Precipitation behavior and properties of a new high strength Al-Zn-Mg-Cu alloy

The microstructure and the associated hardness, strength and electrical conductivity of a new Al-Zn-Mg-Cu alloy during one-step ageing treatment were systematically studied. The results show that the electrical conductivity of the alloy increased continuously with increasing ageing temperature and ageing time. At the early stage of ageing, the hardness and strength of the alloy increased rapidly and then reached the peak value. When aged at 120 °C, the hardness and strength maintained at high level for a long time after the peak value. The main precipitations are GPI zones, GPII zones and metastable η′ phase. GPI and GPII zones are found in the alloy after ageing for 24 h at 120 °C, which indicates that some stable GP zones can exist through the ageing process. When aged at 160 °C, the hardness and strength decreased rapidly after the peak value. The precipitation process is significantly promoted compared with that aged at 120 °C. Both GPI zones and GPII zones disappeared after ageing for 1 h at 160 °C. The main precipitates are η′ phase when aged at 160 °C for 1 h. The main precipitates are η phase when the ageing time prolongs to 24 h.

Strength and structure variation of 2195 Al-Li alloy caused by different deformation processes of hot extrusion and cold-rolling

2195 Al-Li alloy was deformed through extrusion followed by cold-rolling.The textures of the extruded plate and cold-rolled sheet after solutionization were investigated.The longitudinal strength and precipitates after T8 aging were measured and observed,respectively.Compared to those in the sheet,T1(Al2 Cu Li)precipitates in the extruded plate after T8 aging are non-uniform,and their incubation time is shorter.The extruded plate after solutionization is not recrystallized and contains 55.28%deformation textures of Brass and S.In the cold-rolled sheet after solutionization,massive recrystallization occurs and S component disappears.Due to the higher fraction of Brass and S textures with higher Schmid factor and lower equivalent sliding system number,the extruded plate possesses an yield strength not higher or even lower,but a tensile strength higher,than the cold-rolled sheet after solutionization.In addition,during the aging after pre-stretch,these textures promote T1 precipitation on preferred sliding planes of cold-rolled sheet and cause its higher yield strength and tensile strength after T8 aging.

Effects of pre-deformation on microstructure and properties of Al–Cu–Mg–Ag heat-resistant alloy

The effects of the pre-deformation on the microstructure, mechanical properties and corrosion resistance of Al–Cu–Mg–Ag alloys were investigated by means of hardness tests, tensile tests, intergranullar corrosion (IGC) tests and transmission electron microscopy (TEM), respectively. The results show that with the increase of deformation amount, the aging hardening rate increases while the strength of the alloy decreases and then increases. The sample with a pre-deformation of 6% possesses the highest tensile strength due to the refinedly and homogeneously distributed precipitations. The pre-deformation aging accelerates the heterogeneous nucleation of Ω and θ′ phases at dislocations, and also refines the precipitations both in the grains and along the grain boundaries. The precipitation of Ω phase is restrained while that of θ′ phase is accelerated in pre-deformed Al–Cu–Mg–Ag alloy compared with the sample without pre-deformation. In addition, the width of the precipitate free zone decreases with increasing the pre-deformation amount, leading to a narrower IGC passageway. This results in an enhanced IGC resistance of Al–Cu–Mg–Ag alloy treated by pre-deformation aging. © 2017, Central South University Press and Springer-Verlag GmbH Germany.

Microstructure and mechanical properties of Mg,Ag and Zn multi-microalloyed Al-(3.2-3.8)Cu-(1.0-1.4)Li alloys

To develop super-high strength Al-Li alloy,the microstructures and mechanical properties of Mg,Ag and Zn microalloyed Al-（3.2-3.8）Cu-（1.0-1.4）Li alloys（mass fraction） with T8 temper were studied.The results showed that 1%of lower Li content restricted the strengthening effect of increasing Cu content,while simultaneous increase in Cu and Li contents contributed effectively to the enhancement of strength.The alloys were mainly strengthened by plenty of fine and well dispersed TI（Al2CuLi）precipitates.There were also some minor precipitates of θ＇（Al2Cu） and δ＇（Al3Li）,which became less in number density,even disappeared during the aging process.Meanwhile,higher Li content favored the formation θ＇ and δ＇ and a small amount of S＂（Al2CuMg） phases.In addition,strengthening effect and microstructure variation were analyzed through total non-solution mole fraction of Cu and Li and their mole ratio.To obtain Al-Li alloy with super-high strength,the total mole fractions of Cu and Li should be increased,and their mole ratios should also be kept at a certain high level.

