Effect of heat treatment on stress corrosion cracking, fracture toughness and strength of 7085 aluminum alloy

The influences of heat treatment on stress corrosion cracking （SCC）, fracture toughness and strength of 7085 aluminum alloy were investigated by slow strain rate testing, Kahn tear testing combined with scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results show that the fracture toughness of T74 overaging is increased by 22.9% at the expense of 13.6% strength, and retrogression and reaging （RRA） enhances fracture toughness 14.2% without reducing the strength compared with T6 temper. The fracture toughness of dual-retrogression and reaging （DRRA） is equivalent to that of T74 with an increased strength of 14.6%. The SCC resistance increases in the order： T6〈RRA〈DRRA≈T74. The differences of fracture toughness and SCC were explained on the basis of the role of matrix precipitates and grain boundary orecioitates.

Effect of homogenization time on quench sensitivity of 7085 aluminum alloy

The effect of homogenization time on quench sensitivity of a cast 7085 aluminum alloy was investigated by means of end-quenching test, optical microscope （OM）, scanning electron microscope （SEM） and transmission electron microscope （TEM）. The results show that with the increase of homogenization time from 48 h to 384 h, quench sensitivity increased slightly as the largest difference in the hardness was increased from 5.2% to 6.9% in the end-quenched and aged specimens. Prolonging homogenization had little effect on the grain structure, but improved the dissolution of soluble T phase and resulted in larger Al3Zr dispersoids with a low number density. Some small quench-induced η phase particles on Al3Zr dispersoids were observed inside grains during slow quenching, which decreased hardness after subsequent aging. The change in the character of Al3Zr dispersoids exerted slight influence on quench sensitivity.

Effect of hot deformation conditions on grain structure and properties of 7085 aluminum alloy

The influences of deformation conditions on grain structure and properties of 7085 aluminum alloy were investigated by optical microscopy and transmission electron microscopy in combination with tensile and fracture toughness tests. The results show that the volume fraction of dynamic recrystallization increased with the decrease of Zener-Hollomon （Z） parameter, and the volume fraction of static recrystallization increased with the increasing of Z parameter. The strength and fracture toughness of the alloy after solution and aging treatment first increased and then decreased with the increase of Z parameter. The microstructure map was established on the basis of microstructure evolution during deformation and solution heat treatment. The optimization deformation conditions were acquired under Z parameters of 1.2×10^10-9.1×10^12.

Effect of initial microstructure on hot workability of 7085 aluminum alloy

The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 ℃ and the strain rate ranging from 0.0001 to 1 s 1. The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 ℃, 0.01 s i and 450 ℃, 0.001 s-1, respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.

Microstructural evolution during homogenization of DC cast 7085 aluminum alloy

The microstructural evolution of a DC cast 7085 alloy during homogenization treatment was investigated by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry (EDS), differential scanning calorimeter (DSC) and X-ray diffraction (XRD). The results showed that serious dendritic segregation existed in the as-cast 7085 alloy. Numerous eutectic microstructures and phases were observed at the grain boundary. During homogenization process, eutecticα(Al)+T(AlZnMgCu) microstructure gradually was dissolved into matrix. IntermetallicS(Al2CuMg) phase formed and grew along the eutectic microstructure and disappeared into the matrix completely when it was homogenized at 460 °C for 24 h. It could be found that the evolution of primary eutectic structure of 7085 alloy consisted of three processes, dissolution of eutecticα+T microstructure, phase transformation fromT phase toS phase and the dissolution ofS phase. The optimum homogenization parameter was at 470 °C for 24 h.

Effect of quenching rate on microstructure and stress corrosion cracking of 7085 aluminum alloy

The influence of quenching rate on microstructure and stress corrosion cracking （SCC） of 7085 aluminum alloy was investigated by tensile test, slow strain rate test （SSRT）, combined with scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electrochemical test. The results show that with decreasing the quenching rate, the size and inter-particle distance of the grain boundary precipitates as well as precipitation free zone width increase, but the copper content of grain boundary precipitates decreases. The SCC resistance of the samples increases first and then decreases, which is attributed to the copper content, size and distribution of grain boundary precipitates.

