炉膛温度对定向凝固Al—Cu合金热裂的影响

采用半定量等级评定方法，研究了炉膛温度变化对定向凝固Ａｌ－０．６％Ｃｕ和Ａｌ－２．０％Ｃｕ两种合金热裂倾向的影响。定向凝固冷却曲线的测量和热裂形式的凝固分析表明：定向凝固过程中合金的不可补缩长度对热裂纹的形成有重要影响。     

晶界状态对合金热裂倾向的影响

进行了定向凝固Ａｌ－Ｃｕ合金和Ｒｅｎｅ１２５合金晶界状态分析，并与合金热裂倾向性试验结果对比，揭示了晶界状态对合金热裂倾向的影响。     

化学成分对定向凝固Al—Cu合金热裂倾向的影响

本文提出了热裂倾向评定的半定量等级标准，并进行了不同成分Ａｌ－Ｃｕ合金定向凝固热裂试验。理论计算与试验结果比较，证实了化学成分对定向凝固合金热裂倾向的影响符合凝固过程的收缩补偿理论，以及柱晶组织对形成晶间搭桥的影响。     

化学成分对定向凝固Al－Cu合金热裂倾向的影响

本文提出了热裂倾向评定的半定量等级标准，并进行了不同成分Ａｌ－Ｃｕ合金定向凝固热裂试验。理论计算与试验结果比较，证实了化学成分时定向凝固合金热裂倾向的影响符合凝固过程的收缩补偿理论，以及柱晶组织对形成晶间搭桥的影响。     

Y对铸造Ni3Al基合金组织和力学性能的影响

研究了Ｙ对定向和非定向铸造Ｎｉ３Ａｌ基合金Ｎｉ－９．０Ａｌ－８．０Ｃｒ－１．７Ｚｒ－０．０６Ｂ（ｗｔ％）不同温度下瞬时拉伸性能的影响。结果表明，Ｙ能提高定向凝固合金的韧性，降低合金的屈服强度；而对非定向凝固合金，Ｙ全面恶化合金的力学性能，即使０．０３％Ｙ的加入量，其危害性也是非常明显的。     

Cu基形状记忆合金的时效

对比研究了时效对亚共析Ｃｕ－１２．０Ａｌ－５．０Ｎｉ－２．０Ｍｎ－１．０Ｔｉ（ｗｔ．－％）合金与Ｃｕ－２０．０Ｚｎ－６．０Ａｌ－微量Ｂ（ｗｔ．－％）合金热稳定性的影响。结果表明，无论在母相状态或马氏体相状态，Ｃｕ－Ａｌ－Ｎｉ合金的时效热稳定性均远优于Ｃｕ－Ｚｎ－Ａｌ合金。Ｃｕ－Ａｌ－Ｎｉ合金母相状态时效伴随着ＤＯ＿３有序畴长大，基体中Ａｌ、Ｎｉ、Ｍｎ等元素贫化，导致Ｍ＿ｓ点升高，马氏体转变量降低。Ｃｕ－Ｚｎ－Ａｌ合金母相状态时效伴随贝氏体转变，引起基体富Ｚｎ富Ａｌ，导致Ｍ＿ｓ点下降，马氏体量降低。Ｃｕ－Ａｌ－Ｎｉ合金高的时效热稳定性可能来源于Ｎｉ对Ａｌ、Ｃｕ等原子扩散的阻碍作用。     

晶界状态对定向凝固Al—Cu和Renel25合金热裂倾向的影响

在ＨＲＳ定向凝固设备上进行了合金热裂试验,采用半定量方法评定了定向凝固Ａｌ－Ｃｕ和Ｒｅｎｅｌ２５合金热裂倾向。观察了合金的晶界,并分析讨论了其对合金热裂的影响。用晶界状态分析的结果与试验结果完全一致。证明了晶界状态对热裂纹的形成有重要影响,其影响包括对晶间结合力的破坏作用和对晶界凝固收缩的补偿作用。晶界状态对热裂影响的综合作用取决于晶界低熔点相的分布和数量。     

混合稀土对改善铝铜合金铸造性能的影响

通过研究混合稀土变质后铸造性能的变化，得出了Ａｌ－４．５％Ｃｕ合金流动性，线收缩率，热裂倾向，缩松及夹杂物等随稀土加入量的变化规律，知获得最佳综合铸造性能的最佳混合稀土加入量为０．２％，对混合土变质后的Ａｌ－４．５％Ｃｕ合金铸造性能的改善机制进行了分析，认为混合稀土之所以能改善合金的铸造性能，是因为改变了合金的凝固结晶特性，并使合金获得了净化。     

