AA 7055铝合金时效析出强化模型

利用小角度X射线散射技术获得的系列定量信息,综合运用时效析出动力学理论和析出相切过、绕过强化机制,研究了AA 7055铝合金在120和160℃时效过程中的屈服强度演变模型。结果表明,在时效早期盘状析出相的盘面半径和半厚度均与t^1/2(t为时效时间)成线性关系;在时效后期,析出相尺寸则与t^1/3成线性关系。时效过程中析出相体积分数与t的变化关系遵循JMA (Johnson-Mehl-Avrami)型表达式。综合考虑了GPI区和η’相2类析出相对合金强度的贡献,并且分别考察了这2类析出相的模量强化机制和共格应变强化机制,最终建立了AA 7055铝合金在120和160℃时效过程中的屈服强度变化模型,确定了该合金时效过程中析出相与屈服强度之间的定量关系。     

Enhancing Mechanical Properties of Mg–6Zn Alloy by Deformation-Induced Nanoprecipitation

We presented the solution of deformation-induced precipitation after homogenization to enhance the mechanical properties of Mg–6 Zn alloys. The results show that the improved strategy exhibits more effective strengthening role than grain refinement methods based on low-temperature severe plastic deformation under the same strain. The low-temperature deformation with larger extrusion ratio results in massive nano-sized precipitates and excellent mechanical properties with the yield strength of 355 MPa and the ultimate tensile strength of 405 MPa. The increased mechanical properties are strong and tough enough to resist the stress and not be worn away when the alloy nail penetrates through the pig thigh bone, potentially extending more orthopedic surgery applications for Mg–Zn alloys.     

Modeling of whole process of ageing precipitation and strengthening in Al-Cu-Mg-Ag alloys with high Cu-to-Mg mass ratio

A physically based numerical model to predict the microstructure evolution and yield strength of high Cu-to-Mg mass ratio Al-Cu-Mg-Ag alloys during the whole ageing process was developed.A thermodynamically-based precipitation model,employing the classical nucleation and growth theories,was adapted to deal with the precipitation kinetics (evolution of radius and volume fraction of precipitates for Ω phase) of aged Al-Cu-Mg-Ag alloys.The model gives an estimation of the precipitation kinetics (evolution of radius and density of precipitates for both θ' and Ω phases) of the alloy.The strengthening model based on Orowan mechanism was deduced.The microstructural development and strength predictions of the model are generally in good agreement with the experimental data.     

Sn-Induced Modification of the Precipitation Pathways upon High-Temperature Ageing in an Al-Mg-Si AlloyEI北大核心CSCD

The 6xxx series aluminum alloys (Al-Mg-Si(-Cu) alloys) are widely used for the industrial applications in the lightweight construction, automotive and architecture because of their light weight, medium to high strength, excellent formability and good corrosion resistance. It has been reported that trace Sn addition can accelerate ageing kinetics and increase peak hardness of Al-Mg-Si alloys when ageing at high temperatures (> 210 degrees C). However, the mechanism about it has not been investigated comprehensively yet. For Mg-excess Al-Mg-Si alloys, when aged at 250 degrees C, the alloys are hardened by the beta'-precipitates. While after applying natural ageing prior to artificial ageing, the beta '-precipitates will be formed, with the percentage of which increasing with natural ageing time, and eventually become the main hardening precipitates. In this work, the effect of Sn on natural ageing and subsequent artificial ageing at 250 degrees C in a Mg-rich Al-Mg-Si alloy was investigated by Vickers microhardness measurements and TEM. The results show that adding a small amount (0.2%, mass fraction) of Sn in the Mg-rich Al-Mg-Si alloy can modify the precipitation pathways upon 250 degrees C-ageing: when the alloy is directly artificially aged, the beta '-precipitates are dominant, whereas when the alloy is subjected to " natural ageing+artificial ageing" treatment, upon prolonged natural ageing time, the percentage of beta '-precipitates would not increase but decrease and that of beta'-precipitates would not decrease but increase, but ultimately the beta '-precipitates are still dominant over the beta'-precipitates. The Sn-induced modification of the precipitation pathways can significantly en-hance the age-hardening potential of the alloy upon high-temperature artificial ageing. The addition of Sn increases the effective Si-concentration in the matrix, and consequently changes the precipitation pathways in the Sn-free alloy, which is different from the explanation proposed in literatures.     

