吸附在α-Mg晶粒周围形成片层状共晶,阻碍α-Mg晶粒的长大从而细化合金晶粒。     

原位观察不同冷却速率下GH3625合金的凝固过程

利用带有红外加热炉的共聚焦激光扫描显微镜(CLSM)对GH3625高温合金在不同冷却速率(30℃/min、100℃/min和200℃/min)下的凝固过程进行了动态原位观察,通过差示扫描量热分析仪(DSC)、扫描电镜(SEM)和能谱仪(EDS)研究了凝固后的组织形态及相的析出规律。结果表明,GH3625合金的液相线温度在1 356.5℃,在凝固过程中自由表面液相分数随温度和时间的变化关系满足Avrami方程;凝固过程中主要相的析出顺序依次为γ基体相、碳化物和Laves相;在GH3625合金凝固过程中,随着冷却速率的增大,枝晶细化,枝晶间距减小,成分偏析减轻,Laves相分布更加弥散,且以析出共晶Laves相为主;凝固末期大量的Nb元素富集在枝晶间和晶界,这是形成Laves相的主要原因。     

Mg对共晶Al-2%Fe合金显微组织的影响

为了消除粗大针状富铁相对Al-Fe合金组织和性能的不良影响,在金属型铸造共晶Al-2?合金中添加了质量分数为0.2%一0.8%的合金元素Mg,利用光学显微镜和电子探针研究了Mg对共晶合金组织以及富铁相形态的影响.研究结果表明:共晶Al-2?合金组织为针状Al3Fe相与(α-Al)相所组成的非规则共晶组织;添加Mg后,合金组织转变为由树枝状初生(α-Al)和枝晶间网状分布共晶体所组成的亚共晶组织,富铁相尺寸显著降低;随着Mg添加量的增加,初生(α-Al)枝晶二次枝晶间距增大,一次枝晶出现熔断.     

定向凝固Cu-Cr自生复合材料的微观组织演变

为了研究定向凝固Cu-Cr自生复合材料的微观组织构成及其在不同凝固速度条件下的组织演变,在高梯度定向凝固装置上制备了Cu-1.0%Cr、Cu-1.7%Cr(质量分数)两种成分的Cu基自生复合材料,采用金相显微镜、扫描电镜以及能谱分析进行了微观组织观察和相的成分分析.研究表明:Cu-1.0%Cr亚共晶合金定向凝固组织为初生α相和棒状(或针状)共晶体(α β)的混合组织;Cu-1.7%Cr过共晶合金为α相、初生β相和共晶(α β)的混合组织;随着凝固速度的提高,α相一次胞(枝)晶逐渐细化,晶间距逐渐减小;共晶体(α β)分布在α相胞(枝)晶间,起到强化基体的作用;初生β相呈颗粒状不均匀地分布在α相基体上.     

Mg对共晶Al-2％Fe合金显微组织的影响

为了消除粗大针状富铁相对Al-Fe合金组织和性能的不良影响，在金属型铸造共晶Al-2％Fe合金中添加了质量分数为0．2％～0．8％的合金元素Mg，利用光学显微镜和电子探针研究了Mg对共晶合金组织以及富铁相形态的影响．研究结果表明：共晶Al-2％Fe合金组织为针状Al3Fe相与（α-Al）相所组成的非规则共晶组织；添加Mg后，合金组织转变为由树枝状初生（α-Al）和枝晶间网状分布共晶体所组成的亚共晶组织，富铁相尺寸显著降低；随着Mg添加量的增加，初生（α-Al）枝晶二次枝晶间距增大，一次枝晶出现熔断。     

深冷处理对快冷Mg-6Al-1Y合金等温时效析出的影响

采用铜模喷铸与等温时效相结合,探讨了深冷处理对非平衡凝固Mg-6Al-1Y合金组织及其沉淀析出行为的影响。结果表明,原始快冷合金的凝固组织由细小不发达花瓣状α-Mg基体相、晶界离异共晶β相和Al2Y稀土相所组成。深冷过程中引起的微应力及塑性变形有利于凝固组织细化,同时形成高密度位错结构。经250℃/4 h时效处理后,快冷合金的晶界处发生不连续沉淀,所析出的针片状β相择优生长,并与基体保持良好的共格关系。深冷处理有效促进快冷合金中β相的析出,有利于晶内连续沉淀形成并改善析出相形貌为短棒状,合金显微硬度高达77.2HV,相比原始快冷合金提高23.1%。     

