Effects of Ag on microstructure and mechanical properties of 2519 aluminum alloy

The effects of Ag on the microstructure and mechanical properties of 2519 aluminum alloy were investigated by means of tensile test, micro-hardness test, transmission electron microscope and scanning electron microscope. The results show that the addition of 0.3 % （mass fraction） Ag accelerates 2519 aluminum alloy＇s age-hardening, increases its peak hardness and reduces 4 h of peak aged time at 180 ℃. The addition of 0. 3% （mass fraction） Ag increses the tensile strength at room temperature and elevated temperature. This increment at room temperature and 200 ℃ is 24 MPa and 78 MPa, respectively. In contrast, the elongation of 2519 aluminum alloy is decreased with Ag addition. The increase of tensile strength of 2519 aluminum alloy with Ag addition is attributed to the high volume fraction of Ω phase.     

Effect of heat treatments on tensile properties and microstructure of 2195 alloy

Effect of various aging treatments on the tensile properties and microstructure of 2195 alloy has been investigated. The experimental results show that promising combination of strength and ductility is achievable under T₈ temper. The lower aging temperature reduces T₁ precipitation on the subgrain or grain boundaries and favors uniform dispersion of T₁ phases in the matrix, resulting in better strength and ductility. Prior deformation before aging has improved tensile strength with a slight decrease in ductility. Pre-aging after prior deformation had little effect on the age-hardening behavior of 2195 alloy. Project supported by the Key Program of the 9th Five-year Plan of China Synopsis of the first author Zheng Ziqiao, professor, born in 1944, major research fields: physical metallurgy of aluminum alloys; functionally gradient materials; self-propagation high temperature synthesis.     

GH4169合金δ相的析出动力学研究

采用X射线衍射技术测定了GH4169合金中δ相在900℃、930℃时的析出动力学,并采用光学显微镜进行组织观察,结果表明：δ相的形核位置和形核方式与时效温度有关.当时效温度在900℃时,δ相主要在晶界和孪晶界上形核析出,而晶内颗粒状δ相由时效初期析出的亚稳态γ″相转变形成;当时效温度为930℃时,δ相不仅可以在晶界和孪晶界形核析出,还可以从基体γ莫直接形核析出,并且随着时效时间的延长,δ相逐渐向晶内生长,最终形成魏氏体δ相.当时效温度一定时,δ相的析出含量与时效时间满足Avram i方程.     

动态时效对Al-Cu-Mg-Ag合金组织与力学性能的影响

对Al-Cu-Mg-Ag新型耐热铝合金进行预时效+中温轧制变形+终时效的动态时效工艺处理,采用硬度测试、拉伸性能测试,结合金相显微组织分析和透射电子显微分析,探究动态时效对其力学性能与微观组织的影响。结果表明：动态时效能够提高合金的时效硬化速率,随着变形量的增大,合金的峰时效时间逐渐减小,峰值硬度逐渐增大。动态时效能够改变晶粒形貌,随着变形量的增大,晶粒的纵横比增大,位错数量增多,强化相数量增多尺寸减小,使得合金强度随着变形量的增大而逐渐增大,但伸长率逐渐减小。变形量为50%合金的强度最高,抗拉强度和屈服强度最大,分别为527.4 MPa和467.0 MPa,伸长率保持在较高值9.1%。     

热处理对反向挤压AZ80镁合金组织与性能的影响

采用光学和扫描电子显微观察、X射线衍射及拉伸试验研究了反向挤压AZ80镁合金不同热处理状态下的显微组织及性能．结果表明：反向挤压AZ80镁合金热处理后析出的β－Mg17Al12相（β相）在不同热处理状态下形貌不同．经T6热处理后,口相在晶界处呈层片状析出,与挤压态相比,合金的强度稍有降低,但延伸率明显提高;经T5热处理后,卢相在晶界处仍呈层片状,而在晶内呈颗粒状,与挤压态相比,合金的强度明显提高,但延伸率降低．     