Microstructure and properties of Cu-Ni-Si-Zr alloy after thermomechanical treatments

The effect of thermomechanical treatments on the microstructures and properties of Cu-2.1Ni-0.5Si- 0.2Zr alloy was investigated. The hot-rolled plates were solution treated at 920 ℃ for 1.5 h, quenched into water, cold rolled by 70 % reduction in thickness, and then aged at 400, 450 and 500 ℃for various times. The variation in tensile strength and electrical conductivity of the alloy was measured as a function of the aging time. The results show the peak strength value of 665 MPa for the alloy aged at 450 ℃ for 2 h. However, the electrical conductivity is observed to reach a maximum of 47 % IACS aged at 450℃for 8 h. OM, SEM, and TEM were used for microstructural inspection of the alloy. Precipitation occurs preferentially at deformation bands in the cold-rolled alloy. Properties behavior is discussed in the light of microstructural features.

High strength Al-Cu-Mg based alloy with synchronous improved tensile properties and hot-cracking resistance suitable for laser powder b e d fusion

In present work,a novel crack-free Al-Cu-Mg-Si-Ti alloy with synchronous improved tensile properties and hot-cracking resistance was proposed and successfully manufactured by laser powder bed fusion(LPBF).The microstructure evolution behaviors and the corresponding strengthening mechanisms were investigated in detail.The LPBF-processed Al-Cu-Mg-Si-Ti alloy presents a heterogeneous microstructure consisting of ultrafine equiaxed grains(UFGs)at the boundary and coarse columnar grains(CGs)at the center of the single molten pool.Pre-precipitated D022-Al 3 Ti particles were found to act as the nuclei to refine the grains at the boundary of the molten pool during solidification process,which is attributed to the low cooling rate providing the sufficient incubation time for the precipitation of D022-Al 3 Ti.There are two orientation relationships(ORs)betweenα-Al and D022-Al 3 Ti,i.e.[001]α-Al//[001]D022-Al3Ti,(200)α-Al//(200)D022-Al3Ti and[1¯1¯2]α-Al//[¯111]D022-Al3Ti,(1¯11)α-Al//(¯11¯2)D022-Al3Ti,which are two of the eight ORs predicted with the E2EM model.Refined grains in present alloy,no matter for UFGs or CG,exhibited high critical hot-cracking stress,which means a strong hot-cracking resistance.Dual-nanoprecipitation of Cu-,Mg-,and Si-rich Q’and S’phases was introduced to enhance the mechanical performance ofα-Al matrix.The as-built sample exhibits superior tensile properties,with the yield strength(YS)of 473±8 MPa,ultimate tensile strength(UTS)of 541±2 MPa and elongation(EI)of 10.9%±1.2%.

高强β钛合金的发展现状与强化方法

钛合金是比强度最高的金属材料之一,广泛应用在航空航天领域。随着材料技术的进步,人们对高强钛合金的研究与开发也逐渐深入。综述了国内外高强β钛合金的发展现状与主要的强化方式。重点介绍了Ti-13-11-3、Ti-l023、Ti-5553以及Ti-55531等典型高强钛β合金。梳理了高强β钛合金的设计思路,指出了限制高强β钛合金向更优性能发展的瓶颈并提出了可能的解决途径。总结了固溶强化、析出强化、加工硬化、细晶强化以及增材技术等高强β钛合金的强化方法,以期为进一步提高高强β钛合金的强度、优化高强β钛合金综合性能提供指导。