离心压力和冷却速度对AZ91镁合金凝固组织的影响

旨在优化AZ91镁合金凝固组织,通过OM和XRD设备研究了不同离心压力和冷却速度对AZ91镁合金凝固组织演变的影响,结果表明,随着离心压力的增大,合金晶粒尺寸细化,第二相β(Mg12Al17)析出量减少,不保温试样,β相形态由粗大连续网状向细小断续状转变,保温试样,β相为粒状弥散分布晶内,压力增大,颗粒数量减小,粒径细化.同等凝固压力下,增大冷速,一次β相析出量增多,二次β相析出量减少.XRD分析表明,增大离心压力β相峰值略微减弱,α-Mg的晶格常数减小.     

Zr元素及冷却速度对Mg-12Sm合金凝固组织的影响

研究了Mg-12Sm合金在不同冷却条件和添加Zr元素前后凝固组织的变化规律,实验发现水冷模具浇注下冷却速度提高,晶粒细化,二次枝晶臂间距减小,晶间共晶组织体积变小,但总体积分数和分布并没有明显改变;添加0.1%(质量分数)Zr后,晶粒明显细化,树枝晶转化为等轴晶,二次枝晶臂间距减小,晶间共晶组织体积分数增大,共晶组织形貌和分布没有明显变化;Mg-12Sm和Mg-12SmZr合金水冷后Mg基体中Sm含量降低。     

Impurity effects on the nucleation and growth of primary Al3(Sc,Zr) phase in Al alloys

Impurity effects on the nucleation and growth of primary Al₃(Sc,Zr) phase have been investigated in high purity Al alloys and commercial purity Al alloys, respectively. In the case of high purity Al alloys, primary Al₃(Sc,Zr) phases were found to be pushed to grain boundaries ahead of the solidification front. Such type of primary Al₃(Sc,Zr) phase did not contribute to the heterogeneous nucleation, and thereby the grain refinement of Al alloys. In the case of commercial purity Al alloys, the presence of Fe, Si, Cu, Mg, Ti, and other impurities significantly enhanced the heterogeneous nucleation of primary Al₃(Sc,Zr) phase. Most primary Al₃(Sc,Zr) phases were found to be located within the α-Al matrix, and kept an identical orientation relationship with the α-Al matrix. Furthermore, the presence of the impurities also changed the growth mode on the primary Al₃(Sc,Zr) phase. In the case of commercial purity Al alloys, a peritectic to eutectic reaction was induced due to the presence of the impurities. A layered growth was observed leading to a narrow particle size distribution. In contrast, in the case of high purity Al alloys, a featureless structure was observed. This investigation demonstrates that impurities and their concentrations are important factors affecting the nucleation and growth of primary Al₃(Sc,Zr) phases, and thereby for the successful grain refinement in Al-based alloys.     

Sb对Mg-5Al-2Sr合金组织和性能的影响

采用表面活性元素Sb微合金化的方法制备了Mg-5Al-2Sr-xSb(x=0,0.3,0.6,1.0)合金,通过金相显微镜、X射线衍射仪、扫描电镜和力学性能测试等方法研究了Sb含量对Mg-5Al-2Sr合金微观组织和力学性能的影响.结果表明,Mg-5Al-2Sr-xSb合金铸态组织主要由枝晶α-Mg、沿晶界或分布在枝晶间的层状或离异共晶的Al4Sr相、块状三元Mg9Al3Sr相(τ相)和颗粒状SbSr2相组成,随着Sb含量的增加,Sb-Sr2相的数量逐渐增多,τ相逐渐减少.Sb的质量分数为0.6%时,断续分布的Al4Sr相和细小弥散分布的Sb-Sr2相能够提高Mg-5Al-2Sr合金的室温和高温(150℃)机械性能.     