Microstructure and RRA treatment of LFEC 7075 aluminum alloy extruded bars

The microstructures after casting and extruding, the mechanical properties and electrical conductivity after RRA treatment of conventional DC casting and low frequency electromagnetic casting (LFEC) 7075 aluminum alloy were investigated. The results showed that finer grains which distributed more homogeneously was obtained in LFEC ingots compared with those conventional DC ingots. The extruded bars of LFEC alloy kept its fine grain features of original as-cast structure. In the RRA treatment, with the extension of second aging time, the tensile strength and hardness of alloy decreased, but the electrical conductivity increased. Meanwhile, as the second aging temperature raised, the phase change rate in precipitation also increased. Under the same conditions, extruded bars of LFEC alloy had better performance than that of conventional DC cast alloy. The optimum RRA heat treatment process was 120 ℃/24 h+180 ℃/30 min+120 ℃/24 h. The LFEC extruded bars acquired tensile strength 676.64 MPa, hardness 198.18, and electrical conductivity 35.7% IACS respectively, which were higher than that in the T6 temper, indicating that a notable RRA response takes place in LFEC extruded bars, whose second-step retrogression time was 30 min, and it was suitable for mass production.     

时效态Al-Zn-Mg-Cu-Zr-Sc合金的组织与疲劳性能

为了研究时效处理对Al-7.2Zn-2.5Mg-1.5Cu-0.08Zr-0.12Sc合金的组织与疲劳性能的影响,利用透射电子显微镜对合金的显微组织进行了观察分析,并针对不同时效状态的合金进行了低周疲劳实验.结果表明,经过150℃×6 h时效处理后,合金晶内析出相较少,晶界无析出相;经过150℃×36 h时效处理后,合金晶内析出相较为细小,并呈弥散分布,同时晶界析出断续分布的平衡相,并存在晶界无析出带;经过150℃×48 h时效处理后,合金的析出相均已长大,且晶界无析出带发生宽化.经过150℃×36 h时效处理后的合金,表现出了较高的循环变形抗力与较长的低周疲劳寿命;不同时效状态合金的塑性应变幅、弹性应变幅与载荷反向周次之间,以及循环应力幅与塑性应变幅之间均呈线性关系.     

Effect of low temperature thermo-mechanical treatment on microstructures and mechanical properties of TC4 alloy

The effects of low temperature thermo-mechanical treatment (LTTMT) on microstructures and mechanical properties of Ti-6Al-4V (TC4) alloy were studied by optical microscopy (OM), tensile test, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results confirm that the strength of TC4 alloy can be improved obviously by LTTMT processing, which combines strain strengthening with aging strengthening. The effect of LTTMT on the alloy depends on the microstructure of the refined and dispersed α+β phase on the basis of high dislocation density by pre-deformation below recrystallization temperature. The tensile strength decreases with the increase of pre-deformation reduction. The optimal processing parameters of LTTMT for TC4 alloy are as follows:solution treatment at 900 ℃ for 15 min, pre-deformation in the range of 600-700 ℃ with a reduction of 35%, finally aging at 540 ℃ for 4 h followed by air-cooling.     

Effects of Aging Treatment on Intergranular Corrosion and Stress Corrosion Cracking Behavior of AA7003

In order to study the effects of aging treatment on the intergranular corrosion(IGC) and stress corrosion cracking(SCC) of 7003 aluminum alloy(AA7003), the intergranular corrosion test, electrochemical test and slow strain rate test(SSRT), combined with optical microscopy(OM) and scanning electron microscopy(SEM) as well as transmission electron microscopy(TEM) observations have been carried out. The IGC and electrochemical test results showed that the IGC resistance of AA7003 for peak aged(PA) temper is the lowest, with double peak aged(DPA) the moderate, and retrogression and re-aging(RRA) the highest among three tempers, which is attributed to the continuous feature of precipitation on grain boundary of PA temper and the interrupted feature of precipitation on grain boundary of DPA and RRA tempers, as well as the wide precipitation free zones(PFZ) of RRA temper. In addition, the SSRT results indicated that all three tempers AA7003 are susceptible to SCC in IGC solution, and the change tendency of SCC susceptibility(ISCC) of AA7003 for three tempers follows the order: ISCC(RRA)ISCC(DPA)ISCC(PA).     