轧制温度对7075铝合金组织演变及力学性能影响

铝合金作为非钢质结构材料,在地质勘探、石油开采和科学钻探等领域的深井钻探中得到广泛应用。随着大陆及海洋深部油气钻探需求日益增加,对钻探装备和工具的综合性能提出了更高的要求。高强度铝合金以高比强度、低刚度和高耐腐蚀性能等显著优点,已在大位移井、定向井和超深井钻探中得到广泛应用。然而,目前对钻杆用7075超硬铝合金的热加工性能缺乏系统研究。为解决该问题,对7075铝合金在不同轧制温度下的组织演变和力学性能进行了系统地分析和研究。通过光学显微镜和X射线对合金晶粒尺寸和第二相的分布情况进行了观察分析,利用万能试验机对合金的抗拉强度和断裂延伸率等力学性能进行了研究。结果表明,随着轧制温度的升高,7075铝合金的组织和力学性能均会发生显著变化。在轧制温度250—350℃范围内,7075铝合金晶粒尺寸先增大后减小,晶粒当量直径平均值从215 μm增加至257 μm,后又减小至220 μm;当轧制温度为400℃时,合金的晶界组织不明显,原始粗大晶界逐步消失,出现了细小球状晶粒且当量直径平均值减小至47 μm。抗拉强度结果表明,随着轧制加工温度从250℃升高到400℃时,7075铝合金的抗拉强度变化的趋势为先减小后增大。当轧制温度为350℃时抗拉强度达到最低值521 MPa,当轧制温度为400℃时抗拉强度达到最大值570 MPa。此外,高的轧制温度(400℃)能显著增强7075铝合金的强度和塑性。拉伸断口的SEM图像显示,轧制温度400℃时,7075铝合金样品的断裂方式从偏脆性断裂变为偏韧性断裂。因此,轧制温度400℃被认为是7075铝合金适宜的热轧加工温度。本研究为不同轧制温度对轻质高强7075铝合金的力学性能影响规律提供了理论支撑。

Cu、Li含量对Mg、Ag、Zn复合微合金化铝锂合金力学性能及微观组织的影响

通过18个不同Cu（3.24%~4.16%）、Li（0.94%~1.44%）含量的0.4Mg＋0.4Ag＋0.4Zn复合微合金化Al-Cu-Li合金,研究总结了T8时效处理时Cu含量及Li含量对铝锂合金强度和微观组织的影响,并采用合金中非固溶Cu、Li原子总分数及Cu/Li原子分数比例阐明了强度及微观组织的影响规律及机理。结果表明：合金中时效强化相包括T1相（Al2Cu Li）、θ＇相（Al2Cu）和δ＇相（Al3Li）。Cu、Li原子总分数及其比例增加,合金中时效强化相总量及T1相比例大,合金强度较高。而Cu/Li原子分数比例较低,δ＇相比例增加,T1相比例下降,合金强度降低。

Mg-6Gd-Y-0.6Zr的析出行为和力学性能

利用光学显微镜、扫描电镜、X线衍射、透射电镜等手段研究添加1%Y(质量分数,下同)对Mg-6Gd-0.6Zr合金析出行为和力学性能的影响。研究结果表明:添加合金元素Y能大大促进Mg-6Gd合金的时效析出;具有高过饱和度的Mg-6Gd-Y-0.6Zr合金在200℃表现出显著的时效硬化现象;随着时效温度的升高,晶界周围析出相极度粗化并且β′相体积分数降低、分布不均;尤其在250℃峰时效的组织中观察到Mg-6Gd合金所不具备的β′相。200℃时效72 h后,合金获得优异的力学性能,其室温抗拉强度、屈服强度和伸长率分别为354 MPa,292 MPa和9.5%,250℃时抗拉强度、屈服强度和伸长率分别为307 MPa,220 MPa和13.6%。