大型7085铝合金筒形件淬火残余应力及其消减工艺研究

以大型7085铝合金筒形件为研究对象,研究了在最大程度保证铝合金大锻件性能的同时尽可能减小其淬火残余应力的方法。基于Abaqus平台,分别建立了大型筒形件淬火有限元模型和淬火后冷胀形有限元模型,考虑了淬火工艺和冷胀形工艺间的数据继承关系,分析了工艺参数对锻件性能及残余应力的影响规律。针对大型7085铝合金筒形件的淬火过程,将7085铝合金的等温转变曲线和时间-温度-性能曲线写入Abaqus用户子程序USDFLD中,计算了大型筒形件在不同淬火工艺条件下的析出相含量和分布、对应的硬度变化以及残余应力分布,获得了35℃的淬火水温是最优的选择。在消减淬火残余应力的冷胀形工艺中,基于不同的淬火水温条件开展了胀形量、胀形道次和每道次之间环转动角度的正交模拟实验,结果显示胀形量对残余应力消减的影响最显著,胀形量为4.5%时大型7085铝合金筒形件的应变均匀性最好且残余应力消减最充分。将仿真获得的优化淬火工艺和胀形方案应用于生产试制,所获得的大型筒形件各项力学性能达到设计要求,其残余应力实测结果与仿真结果对比具有较好的一致性。

Al-Ti-B微观组织对7085铝合金细化效果的影响

为比较三种Al-Ti-B的微观组织对7085铝合金晶粒尺寸、硬度及电导率的影响,利用金相显微镜、SEM、维氏硬度计和涡流导电仪等检测设备,研究了经Al-Ti-B中间合金细化后的7085铝合金显微组织与力学性能。结果表明:三种Al-Ti-B中的TiAl_(3)、TiB_(2)相形貌与平均尺寸无明显差异,微观组织缺陷较少。两种Al-5Ti-0.2B中TiB_(2)粒径尺寸分布区间较窄的细化效果较优,将Zr质量分数为0.1%的7085铝合金晶粒细化至168μm;Al-5Ti-1B中TiB_(2)粒径分布区间较窄且含量较高,可将该合金晶粒细化至112μm。窄的粒径分布区间、高的拟合度、异质形核核心数量的提升对细化效果产生积极作用,一定程度抑制了Zr“毒化”现象,改善了硬度及电导率性能。

原位纳米ZrB_(2)颗粒增强7085铝合金的微观组织与力学性能研究

本文通过原位合成技术,成功制备了纳米ZrB_(2)颗粒增强7085铝合金基复合材料。采用金相显微镜、扫描电子显微镜、透射电子显微镜、X射线衍射仪进行表征,并进行力学性能测试,研究了ZrB_(2)纳米增强体对7085铝合金的显微组织和力学性能的影响。结果表明,ZrB_(2)纳米增强体可以显著提高7085铝合金的强度。但是随着增强体体积分数增大,ZrB_(2)颗粒团聚现象加剧,不利于复合材料的塑韧性提高。同时,在复合材料中引入微量稀土元素Sc可使纳米ZrB_(2)颗粒团聚现象得到改善,并进一步细化基体晶粒,使复合材料的强度和延长率都得到提高。当ZrB_(2)含量为2%(体积分数)、Sc含量为0.4%(质量分数)时,复合材料的抗拉强度为534 MPa、伸长率为10.2%,相较于7085铝合金基体分别提高了17.4%、14.6%。