高强可焊7A62铝合金的成分设计与跨尺度相强化作用

基于7A62铝合金的成分设计,研究Zn含量和Zn/Mg质量比对Al-Zn-Mg合金强度的影响。采用透射电镜(TEM和HREM)详细地研究7A62铝合金峰值时效的析出相,从多个晶体学方向观察了强化析出相的形貌及其与基体的关系。结果表明:Zn/Mg质量比为2~3、Zn含量增加至6.84%(质量分数)时,7A62合金的强度明显增加。峰值时效后,7A62合金基体形成了体积分数约60%、尺寸小于10 nm的沉淀强化相和体积分数约10%、尺寸为100~200 nm的弥散强化相。基体主要强化析出相是高密度均匀分布的η′相,与基体呈现半共格和晶体取向关系,形成较高晶格错配度;跨尺度位错缠结的弥散强化相是由Al、Zn、Mg、Mn元素组成的平衡相。7A62合金的化学成分和微结构特征使其成为高强可焊的铝合金。     

7A04铝合金时效强化的试验研究及其强度计算

以铝合金时效强化动力学理论为基础,研究了高温预热固溶处理后不同的时效工艺对7A04铝合金组织和性能的影响,得到了优化的双级时效工艺.在此基础上,建立了合金成分、析出相尺寸及其体积分数与合金屈服强度之间的计算模型,并利用该模型对7A04铝合金单级时效和双级时效后的屈服强度进行计算.该模型集成了固溶强化和弥散强化对合金屈服强度的贡献,在达到最大时效强度之前,计算结果和试验测量结果较为一致.此后,随着强化相体积分数计算偏差增加,计算强度与测量强度之间的误差也有所增大.     

Improving the Mechanical Properties of Mg-Gd-Y-Ag-Zr Alloy via Pre-Strain and Two-Stage Ageing

In this study, we investigated the effects of single-stage ageing (SSA), two-stage ageing (TSA), 2% pre-strain + single-stage ageing (P2%SSA) and 2% pre-strain + two-stage ageing (P2%TSA) on the mechanical properties of as-extruded Mg–8Gd–3Y–0.5Ag–0.5Zr alloy (E alloy). Compared with the SSA treatment, the TSA treatment increased the number density of $\beta ^{\prime}$ phase. The P2%SSA and P2%TSA treatments generated the $\gamma ^{\prime}$ phase and chain-like precipitates in addition to the $\beta ^{\prime}$ phase. The contributions of these ageing treatments to the alloy strengthening can be ranked as P2%TSA > P2%SSA > TSA > SSA, because the increments in the tensile yield strength were estimated to be 199 MPa > 148 MPa > 144 MPa > 110 MPa. Different from the traditional strengthening of $\beta ^{\prime}$ phase in the E + SSA and E + TSA alloys, the composite precipitates comprising the $\beta ^{\prime}$ phase, $\gamma ^{\prime}$ phase and chain-like precipitates in the E + P2%SSA and E + P2%TSA alloys provided better combined strengthening effect. The $\beta ^{\prime}$ phase was still dominated in the strengthening effect of the composite precipitates. Owing to the higher number density of $\beta ^{\prime}$ phase in the composite precipitates, the E + P2%TSA alloy exhibited the better mechanical performance as compared with the E + P2%SSA alloy. Finally, the E + P2%TSA alloy had the ultimate tensile strength of 452 MPa, the tensile yield strength of 401 MPa and elongation to failure of 3.3%.     

Microstructure and Mechanical Properties of a Ag Micro-Alloyed Mg-5Sn Alloy

Effects of 1.5 wt.% Ag addition and solid solution?+?artificial ageing at 160 °C on the microstructure and mechanical properties of a Mg-5Sn alloy have been studied. The results show that Ag addition has significantly hardened the solution-treated Mg-5Sn alloy. During the ageing process, the hardness increase rate and the strength and ductility of the Mg-5Sn alloy at each state are also improved by Ag addition. The improved strengthening behavior is primarily attributed to the refinement distribution of the Mg₂Sn precipitates, the enhanced precipitation process, and the synergistic strengthening effect of Mg₂Sn and a metastable plate DO₁₉ phase formed at lower ageing temperature. For each solution-treated alloy, the strength and ductility are higher than the corresponding cast ones. Ageing further enhances the yield strength, and the ductility of the Mg-5Sn-1.5Ag alloy is also increased after ageing. The fracture surfaces of the both peak-aged alloys exhibit the characteristic of a mixture of quasi-cleavage and ductile fracture.     