Grain boundary characteristics and tensile properties of Ti14 alloy after semi-solid deformation

The microsuucture and room-temperature tensile properties of Til4,a new α+Ti2Cu alloy,were investigated after conventional forging at 950℃ and semi-solid forging at 1000 and 1050℃,respectively.Results show that coarse grains and grain boundaries are obtained in the semi-solid alloys.The coarse grain boundaries are attributed to Ti2Cu phase precipitations occurred on the grain boundaries during the solidification.It is found that more Ti2Cu phase precipitates on the grain boundaries at a higher semi-solid forging temperature,which forms precipitated zones and coarsens the grain boundaries.Tensile tests exhibit high strength and low ductility for the semi-solid forged alloys,especially after forging at 1000℃.Fracture analysis reveals the evidence of ductile failure mechanisms for the conventional forged alloy and cleavage fiacture mechanisms for the alloy after semi-solid forging at 1050℃.     

The Effects of Aging Precipitation on the Recrystallization of CuNiSiCr Alloy

The interaction between precipitation and recrystallization and its effect on the properties of the Cu-Ni-Si-Cr alloy during aging were discussed. The results show that the deformation results in much more dispersed precipitation of the phases. The precipitations have accelerating or retarding effects on the recrys allization. On the formation and growth of recrystallization, the precipitated phases are coarsed or dissolved in front of grain boundaries following a re-precipitation in the recrystallization area.     

Influence of quench transfer time on microstructure and mechanical properties of 7055 aluminum alloy

The influence of quench transfer time on the microstructure and mechanical properties of 7055 aluminum alloy with and without zirconium was investigated by tensile properties test, optical microscopy, scanning electron microscopy and transmission electron microscopy. For the Zr-free alloy, the strength increases to the highest value at 20 s with transfer time, and then decreases slightly. The elongation decreases slowly with transfer time within 20 s, and more rapidly after 20 s. For the Zr-containing alloy, prolonging transfer time within 20 s results in slight decrease in the strength and elongation, and rapid drop of which is observed after 20 s. For the Zr-free alloy, prolonging transfer time can increase the percentage ofintergranular fracture, which is mainly caused by wide grain boundary precipitate free zone. The failure mode of the Zr-containing alloy is modified from the predominant transgranular void growth and intergranular fracture to transgranular shear and intergranular fracture with increase in the transfer time, which is attributed to the wider grain boundary precipitate free zone and coarse equilibrium η phases in the matrix.     

Localized Corrosion and Stress Corrosion Cracking Behavior of AA7003 in a 3.5 wt% NaCl Aqueous Solution

The microstructure,localized corrosion (LC) and stress corrosion cracking (SCC) behavior of 7003 aluminum alloy (AA7003) under various aging treatments (peak aging (PA),double peak aging (DPA),regression and re-aging (RRA)) were investigated by means of transmission electron microscope (TEM),scanning electron microscopy (SEM),electrochemical impendence spectroscopy (EIS) and slow strain rate tensile test.The results of TEM showed a discontinuous distribution of grain boundary precipitates of AA7003 under DPA and RRA treatments,which is beneficial for increasing the resistance of LC and SCC.Meanwhile,LC was found initiating firstly on intermetallics which caused the dissolution of surrounding matrix,then pitting holes were formed and developed into matrix.In addition,the SCC process of AA7003 could be divided into two stages,i e,initial pre-cracking and breeding cracking.The EIS analysis,cross-section morphologies and fracture surfaces of specimens indicated that DPA and RRA treatments significantly decreased the crack growth rate during breeding cracking stage,especially for RRA treatment.     

热挤压镁合金AZ91的微观组织及其力学行为

研究了热挤压镁合金AZ91的微观组织以及在不同试验温度和不同的热处理条件下的拉伸力学性能.结果表明：热挤压可以显著减小AZ91合金的晶粒尺寸，其拉伸力学性能与试验温度密切相关；可以通过热处理来改善其拉伸力学性能，其中人工时效及固溶时效工艺均是改善和提高挤压后AZ91镁合金力学性能的有效途径.此外，利用扫描电镜分析了AZ91镁合金拉伸试样的断口形貌，并探讨了其拉伸断裂机制.     

时效对Mg-7Gd-4Y-0.6Zn-0.6Zr合金显微组织及硬度的影响

为了提高Mg合金的强韧性和抗高温性能.文中通过显微硬度测试、差示扫描量热仪及透射电镜分析,研究了挤压Mg-7Gd-4Y-0.6Zn-0.6Zr系镁合金的显微硬度及时效析出相的结构.结果表明:钆的添加增强了Mg-Gd-Y合金的时效硬化效果,对合金时效硬化的总体规律无明显影响.透射电镜分析发现具有DO19超点阵的β″和斜方晶体β′相在合金时效硬化阶段析出,提高了合金硬度.在时效后期由于粗大的针片状1β相析出,使合金硬度下降.     