焊接速度对高强铝合金搅拌摩擦焊接头组织及力学性能的影响

焊接速度对搅拌摩擦焊接头内焊核区、热机影响区和热影响区组织和晶界沉淀相均有较大的影响。随着焊接速度的提高 ,焊核区和热影响区内的晶粒尺寸和沉淀颗粒大小、分布密度变化均较大 ;热机影响区内组织的变形程度变化明显。组织和力学性能综合分析表明 ,控制焊接速度 ,获得优良的焊核区组织有利于提高接头的力学性能。性能测试结果表明 ,焊接速度v =37.5mm/min时 ,2A12CZ铝合金接头强度达到最大值 (331MPa)。

铜基合金沉淀硬化研究

采用感应熔炼制备了铜基合金Cu 2 0Mg 1 5Ag(质量百分数 ,下同 ) ,并通过滚压和热处理进一步使合金的成分均一化。样品分别在 4 5 0℃和 5 0 0℃下进行不同时间的时效处理 ,然后测定其维氏硬度随时效时间的变化规律。扫描电镜显微分析揭示了合金显微组织结构的演变 ,且表明 ,时效处理后第二相Cu2 Mg沉淀颗粒非常细小 ,并很好地分散于铜基体中。沉淀硬化实现了铜基合金的高效强化 ,最佳的时效条件为 4 5 0℃× 96h。

热处理对Al-6Zn-2Mg-2Cu合金晶间腐蚀行为的影响

采用显微分析技术和统计分析方法研究了Al-6Zn-2Mg-2Cu合金经固溶+T6或T76时效处理后的显微组织和在腐蚀环境下的晶间腐蚀行为及腐蚀深度的动力学。结果表明:T76时效后,第二相细小弥散分布在晶粒内部,体积分数较大,且在其晶界处也有析出物分布,晶粒尺寸更为细小;经T6时效后的合金,第二相颗粒较大,呈分布于晶内;与经T6处理后的相比较,经T76时效后的合金具有更强的抗晶间腐蚀性能;经T76、T6时效处理后,合金的晶间腐蚀随时间变化曲线分别为:y=6.43898x^(0.43698)、y=7.72673x^(0.43702)。

700℃长时时效对LF2合金组织和高温拉伸性能的影响

研究了700℃长时时效对LF2合金组织及其高温拉伸性能的影响。结果表明:合金在700℃长时时效后存在γ′相、MC相、Laves相和σ相;γ′相呈小圆球状弥散分布于晶内,MC相和Laves相未聚集长大,σ相大量析出;MC相和Laves相对合金高温强度的影响很小;γ′相是使合金具有良好高温强度的重要析出相;σ相的大量析出是合金高温屈服强度下降的主要原因。

Al—Li—x合金的微观结构与性能

研究了Al—Mg—Li合金添加Ag元素后,其对合金性能的影响.结果证明:Ag影响合金的时效过程,不但具有明显的强化效果,而且使合金保持较高的延伸率.同时,探讨了Ag在合金沉淀强化中的作用与晶界特性机理。

温度对Al-Zn-Mg-Cu高强铝合金静态回复力学行为的影响

采用双道次热压缩实验,研究了新型Al-Zn-Mg-Cu高强铝合金铸态试样在温度300~400℃,应变速率0.01~0.1 s^(-1),变形程度33%+20%,保温0~900 s静态回复过程中的流变应力行为。结果表明:温度对该合金静态回复力学行为影响显著;(1)300℃和330℃温度较低时,变形过程中回复较慢,存储的变形能较高,保温期间的回复和再结晶使第二道次流变应力降低,表现为流变应力软化现象,且随着道次间保温时间的延长应力的软化程度增大;保温过程中析出相的出现减缓了应力软化速率;(2)温度升高到360℃和400℃时,变形过程中回复充分,存储的变形能低;变形保温后基体的固溶度高,第二道次流变应力升高,表现为流变应力硬化现象;360℃变形保温期间的回复/再结晶使得随着道次间保温时间的延长应力又逐渐降低软化,析出相减缓了应力的软化速率;而400℃变形保温期间没有回复/再结晶和析出相,所以硬化后的应力并不随着道次间保温时间的延长而发生变化。