Effect of large cold deformation after solution treatment on precipitation characteristic and deformation strengthening of 2024 and 7A04 aluminum alloys

1Introduction Studies on thermomechanical treatment of aluminum alloy can date from the1960s[1,2].A great deal of achievements concerning this study has been obtained after near40years of development[3?7].Among them,the achievement of intermediate thermom…     

Strengthening of an Al–Cu–Sn alloy by deformation-resistant precipitate plates

A variation of the Orowan equation is developed for aluminium alloys strengthened by dispersed, deformation-resistant {1 0 0}_α precipitate plates, and the quantitative effects of precipitate volume fraction, number density and aspect ratio on increments in Orowan strengthening are examined. The validity of the model is examined by a combination of mechanical property measurements and rigorous quantitative stereology of the size and distribution of {1 0 0}_α plates of θ′ phase in an Al–4Cu–0.05Sn (wt.%) alloy aged isothermally at 200 °C. For the ageing conditions selected, the predictions of the model for Orowan strengthening increments are in good quantitative agreements with those observed experimentally. The model predicts that, for a given volume fraction and number density of precipitate plates, an increase in plate aspect ratio can lead to a substantial increase in strength. In addition, it is not necessary to invoke a transition from precipitate deformation to Orowan strengthening to account for the form of the precipitation-strengthening response of the alloy. The maximum strengthening increment is associated with the minimum effective inter-particle spacing, rather than a critical thickness of the precipitate plates.     

Double-peak age strengthening of cold-worked 2024 aluminum alloy

The microstructure and mechanical properties of a 2024 Al alloy subjected to different levels of cold-rolling at room temperature and their evolution upon ageing at 453 K were investigated by means of microhardness measurements, tensile tests and transmission electron microscopy. The cold-worked 2024 Al alloy showed double-peak age strengthening behavior. After ageing for 120 min, the samples reached the first peak strength with quite low ductility. However, simultaneous high strength and ductility were achieved by prolonged ageing of 720 min. The first strengthening peak is due to the precipitation of fine S′ precipitates. The optimized mechanical properties of high strength and suitable ductility are attributed mainly to the precipitation of Ω-phase particles at the expense of S′ precipitates after ageing for 720 min. The Ω precipitates are effective in dislocation pinning and accumulation, and they can undergo plastic deformation to some extent, leading to simultaneously improved tensile strength, work-hardening ability and ductility. The present finding sheds light on the development of processing techniques to optimize the mechanical properties of 2024 Al alloy.     

Precipitate characteristics and their effect on the prismatic-slip-dominated deformation behaviour of an Mg–6 Zn alloy

This study provides a detailed quantitative characterization of precipitation in an Mg–6 Zn alloy. Transmission electron microscopy (TEM) was used to characterize the average size, aspect ratio and volume fraction of the rod-shaped precipitates for ageing at 200 °C. The effect of these precipitate characteristics on the prismatic-slip-dominated deformation behaviour of the above alloy has been evaluated. In particular, their effect on the yield strength and work hardening behaviour of the alloy has been determined. The potential role of Zn solute in solution on the rate of dynamic recovery is discussed. TEM was also used to examine the precipitate–dislocation interaction mechanism on the prism plane in various precipitation states. It was found that the Orowan equation is appropriate for predicting the strengthening on the prism and basal planes due to rod-shaped precipitates.     