压铸态7085铝合金的热变形行为与力学性能研究

以压铸态7085铝合金为研究对象,采用三种工艺对其进行热压缩变形。采用光学显微镜(OM)对热压缩变形试样的微观组织进行观察和分析,采用电子万能试验机和扫描电子显微镜(SEM)对不同工艺下的试样进行力学性能测试和断裂行为分析。结果表明,该合金经不同道次变形后组织差别较大,单道次大应变变形后组织未发生明显的再结晶,为加工硬化状态,而多道次小应变累积的变形方式可激发少量的静态再结晶。单道次等温压缩后材料的屈服强度和抗拉强度较高,分别为402.6和480.7 MPa,断后伸长率从铸态的11.3%降低到9.3%。经固溶处理后材料的组织均匀性有明显改善,单道次等温压缩获得最佳综合力学性能,屈服强度降低到348.0 MPa,断后伸长率增加到20.9%,断口由变形态的沿晶断裂变为穿晶断裂。

7085铝合金热变形行为特征

采用光学金相、热压缩实验和本构方程计算,研究了7085铝合金在不同热变形工艺下的热变形行为。实验结果表明,在热变形温度350~460℃和变形速率0.01~10 s-1范围中,随着7085铝合金变形温度的提高和速率降低,合金的变形峰值应力随之降低,7085铝合金呈现出正应变速率敏感性;采用Arrhenius本构关系构建了7085铝合金热变形的本构模型,并建立了7085铝合金变形温度和速率范围内的热加工图,确定出7085铝合金热变形加工的合适工艺范围温度为420~460℃,应变速率0.01~0.3 s-1。在此工艺条件下,合金变形稳定且易于金属流动。

Effects of Cu/Mg ratio on microstructure and properties of AA7085 alloys

AA7085 aluminum alloys with different Cu/Mg ratios （0.67, 1.0, 1.06, 1.6） were prepared by ingot metallurgy method. The effects of Cu/Mg ratio on the microstructure, mechanical properties and corrosion behavior of the AA7085 alloys were investigated by optical microscope, scanning electron microscope （SEM）, mechanical properties and corrosion testing. The results indicate that a better recrystallization inhibition and corrosion resistance can be achieved when Cu/Mg ratio is 1.6. When Cu/Mg ratio is 0.67, the alloy reveals better mechanical properties, and the tensile strength and yield strength of AA7085 alloys are 586 and 550 MPa, respectively. Moreover, both the mechanical properties and corrosion resistance of the alloy are reduced when Cu/Mg ratio is equal to 1.0.

含Sr7085型铝合金的晶间腐蚀和剥落腐蚀性能

对一种Sr微合金化的7085型铝合金的晶间腐蚀性能和剥落腐蚀性能进行了研究。结果表明,该合金经均匀化退火、热压缩变形加工、强化固溶(470℃×2 h+480℃×2 h+490℃×2 h)处理、冷水淬火、T6(120℃×24 h)时效处理后,具有很好的抗晶间腐蚀性能和抗剥落腐蚀性能,其抗腐蚀性能明显优于7075-T6合金。按GB 7998-2005(ASTM G110-1992)晶间腐蚀试验标准,该合金未发生晶间腐蚀,仅发生点蚀。按GB/T 22639-2008(ASTM G34-2001)剥落腐蚀试验标准,其剥落腐蚀等级为PA级。该合金所具有的优异抗腐蚀性能与其具有较低的合金元素总量(10.073%)、较高的w(Zn)/w(Mg)(4.97)比和w(Cu)/w(Mg)(1.06)比以及Zr和Sr的微合金化作用(细化组织、抑制再结晶)是一致的。

时效处理对7085铝合金锻件组织和腐蚀性能的影响

采用慢应变速率拉伸试验、剥落腐蚀试验、极化曲线及透射电镜等分析方法,研究时效处理对7085铝合金锻件腐蚀性能的影响。研究结果表明:与T6时效合金相比,合金经T74时效的抗应力腐蚀和抗剥落腐蚀性能提高但强度显著降低;经RRA时效处理,合金保持了较高强度的同时,应力腐蚀性能敏感性降低,抗剥落腐蚀性能提高;在腐蚀溶液中,极化曲线测试也表现出同样的趋势;合金经过RRA时效处理,形成粗大且不连续的晶界析出相是提高腐蚀性能的主要原因。