挤压态Mg-xZn-2.8Nd-0.6Zr-0.6Cd合金组织与拉伸力学性能

采用金相显微镜、扫描电子显微镜、透射电子显微镜、万能拉伸试验机对Mg-xZn-2.8Nd-0.6Zr-0.6Cd合金的微观组织和拉伸力学性能进行研究,讨论不同Zn含量对合金力学性能的影响。研究结果表明:随着Zn含量的增加,合金的晶粒逐渐细化,双峰晶组织明显,强度总体呈上升趋势。合金B的屈服强度明显比合金C的屈服强度高,因为晶界上第二相成份的Zn/Nd原子数比发生变化,合金B(3.85%Zn,质量分数,下同)中的Zn/Nd原子数比只为1.2左右,但是其理论值为3.10,合金C(5.20%Zn)中的Zn/Nd原子数比为3.03左右,理论比值为4.11,导致了挤压过程中动态分解产物β1′相的数量在合金B中要比合金C中密集,使得合金B的屈服强度要比合金C的高。挤压后,合金D(6.54%Zn)获得了最高的屈服强度和抗拉强度,分别为340 MPa和363 MPa,而且保持了高达9%的伸长率。

Nb-V-Ti微合金化高强钢的组织演变和析出行为

利用Gleeble-3800热模拟试验机研究了低碳Nb-V-Ti微合金钢在热变形温度为810~910℃、热变形速率为0.1~10s^-1条件下的热压缩变形特性。利用金相显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、显微硬度计等手段研究了微观组织、纳米析出相和力学性能之间的关系。结果表明:热变形工艺显著影响试验钢的微观结构和力学性能,其组织主要由块状铁素体、针状铁素体、贝氏体和少量M/A岛组成。降低热变形温度,不仅能细化晶粒,还能促进针状铁素体的形成,增加M/A岛的数量。当变形速率较低时,基体中析出的碳化物存在团簇现象;变形速率增大,碳化物尺寸减小,数量也减少。当试验钢在860℃以1s^-1的速率热变形时,其组织由针状铁素体和贝氏体组成,组织分布均匀,显微硬度为255HV0.5,综合性能最优。

基于失效分析的给水泵泵轴显微组织和力学性能对比研究

以9F燃机余热锅炉给水泵断裂泵轴和供货态17-4PH不锈钢为研究对象,分析了泵轴的失效机理,并通过化学成分分析、能谱分析、光学显微镜、扫描电镜、高分辨率透射电镜和力学性能试验对两种试样在合金元素含量、微观组织和力学性能上的差别进行了分析研究。断口扫描电镜分析表明,失效泵轴断面多处呈现起伏较大的扇形台阶分布,表明给水泵泵轴属典型的扭转应力所致的多源疲劳断裂;化学成分分析表明泵轴材质错用,合金元素Cu含量偏低4%、Ni含量偏低3%,不能有效析出各种合金强化相,造成宏观力学性能降低,是泵轴失效的主要原因。拉伸试验和布氏硬度对比分析结果表明,失效泵轴较供货态17-4PH试样抗拉强度、布氏硬度较分别低500MPa和150HBW左右。相比于失效泵轴,供货态合金组织中细小均匀的柱状马氏体结构和弥散分布的第二相是17-4PH合金沉淀强化的主要来源。

含V,Nb,Ti微合金钢的微观结构及力学性能

微合金化是提高钢材力学性能的有效方法。选择在低碳锰钢中加入微量的V、Nb、Ti 3种合金元素实现微合金化。并通过工艺参数的优化,制备了V,Nb,Ti质量分数分别为0.047%,0.031%,0.025%的多组元微合金化钢,σb为805 MPa,σs为590 MPa。通过扫描电子显微镜(SEM)和透射电子显微镜(TEM)的观察,分析了合金元素的析出强化和晶粒细化对钢材力学性能的影响规律。