含两种尺度微裂纹的高强铝合金的断裂韧性模型

基于高强铝合金在断裂过程中萌生不同尺度微裂纹的机制,用断裂力学建立两种尺度微裂纹影响应力应变场的规律,导出高强铝合金拉伸延性与两种尺度微裂纹的关系,由断裂韧性与拉伸延性的关系建立了高强铝合金断裂韧性与双级微裂纹的非线性关系模型。通过模型解析,分析两种尺度微裂纹体积分数对高强铝合金断裂韧性的影响规律。结果表明:随着一级微裂纹体积分数的增加,材料的断裂韧性开始迅速下降,然后缓慢降低;在较大尺度微裂纹之间萌生小尺度微裂纹,将显著降低合金的断裂韧性。将高强铝合金的结晶相作为一级微裂纹,将弥散相和粗大析出相作为二级微裂纹,预测高强铝合金断裂韧性随两种尺度相(微裂纹)的变化,其规律与实验结果较为吻合。利用模型解析与实验验证结果,提出了改善高强铝合金断裂韧性的组织控制方向。     

含有第二相的高强铝合金疲劳模型

基于疲劳裂纹尖端的应力和应变以及高强铝合金中不同尺度第二相性态对其延性的影响，建立了高强铝合金中粗大第二相、中间尺度第二相以及细小时效强化相性态与其疲劳裂纹扩展速率之间的多元非线性关系模型。结果表明：对于2024铝合金的疲劳扩展速率，该模型的预测趋势与他人的实验研究结果吻合良好。同时借助于对该模型的理论分析，提出了在确保高强铝合金强度不降低的前提下降低其疲劳裂纹扩展速率的优化方案。     

含有不同尺度量级第二相的高强铝合金拉伸延性模型

基于合金中不同尺度第二相在其断裂过程中的作用机制及位错理论 ,建立了高强铝合金中结晶相、沉淀相以及析出强化相性质与其拉伸延性间的多元非线性关系模型。结果表明对于 2 0 2 4铝合金的拉伸延性 ,该模型的预测值与相应的实验值吻合良好。同时借助于该模型的理论分析 ,可以得到在确保高强铝合金强度不降低的前提下提高其延性的优化方案。     

高强铝合金锻件KIC值的测试方法研究

分析对比了国内外高强铝合金锻件的断裂韧性测试方法,并采用不同的技术措施对超大规格或超厚型高强铝合金锻件的断裂韧性值的测试方法进行分析研究,得出了影响高强铝合金锻件KIC测定的具体原因.研究表明,通过一定技术措施,高强铝合金锻件的断裂韧性值KIC是可以采用小尺寸标准CT样获得,并能够通过原材料冶炼和锻造及热处理工艺的改进,提高其断裂韧性值KIC.而影响高强铝合金锻件KIC值成功测定的最根本措施是保证试样裂纹尖端的平面应变状态和塑性变形受到严重约束.     

含有不同尺度微裂纹的铝合金伸长率模型

基于铝合金在变形过程中形成不同尺度的微裂纹,建立了铝合金伸长率与微米级的结晶相及沿晶界分布的亚微米级的弥散相的非线性解析模型,模型的预测与试验值较为符合。借助模型的理论分析,可以定量地得出不同尺度的结晶相,弥散相含量及尺寸对铝合金伸长率的影响。同时,根据模型的解析结果,提出了改善铝合金伸长率的方法。     

近片层γ-TiAl基合金宏观塑性行为的尺度效应

将近片层-γTiAl基合金视为由等轴γ颗粒和多孪晶PST(polysynthetically twinned crystal)单晶颗粒组成的两相复合材料。基于非均质微极介质塑性理论,构建-γTiAl基合金整体有效微极柔度张量,将传统塑性割线模量法推广到微极材料,建立分析和预测-γTiAl基合金的塑性行为尺度效应的细观力学模型。结果表明:-γTiAl基合金的微结构尺度对其宏观塑性硬化行为存在显著的影响;近片层组织-γTiAl基合金中PST晶体颗粒的尺寸越小,合金中硬相夹杂PST颗粒的体积分数越大,合金材料相应的塑性硬化越明显;微极基体的塑性特征尺度与等轴γ晶粒的平均尺寸大小在同一数量级。     