凝固收缩补偿与合金的热裂倾向

在总结前人热裂纹研究的基础，提出了热裂纹形成的凝固收缩补偿模型，该模型将合金凝固过程按收缩补偿方式分为准液相区，可补缩区，不可补缩区，晶间塔桥四个阶段，热黎明纹形成于不可补缩区，晶间液相收缩产生孔洞，并在进一步收缩过程中扩展为热裂纹，利用等径圆柱和等径圆球模型计算出理想状态下柱状晶和等轴晶不可补缩区液相体积分数范围分别为０．３１％－９．３％和０．８３％－２６％，对Ａｌ－Ｃｕ合金和Ａｌ－Ｓｉ合金不可     

Cu,Fe元素呈对喷射成形Al98—3xCu2xFexNi1Ce0.5Zr0.5合？…

采用喷射成形技术制备了不同成分的Ａｌ９８－３ｘＣｕ２ｘＦｅｘＮｉ１Ｃｅ０．５Ｚｒ０．５（摩尔分数,％）合金快速凝固材料,重点研究了Ｃｕ,Ｆｅ元素含量对合金微观组织,力学性能以及断裂机制的影响。研究结果表明,ｘ〈２时,可有效避免粗在的Ａｌ７Ｃｕ２Ｆｅ平衡相形成;ｘ＝１．５时,合金具有较好的综合力学性能,合金的抗拉强度,屈服经度、延伸率和弹性模量分别可达６４３ＭＰａ,５５８．４ＭＰａ,８．４％和８０．     

Determining hot cracking index of Al–Si–Cu–Mg casting alloys calculated using effective solidification range

The possibility of determining the hot cracking index using the calculated value of the effective solidification range is investigated for multicomponent cast aluminium alloys based on the system Al–Si–Cu–Mg with Mn, Ni, Fe and Zn additives. The upper limit of the effective solidification range was calculated as the temperature of formation of 65 wt-% solid phase using Sheil model. The linear relationship of the hot cracking index and the effective solidification range in the industrial and experimental multicomponent alloys based on the Al–Si–Cu–Mg system is demonstrated.     

Microstructure and Tensile/Corrosion Properties Relationships of Directionally Solidified Al–Cu–Ni Alloys

Al–Cu–Ni alloys are of scientific and technological interest due to high strength/high temperature applications, based on the reinforcement originated from the interaction between the Al-rich phase and intermetallic composites. The nature, morphology, size, volume fraction and dispersion of IMCs particles throughout the Al-rich matrix are important factors determining the resulting mechanical and chemical properties. The present work aims to evaluate the effect of the addition of 1wt%Ni into Al–5wt%Cu and Al–15wt%Cu alloys on the solidification rate, macrosegregation, microstructure features and the interrelations of such characteristics on tensile and corrosion properties. A directional solidification technique is used permitting a wide range of microstructural scales to be examined. Experimental growth laws relating the primary and secondary dendritic spacings to growth rate and solidification cooling rate are proposed, and Hall–Petch type equations are derived relating the ultimate tensile strength and elongation to the primary dendritic spacing. Considering a compromise between ultimate tensile strength and corrosion resistance of the examined alloys samples from both alloys castings it is shown that the samples having more refined microstructures are associated with the highest values of such properties.     

Reducing welding hot cracking of high-strength novel Al–Mg–Zn–Cu alloys based on the prediction of the T-shaped device

ABSTRACT

The higher hot cracking tendency during fusion welding in traditional high-strength 7000 series alloys has been an obstacle for its further application. In this study, the cracking susceptibility can be suppressed by fabricating Al–Mg–Zn–Cu alloys with Zn/Mg≤1 and Cu/Mg≤0.25 while simultaneously maintaining the high strength. A T-shaped device combined with non-equilibrium solidification is developed to simulate the solidification during fusion welding, and it is effective to predict the shrinkage load, temperature and solid fraction. The effect of solidification temperature range, the amount of eutectics at the terminal stage of solidification and the shrinkage load during solidification on the hot cracking susceptibility are discussed in detail.     