具有盘状析出相铝合金的时交强化模型

以析出热力学、长大动力学及强化理论为基础,研究了具有盘状析出相的铝合金在时效过程中的析出相尺寸、体积分数变化及其对时效合金强化效果的影响,得到了合金成分、时效参数与组织参数、屈服强度间的解析关系式,进而从微观与宏观相结合的角度建立起了具有盘状析出相铝合金的时效工艺－屈服强度量化模型,并将该模型应用于Al-Cu二元系列合金的时效性能预测,取得了较满意的结果。同时,由数据的归纳和组合得出了Al-Cu二元系列合金中盘状析出相临界形核能垒的简易求解式f（△G,x0/xc）＝常数,有助于该模型的普遍适用化。     

大塑性变形制备超细晶铝锂合金的组织及力学性能研究进展

综述了大塑性变形工艺制备超细晶铝锂合金的显微组织及其力学性能,分析了大塑性变形过程中铝锂合金的组织演变及其影响因素。铝锂合金的强化机制主要是基于析出强化,结合大塑性变形得到的超细晶粒组织可以显著提高强度和塑性,并得到优异的超塑性。表明大塑性变形加工铝锂合金,尤其是等通道挤压制备的超细晶铝镁锂合金在超塑性工业具有广阔的发展前景。     

结构钢中含铜析出相的时效强化作用

观察并研究了高纯Fe-1．03wt％Cu和Fe-1．65wt％Cu合金中含铜粒子的时效析出对屈服强度的影响、析出粒子尺寸的分布、以及析出粒子对位错运动的阻碍作用。用Frank-Read强化理论分析了析出粒子与屈服强度的定量关系。结果表明，析出粒子是含有一定铁的亚稳Cu-Fe相，且具有一定的塑性变形能力，从而使得含铜钢能在高强度的前提下仍具有高塑性的特征。含铜析出粒子不是刚性粒子，因而其强化效应低于传统的刚性化合物析出粒子。但析出粒子中含较多的铁，可促使粒子体积量明显增多，因此仍能实现很高的整体强化效应。增加析出粒子中的铜含量可以提高粒子对位错运动的阻力及与之相应的屈服强度。     

A unified constitutive model for multiphase precipitation and multi-stage creep ageing behavior of Al-Li-S4 alloy

A unified constitutive model is presented to predict the recently observed “multi-stage” creep behavior of Al-Li-S4 alloy. The corresponding microstructural variables related to the yield strength and creep deformation of the alloy during the creep ageing process, including dislocations and multiple precipitates, have been characterized in detail by X-ray diffraction (XRD) and transmission electron microscopy (TEM). For the yield strength, the model considers the multiphase strengthening behavior of the alloy based on strengthening mechanisms, which includes shearable T₁ precipitate strengthening, non-shearable T₁ precipitate strengthening and θ′ precipitate strengthening. Based on creep deformation mechanism, the “multi-stage” creep behavior of the alloy is predicted by introducing the effects of interacting microstructural variables, including the radius of multiple precipitates, dislocation density and solute concentration, into the creep stress-strain model. It is concluded that the results calculated by the model are in a good agreement with the experimental data, which validates the proposed model.     

Ce含量对Mg-Li-Al-Zn合金显微组织和拉伸性能的影响(英文)

制备了Mg-5Li-3Al-2Zn-xCe(x=0-2.5;质量分数,%)铸态合金,并将所得合金分别于300°C和370°C进行均匀化和固溶处理;研究固溶处理后合金显微组织和拉伸性能的变化。结果表明,合金中加入Ce后出现Al2Ce/Al3Ce析出相,此时合金主要由α-Mg、Al2Ce、Al3Ce和AlLi相组成;固溶处理后合金中AlLi和Al-Ce析出相数量减少。析出相的数量与形态对合金的力学性能十分重要,含有1.0%Ce的合金获得了优良的拉伸性能。固溶处理后Mg-5Li-3Al-2Zn-0.5Ce合金的强度和伸长率都得到了大幅度的提高,这是因为合金在固溶处理后由于基体中的溶质原子增加而获得良好的固溶强化作用。     

Determining the effect of microstructure and heat treatment on the mechanical strengthening behavior of an aluminum alloy containing lithium precipitation hardened with the δ′ Al3Li intermetallic phase