基于高温熔凝法Al_2O_3/ZrO_2/YAG共晶陶瓷显微组织演变规律

作为超高温结构材料,共晶氧化物陶瓷的力学性能和显微组织密切相关。采用高温熔凝法制备Al_2O_3/ZrO_2/YAG共晶陶瓷体,研究熔体温度和结晶种子对凝固组织影响规律,运用经典形核机制和Jackson-Hunt共晶生长模型探讨了凝固组织的演变机理。研究表明,随着熔体温度升高(1750~2000℃),凝固体物相组成从α-Al_2O_3,c-ZrO_2和YAG转变为α-Al_2O_3,c-ZrO_2和亚稳相YAP。凝固组织依次经历:非共晶Al_2O_3/ZrO_2/YAG、不规则共晶Al_2O_3/ZrO_2/YAG、纳米纤维状共晶Al_2O_3/ZrO_2/YAG和复杂粗大的亚稳复合陶瓷Al_2O_3/ZrO_2/YAP。分析表明,凝固组织的演变源于异质晶核点不断钝化导致形核过冷度和凝固路径改变,所以合理选择熔体温度和结晶种子是共晶组织调控的关键。     

Influence of Cerium on Microstructure and Solidification of Eutectic Al–Si Piston Alloy

Thermal analysis has become very important in foundry because it aids in studying the effect of additives on eutectic growth temperature and assessing the quality of modifications. This research was performed to investigate the influence of the addition of Ce (0.1–1.0 wt.%) on the eutectic Al–Si–Cu–Mg alloy characteristics of solidification. Field emission scanning electron microscopy (FESEM) and optical microscopy were employed to characterize the alloy microstructure. The main phases studied were the Al–Cu (Al₂Cu) and Al–Si phases. The addition of Ce decreased the nucleation and growth temperatures and acted as a refiner for the alloy. The larger amounts of Ce significantly impacted the Si structure: the average Si particle size decreased as the Ce concentration was increased, which led to a finer grain structure. The Ce formed intermetallic compounds with the alloyed elements that had plate- or needle-like structures and that interrupted the modification of Si. The solidification parameters, including the growth and nucleation temperatures, increased with increasing change in the morphology of the Al–Cu phase that were caused by Ce addition.     

退火态激光选区熔化成形AlSi10Mg合金组织与力学性能

AlSi10Mg合金具有高比强度、高耐磨性等优良特点。由于其成分接近共晶点,成形性能良好,被广泛应用于激光选区熔化技术。然而其热处理制度仍然沿用传统铸态合金的热处理规范,影响了其性能的充分发挥。本工作采用激光选区熔化技术制备了AlSi10Mg合金,并研究了沉积态和后续热处理过程中组织演化规律及其对室温力学性能的影响机制。研究发现：沉积态组织由沿沉积方向生长的α-Al柱状枝晶及枝晶间网状Al-Si共晶组成,具有强烈的〈100〉方向织构,沉积层由三部分组成,分别是细晶区、粗晶区及热影响区,抗拉强度389.5 MPa,伸长率4%。退火过程中,共晶Si破碎、球化,基体中过饱和Si不断析出长大。当退火温度从200 ℃提高到500 ℃时,Si颗粒发生Ostwald熟化,平均尺寸增长了23倍。经过300 ℃和500 ℃退火处理后,试样抗拉强度分别为287.0 MPa和268.0 MPa,但伸长率分别提高到10.3%和17.2%。     

Modification of β-Al5FeSi Compound in Recycled Al-Si-Fe Cast Alloy by Using Sr, Mg and Cr Additions

The effects of Sr,Mg,Cr,Sr/Mg and Sr/Cr combined additions on the Fe-containing intermetallic phase in a recycled Al-Si-Fe cast alloy are investigated.The experimental results show that the additions of Cr and Sr/Cr successfully modified the platelet and flake-likeβ-Al-5FeSi phases （β-compound） into the fibrousα-Al-8Fe-2Si （α-compound）.The additions of Sr and Sr/Mg were less effective to modify theβ-compound into theα-compound,while the eutectic Si was fully modified into the fibrous morphology.A small secondary dendrite arm spacing （DAS） was found in the Sr-added,Cr-added and Sr/Cr-added alloys,especially in a steel mold.The Sr,Sr/Cr and Sr/Mg combined additions modify the eutectic Si simultaneously.A sludge phase was found in the addition of Cr-added,Sr/Cr-added and Mg-added alloys,especially in the graphite mold casting.The volume fraction ofβ-compounds was decreased by the addition of various modifying elements. The Cr and Sr/Cr combined additions are very effective to modify theβ-compound for the recycled Al-Si-Fe based alloys.     