改型GH4133A合金长期时效的组织稳定性研究

采用显微组织观察和图像分析等方法,研究了改型GH4133A合金在650,700和750℃下长期时效过程中的组织变化.结果表明：在650℃和700℃下时效过程中,合金的组织变化规律一致,组织具有良好的稳定性.而在750℃时效时,500 h后开始出现η相.随时效时间增长,η相进一步析出、变长和粗化,由晶界向晶内生长;γ′相和M23C6数量增加;MC型碳化物则减少.     

Mg-Y4-Nd3合金的組織與摩擦磨損性能

研究了Mg-Y4-Nd3合金鑄態和T6處理(525℃固溶處理8 h,250℃時效處理16 h)后的顯微組織、力學性能和摩擦磨損性能。結果表明:鑄造Mg-Y4-Nd3合金共晶相分布在α-Mg固溶體晶界上,呈不連續網狀分布。經過固溶時效處理后,合金為等軸晶組織,共晶相基本固溶到-αMg基體中,時效析出沉淀相呈彌散分布。兩種處理合金的抗拉強度都隨溫度的升高而降低,伸長率均隨溫度的升高而升高,同溫度下,T6處理的合金抗拉強度高于鑄態合金。T6處理的合金在干滑動摩擦條件下,隨著載荷的增加,摩擦系數降低,磨損量增加,磨損機制由磨粒磨損伴有氧化磨損向剝層磨損過渡,在高載荷下磨損表面出現塑性變形擠出現象。     

Retrogression characteristics of a novel Al-Cu-Li-X alloy

Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The retrogression treatments of aging at 155°C for 12 h followed by aging at 220 and 240°C were chosen by determining the peak temperature of δ' precipitation at 230°C by DSC. The retrogression treatment at a lower temperature of 220°C causes the precipitation and coarsening of δ' and θ' phases in the matrix, resulting in an ...     

含稀土Er的Al-Zn-Mg合金的组织与性能

为了探讨稀土Er对热处理可强化(沉淀强化)的铝合金系作用,采用铸锭冶金法制备了6种含Er量不同的Al-Zn-Mg合金进行了深入分析.通过硬度测试、拉伸力学性能测试、金相观察、X射线衍射和扫描电镜观察,研究了稀土元素Er对Al-Zn-Mg合金显微组织和力学性能的影响.实验结果表明,稀土元素Er可以显著地细化Al-Zn-Mg合金的铸态晶粒,减小其枝晶网胞,当Er的添加量达到w(Er)=0.7％时,枝晶网胞几乎完全消失,晶粒变得非常细小且分布均匀;对于合金的冷轧态组织以及时效态晶粒也有同样的细化效果;添加Er后,Al-Zn-Mg合金在冷轧态及时效态下的屈服强度(σ0.2)及抗拉强度(σh)都得到了显著的提高,但塑性有所降低;稀土元素Er添加到Al-Zn-Mg合金中,主要与Al相互作用形成了Al3Er相.合金显微组织的细化及合金的强化都与该相的形成和析出有关.     

Grain-scale Stress and GND Density Distributions around Slip Traces and Phase Boundaries in a Titanium Alloy

For TA15 titanium alloy, slip is the dominant plastic deformation mechanism because of relatively high Al content. In order to reveal the grain-scale stress field and geometrically necessary dislocation(GND) density distribution around the slip traces and phase boundaries where the slip lines are blocked due to Burgers orientation relationship(OR) missing. We experimentally investigated tensile deformation on TA15 titanium alloy up to 2.0% strain at room temperature. The slip traces were observed and identified using high resolution scanning electron microscopy(SEM) and electron backscatter diffraction(EBSD) measurements. The grain-scale stress fields around the slip traces and phase boundaries were calculated by the cross-correlationbased method. Based on strain gradient theories, the density of GND was calculated and analyzed. The results indicate that the grain-scale stress is significantly concentrated at phase/grain boundaries and slip traces. Although there is an obvious GND accumulation in the vicinity of phase and subgrain boundaries, no GND density accumulation appears near the slip traces.