The effect of the thermal treatment and composition on microstructure and subsequent mechanical behavior of an Al-2.6 wt.% Li-0.09 wt.% Zr alloy that was solution heat treated (SHT) and artificially aged for a series of aging times and temperatures was studied. The underaged, peakaged, and overaged thermal heat treatments were studied to determine the effect of the microstructure and processing on the mechanical properties. The precipitates in the microstructure, which impede dislocation motion and control the precipitation strengthening response as a function of aging practice, were analyzed as the basis for controlling the strengthening depending on their size distribution, average size, and interparticle spacing. The average particle size, spacing, and size distribution were determined from the microstructure as a function of the thermal processing and composition. For the demonstration alloy, the primary strengthening was a direct consequence of ordered coherent Al₃Li (δ′) intermetallic precipitates, which are uniformly distributed throughout the microstructure and restrict the glide motion of dislocations during plastic deformation. The Al₃Li average particle size, distribution, spacing, and volume fraction are closely related to the overall mechanical behavior and are a result of the heat treating practice and composition. Consequently, a micromechanical model was developed for predicting the precipitation hardening response in terms of the variation in polycrystalline strength with aging time, aging temperature, and composition. The overall micromechanical model, which was determined from the particle coarsening kinetics, dislocation mechanics, thermodynamics, resolved shear stress, as well as the dislocation particle shearing and bypassing mechanisms, accurately predicted the mechanical strength in the underaged, peak-aged, and overaged tempers of the demonstration alloy.     

Effect of pre-deformation on aging characteristics and mechanical properties of Mg-Gd-Nd-Zr alloy

The effect of plastic deformation prior to artificial aging on the aging characteristics and mechanical properties of a Mg-I lGd-2Nd-0.5Zr （mass fraction, %） alloy was investigated. After solution treatment at 525 ℃ for 4 h, the alloy was subjected to cold stretching deformation of 0%, 5% and 10%, respectively. The as-deformed specimens possess high density of dislocations and mechanical twins, which increase with elevated deformation. As compared with non-stretched alloy, the stretched alloy shows accelerated age-hardening response and slightly enhanced peak hardness when aged at 200 ℃. Comparison of the microstructures in undeformed and deformed specimens after 200 ℃, 24 h aging reveals that pre-deformation induces the heterogeneous nucleation of precipitations at dislocations and twin boundaries in addition to the homogeneous precipitation in the matrix. Room and high temperature tensile test results show that pre-deformation enhances the strength of the alloy, especially at room temperature, though the ductility declines. The improvement in strength of deformed and aged alloy is attributed to the combined strengthening effect of precipitates, deformation structures and grain boundaries.     

Effect of Zn Addition on the Microstructure and Mechanical Properties of Cast Mg-10Gd-3.5Er-xZn-0.5Zr Alloys

In this work, the effects of Zn content (0-2 wt%) on microstructural evolution and mechanical properties of cast Mg-10Gd-3.5Er-0.5Zr alloys are studied. The results show that the as-cast Mg-10Gd-3.5Er-xZn-0.5Zr alloys are mainly composed of Mg matrix and secondary (Mg, Zn)₃(Gd, Er) phases distributed along grain boundaries. With the increase in Zn content, the volume fraction of secondary (Mg, Zn)₃(Gd, Er) phases increases and the grains get refined. In the process of solid solution treatment, Zn addition can lead to the formation of long-period stacking ordered (LPSO) structures and the volume fraction of LPSO structures increases with Zn content. In addition, the Zn addition can reduce the vacancy formation energy and accelerate the diffusion rate of RE elements in Mg matrix. Because of the comprehensive effect of secondary phases and the accelerated diffusion rate, the base alloy and 2Zn alloy have less grain growth after solid solution treatment than that of the 0.5Zn alloy and 1Zn alloy. The precipitation process is also accelerated by enhanced diffusion rate. At room temperature (RT), the strengthening effect of β^'+ β₁ precipitates is more effective than that of LPSO structures, so the peak-aged 0.5Zn alloy exhibits the most excellent mechanical performance at RT, with yield strength of 219 MPa, ultimate tensile strength 296 MPa and elongation of 6.4%. While LPSO structures have stronger strengthening effect at elevated temperature than that of β^'+ β₁ precipitates, so the 1Zn alloy and 2Zn alloy have more stable mechanical performance than that of the base alloy and 0.5Zn alloy with the increase in tensile temperature.