铸造Mg-3Zn-0.5Cu-0.6Zr镁合金的时效析出行为研究

利用金相显微镜、显微硬度计、X射线衍射仪、扫描和透射电镜研究了铸造Mg-3Zn-0.5Cu-0.6Zr镁合金铸态和固溶时效后的显微组织,初步确定了时效Mg-3Zn-0.5Cu-0.6Zr镁合金中主要合金相的种类和形态.合金铸态组织主要由初晶Mg基体和(Mg+Mg2Cu,CuMgZn)共晶组成.固溶后,晶界处大部分非平衡共晶组织溶解;180℃/20h时效后达到合金时效硬度峰值,此时晶内析出相主要有三类:(1)轴线垂直于(0001)Mg,板条状或棱柱状β2’-MgZn2,长度50nm～200nm,该相是合金的主要时效硬化相;(2)较粗大的、其轴线仍与基面垂直的六棱柱状β2’-MgZn2;(3)轴线平行于(0001)Mg,板条状或针状β-MgZn,长度50nm～150nm.     

Effect of silver addition on formation of secondary phases in squeeze cast Al–Cu–Mg alloys

Abstract

The effect of silver addition on the formation of secondary phases in squeeze cast Al–4.0Cu–1.5Mg and Al–4.0Cu–1.5Mg–0.7Ag (all wt-%) alloys has been investigated using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffractometry, and transmission electron microscopy. The as cast microstructure of both alloys consists of primary dendritic α-Al and various types of secondary solidification phase, e.g. Al₂Cu, Al₂CuMg, Al(Cu,Ag)Mg, and icosahedral (I) and decagonal (D) quasicrystalline phases. However, the solidification path in the interdendritic region during squeeze casting is different for each alloy, i.e. L→ternary α-Al–Al₂Cu–Al₂CuMg eutectic in Al–4.0Cu–1.5Mg and L→L′+Al₂Cu→α-Al–Al₂Cu–Al(Cu_0.75Ag_0.25)Mg eutectic in Al–4.0Cu–1.5Mg–0.7Ag. This indicates that silver acts as an alloying element stabilising the formation of Al(Cu,Ag)Mg Laves phase. The remaining copper and iron rich liquid in the interdendritic region at the final stage of solidification solidifies into a mixed structure of α-Al, Al₂Cu, and AlCuFe I (or D) phases. The composition of the I and D phases, measured by energy dispersive X-ray spectroscopy, is in the range Al–(27～28)Cu–(9～10)Fe and Al–(26～27)Cu–(7～9)Fe (all at.-%) respectively.     

Microstructure and wear characteristics of spray formed and hot extruded Al–Si alloys

Abstract

The microstructural and wear properties of spray formed Al–6.5Si, Al–18Si and Al–18Si–5Fe–1.5Cu (wt-%) alloys have been investigated. The microstructure of the Al–6.5Si alloy exhibits the equiaxed grain morphology of the primary α-Al phase with eutectic Si at the grain boundaries. The size of the primary Si particulates in the Al–18Si alloy varied from 3 to 8 μm embedded in the eutectic matrix. Complex intermetallic phases such as β-Al₅ SiFe and δAl₄ Si₂ Fe are observed to co-exist with primary Si in the spray formed Al–18Si–5Fe–1.5Cu alloy system. The periphery of the preforms invariably showed pre-solidified particles with a large amount of interstitial pores. An extrusion ratio of 6 : 1 for these alloys led to drastic porosity reduction and extensive breaking of second phase particles. These microstructural features showed distinct variation in the wear behaviour and the coefficient of friction of the alloys. The Al–18Si–5Fe–1.5Cu alloy shows better wear resistance compared with the other two alloys, particularly at higher loads. The coefficient of friction shows a dependence upon the applied load. However, this becomes steady at higher loads. The wear behaviour of these alloys is discussed in light of the morphology of debris particles as well as that of the worn surfaces.