航空用高强铝合金发展新方向

航空用先进铝合金需要高断裂韧性、高疲劳性能、高可成形性和超塑性,以满足部件重量低、损伤容限高和高持久性能的要求。提高铝合金性能的常规方法是以合金化/加工工艺/性能的关系为基础,得出材料的断裂韧性与第二相粒子的平均尺寸和体积分数有关。然而体积分数和粒子平均尺寸只反映第二相的平均形态,并不能构成决定断裂韧性的亚微结构参数。以合金/加工显微结构(主要是第二相粒子)/性能的关系为基础,以2024铝合金为对象研究了断裂韧性和疲劳裂纹扩张速率与合金显微结构参数的关系。配置高杂质和低杂质含量的两种2024合金并加工成5.1mm…     

Al-Zn-Mg-Cu合金多尺度第二相粒子与性能关系研究

介绍了Al-Zn-Mg-Cu合金多尺度第二相粒子与性能关系的研究。涉及的多尺度第二相粒子包括微米尺度的金属间化合物、亚微米尺度的弥散相、纳米尺度的晶内析出相和晶界析出相;涉及的相关性能为强度、断裂韧性以及腐蚀性能。结合相关文献与作者的研究工作,可以得出以下结论:金属间化合物会影响合金的断裂韧性和腐蚀抗力;弥散相通过抑制基体再结晶的方式影响合金的强度、断裂韧性以及腐蚀抗力;晶界析出相会影响合金的断裂韧性和腐蚀抗力;晶内析出相影响合金的强度和断裂韧性。     

Al-Zn-Mg-Cu合金多尺度第二相粒子与性能关系研究（英文）

介绍了Al-Zn-Mg-Cu合金多尺度第二相粒子与性能关系的研究。涉及的多尺度第二相粒子包括微米尺度的金属间化合物、亚微米尺度的弥散相、纳米尺度的晶内析出相和晶界析出相;涉及的相关性能为强度、断裂韧性以及腐蚀性能。结合相关文献与作者的研究工作,可以得出以下结论:金属间化合物会影响合金的断裂韧性和腐蚀抗力;弥散相通过抑制基体再结晶的方式影响合金的强度、断裂韧性以及腐蚀抗力;晶界析出相会影响合金的断裂韧性和腐蚀抗力;晶内析出相影响合金的强度和断裂韧性。     

影响高强铝合金锻件K_(IC)值的材料及组织因素分析

基于高强铝合金自由锻件的研究应用现状,通过对国产锻件的材料因素分析,讨论了高强铝合金国产锻件断裂韧性(KIC)影响规律的内在和外在因素,并结KIC合组织因素及微区成分分析,从影响国产7050锻件KIC的关键因素分析入手,即材料与冶炼因素的分析,来对断裂韧性指标进行综合性评价。研究表明:只有严格控制原材料生产,科学设计锻造和热处理工艺,并调整高强铝合金的强度与塑性指标,使其合理搭配才是提高高强铝合金国产锻件断裂韧性指标的最根本途径。针对国产材料,高强铝合金锻件应考虑维持现有的Cu含量水平下,调整增加Mg含量,同时建议增加Zn含量,并严格控制外来夹杂物的含量、大小和分布。     

Heat treatment-modulated coupling effect of multi-scale second-phase particles on the ductile fracture of aged aluminum alloys

Experiments and multi-scale modeling were carried out in order to study the heat treatment-modulated coupling effect of multi-scale second-phase particles on the ductile fracture of two typical kinds of heat-treatable aluminum alloys, i.e. an Al–Cu–Mg alloy and an Al–Mg–Si alloy. It was revealed experimentally and theoretically that an appropriate combination of the multi-scale second-phase particles, which could be achieved by appropriate cooperation of the heat treatment steps, i.e. the solution, quenching and aging treatments, is necessary and sufficient for obtaining an excellent fracture toughness for the heat-treatable aluminum alloys. The experimental phenomenon, that the alloys containing more detrimental constituents but aged at a somewhat higher temperature exhibit ductility and fracture toughness superior to those of the alloys containing less detrimental constituents but aged at lower temperatures, could be reasonably explained by the cooperative effect of the heat treatment steps. Contours of the fracture toughness with respect to the technological parameters of the heat treatment, e.g. the aging temperature and quench factor, were developed to show the cooperative effect of the heat treatment steps on the fracture toughness of the aged aluminum alloys quantitatively. The good agreement between the calculations and the experimental results indicated that the present modeling is applicable for describing the heat treatment-modulated coupling effect of the multi-scale second-phase particles in aged aluminum alloys.     

Fracture Toughness of Friction Stir-Welded Lap Joints of Aluminum Alloys

The aim of this study is to determine the fracture toughness of friction stir-welded (FSW) lap joints of aluminum alloys. FSW lap joints of AA 2014 and AA 6063 aluminum alloy plates were performed on a conventional semiautomatic milling machine. FSW lap joints were produced on alloy plates. Fracture toughness of FSW lap joints were calculated from the results of tensile shearing tests. New empirical equations were developed for fracture toughness and energy release rate based on the relation between the hardness and fracture toughness values. Fracture toughness of FSW lap joints increases exponentially as the hardness reduces. The results of the experiments showed that the amount of Si content in Al alloys affects the fracture toughness of the FSW lap joints.     