Influence of Liquid Film Characteristics on Hot Cracking Initiation in Al-Cu Alloys at the End of Solidification

In this study, Al-4Cu alloy specimens with spherical grains and liquid films were obtained by isothermal reheating treatment. The hot cracking of the solidification process was determined using a modified constrained rod casting experimental apparatus, and the effect of liquid film characteristics at the end of solidification on hot cracking initiation of Al-4Cu alloys was systematically investigated by combining molecular dynamics simulations and other methods. With the extension of soaking time, the liquid fraction (liquid film fraction at the end of solidification) and grain shape factor increased with higher isothermal reheating temperatures. Additionally, the widened filling channel decreased the hot cracking initiation temperature and the critical hot cracking shrinkage stress was found to increase, thus reducing the hot cracking severity in Al-4Cu alloys. Molecular dynamics simulations revealed that with the extension of soaking time, the composition of the liquid film changed at different isothermal reheating temperatures, but the short-range structure and atomic ordering of the liquid film remained the same. The activity of the liquid film increased in equilibrium, leading to a decrease in viscosity and an increase in fluidity, which contributed to the filling behaviour. After isothermal reheating at 640 °C for 60 min, the liquid fraction reached the maximum, and the viscosity of the liquid film was the minimum. In addition, almost no hot cracks were found.     

Influence of scandium on weldability of 7010 aluminium alloy

Abstract

The commercial 7000 series aluminium alloys are based on medium strength Al–Zn–Mg and high strength Al–Zn–Mg–Cu systems. The medium strength alloys are weldable, whereas the high strength alloys are non-weldable. This is because the amount of copper present in these alloys gives rise to hot cracking during solidification of welds. As a result, the high strength Al–Zn–Mg– Cu base alloys are not used for applications where joining of components by welding is an essential step. In the present study, using a combination of qualitative Houldcroft test and quantitative Varestraint test, it is shown that a small addition of scandium to the commercial 7010 alloy reduces the hot cracking susceptibility during solidification of welds produced by the gas tungsten arc welding process. The improvement in weldability is found to be the result of the considerable grain refinement in the weld structure following the scandium addition. The results of microhardness and tensile tests are further described within the context of the present work to demonstrate that the 7010+Sc welds also exhibit a combination of improved strength and ductility.     

Determining hot cracking index of Al–Mg–Zn casting alloys calculated using effective solidification range

The possibility of determining the hot cracking index using the calculated value of the effective solidification range is investigated for multicomponent cast aluminium alloys based on the Al–Mg–Zn system with Mn, Ni, Fe and Si additives. The upper limit of the effective solidification range was calculated as the temperature of formation of a 65?wt-% solid phase using the Sheil model. The linear relationship of the hot cracking index and the effective solidification range in the industrial and experimental multicomponent alloys based on the Al–Mg–(Zn) system is demonstrated.     

脉动磁场对Al—Cu合金热裂的影响

用对比的方法，研究了脉动磁场对ＡｌＣｕ合金热裂倾向性的影响。实验结果表明：脉动磁场具有缩小ＡｌＣｕ合金有效结晶区间、减小有效结晶区间线收缩之功能，有效地降低了ＡｌＣｕ合金热裂倾向性；磁场频率的影响为：ｆ＝１９５Ｈｚ时热裂纹最小，ｆ＞３７．５Ｈｚ时影响不大。     

Al-Cu-Co十次准晶颗粒增强铝基复合材料的微观组织和制备中的相转变

采用电弧炉熔炼配置成分为Al65Cu15Co20十次准晶合金锭,并以Al65Cu15Co20准晶颗粒为增强相,Al-4.5%Cu合金为基体,采用熔体机械搅拌法制备准晶颗粒增强铝基复合材料.利用XRD、SEM及EDS分析Al65Cu15Co20准晶合金及颗粒增强铝基复合材料的相成分、微观组织及各组成相的分布,并详细分析准晶颗粒加入熔体前后的形貌、相成分和结构的变化.由于准晶颗粒与熔体之间的相互扩散作用,使得准晶颗粒加入熔体后迅速失稳,其形貌则由加入前的不规则多边形状转变成块状和板条状,并发生如下相转变:D-Al62.10Cu17.46Co20.44→θ-Al79.58Cu1.10Co19.32,在随后的凝固过程中,由于"界面推移效应"使得θ相沿晶界处均匀分布.