Advanced Aerospace Al Alloys

SiC particulate or whisker-reinforced aluminum alloys are very attractive for applications requiring high stiffness coupled with a comparatively light weight. The dispersion strengthened Al alloys produced through the rapid solidification processing/powder metallurgy route demonstrate superior elevated temperature strength and microstructural stability, extending the useful service temperature of Al alloys to 350°C. However, low ductility and poor fracture toughness levels dictate that stringent controls regarding reinforcement quality and the purity of the matrix alloy, powders and processing are implemented to maximize the alloys’ increased stiffness and strength. This paper compares mechanical behavior through structure-property relationships currently being established for many new aluminum alloys.     

The effect of hot isostatic pressing on crack initiation, fatigue, and mechanical properties of two cast aluminum alloys

This article presents the results of an experimental materials testing program on the effect of hot isostatic pressing (HIP) on the crack initiation, fatigue, and mechanical properties of two cast aluminum alloys: AMS 4220 and 4225. These alloys are often used in castings for high temperature applications. Standard tensile and instrumented Charpy impact tests were performed at room and elevated temperatures. The resulting data quantify improvements in ultimate tensile strength, ductility, and Charpy impact toughness from the HIP process while indicating little change in yield strength for both alloys. In addition standard fracture mechanics fatigue tests along with a set of unique fatigue crack initiation tests were performed on the alloys. Hot isostatic pressing was shown to produce a significant increase in cycles to crack initiation for AMS 4225, while no change was evident in traditional da/dN fatigue crack growth. The data permits comparisons of the two alloys both with and without the HIP process.     

On the possibility of scandium alloying of copper-containing aluminum alloys

Scandium alloying of aluminum alloys can substantially improve their operating properties and weld-ability. Commercially scandium-alloyed alloys have been developed for the Al - Mg, Al - Zn - Mg, and Al - Mg - Li systems. The scandium alloying of aluminum alloys containing copper as an alloying component should be performed carefully, because scandium can produce a chemical compound with copper. This worsens the strength properties of preforms and decreases their plasticity and fracture toughness due to the increased volume fraction of the excess phases. In this work, conditions for scandium alloying are determined for the copper-containing alloys D16 and 1933.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 23 – 27, February, 1995.     

Effect of Yb additions on microstructures and properties of 7A60 aluminum alloy

Al-Zn-Mg-Cu-Zr alloys containing Yb were prepared by cast metallurgy. Effect of 0.30% Yb additions on the microstructure and properties of 7A60 aluminum alloys with T6 and T77 aging treatments was investigated by TEM, optical microscopy, hardness and electric conductivity measurement, tensile test and stress corrosion cracking test. The results show that the Yb additions to high strength Al-Zn-Mg-Cu-Zr aluminum alloys can produce fine coherent dispersoids. Those dispersoids can strongly pin dislocation and subgrain boundaries, which can significantly retard the recrystallization by inhibiting the nucleation of recrystallization and the growth of subgrains and keeping low-angle subgrain boundaries. Yb additions can obviously enhance the resistance to stress corrosion cracking and the fracture toughness property, and mildly increase the strength and ductility with T6 and T77 treatments.     

The influence of chromium on mechanical properties of austempered ductile cast iron

An investigation was carried out to examine the influence of microstructure and chromium on the tensile properties and plane strain fracture toughness of austempered ductile cast iron (ADI). The investigation also examined the growth kinetics of ferrite in these alloys. Compact tension and round cylindrical tensile specimens were prepared from ductile cast iron with Cr as well as without Cr. These specimens were then given four different heat treatments to produce four different microstructures. Tensile tests and fracture toughness tests were carried out as per ASTM standards E-8 and E-399. The crack growth mechanism during fracture toughness tests was also determined. The test results indicate that yield strength, tensile strength, and fracture toughness of ADI increases with an increase in the volume fractions of ferrite, and the fracture toughness reaches a peak when the volume fractions of the ferrite are approximately 60% in these alloys. The Cr addition was found to reduce the fracture toughness of ADI at lower hardness levels (<40 HRC); at higher hardness levels (≥40 HRC), the effect of chromium on the fracture toughness was negligible. The crack growth mechanism was found to be a combination of quasi-cleavage and microvoid coalescences, and the crack trajectories connect the graphite nodules along the way.