7085铝合金的热变形组织演变及动态再结晶模型

通过等温压缩实验,系统研究热变形参数(变形温度、应变速率及应变量)对7085铝合金热变形组织演变的影响。结果表明:升高变形温度以及降低应变速率,均有利于7085铝合金的动态再结晶发生,导致变形后的7085铝合金位错密度降低,再结晶晶粒尺寸增大;随着应变量的增加,变形后的合金位错密度降低,动态再结晶体积分数增大。采用线性回归方法建立包括峰值应变方程、临界应变方程、动态再结晶动力学方程以及动态再结晶晶粒尺寸方程的7085铝合金动态再结晶模型。

双级时效对7085铝合金组织和性能的影响

采用硬度、电导率、力学拉伸、慢应变速率拉伸试验及透射电镜等测试分析方法,研究双级时效对7085铝合金组织和性能的影响。结果表明:预时效热处理主要析出相为GP区和η′相,预时效时间对合金硬度和电导率的影响较小。随着第二级时效时间的延长,合金的抗拉强度和屈服强度先增大后减小,电导率和抗应力腐蚀性能提高,晶界析出相由连续分布变为非连续分布。第二级时效温度越高,合金强度随时效时间的延长,降低得越显著。采用(110℃,6 h)+(160℃,12 h)双级时效热处理,合金的抗拉强度、屈服强度、伸长率及电导率分别为515MPa、487MPa、11.7%、38%(IACS)。

淬火速率对7085铝合金时效行为的影响

通过末端淬火实验、硬度测试、透射电子显微镜和差示扫描量热法,研究淬火速率对7085铝合金时效行为的影响。结果表明:在末端淬火过程中,距离淬火端越近,淬火速率越大,时效后的峰值硬度越高。当时效温度较低时,淬火速率越大,则空位扩散激活能越小,时效处理后的硬度达到峰值的时间越短,硬度值越大;随着时效温度的提高,不同淬火速率样品达到峰值的时间不断接近;当时效温度达到160℃时,不同淬火速率样品达到峰值的时间相同,均为10 h。TEM分析结果表明:随着淬火速率降低,淬火过程中析出的平衡相η数量和尺寸也随之增加,时效后析出的强化相η'数量减少,尺寸增加,弥散程度降低。

7085铝合金热压缩变形的流变应力本构方程

采用Glecbc-1500热模拟机对7085铝合金进行热压缩，研究了该合金在应变速率为1～38s^-1、变形温度为260-440℃条件下的流变应力行为。结果表明，7085铝合金流变应力在变形初期随着应变的增加而增大，出现峰值后逐渐趋于平稳；峰值应力随应变速率的增加而增加，随温度的升高而降低；通过线性回归分析计算出7085材料的应变硬化指数n以及变形激活能Q，获得了7085铝合金高温条件下的流变应力本构方程。

强化固溶处理对7085铝合金组织与性能的影响

采用光学显微镜(OM)、电子背散射衍射检验(EBSD)、X射线衍射仪显微分析(XRD)、拉伸性能测试,研究了强化固溶处理对7085铝合金组织与性能的影响,并分析了其强化机理。结果表明:与常规固溶相比,强化固溶处理使合金的强度显著提高,伸长率变化不大;经时效处理后的7085铝合金的屈服强度为471.8 MPa、抗拉强度为518.3 MPa、伸长率为14.7%;通过对强化机理的分析,强度的提高主要来自于析出沉淀相强化。

预回复退火对7085铝合金挤压材组织和性能的影响

通过光学显微镜(OM)观察、拉伸试验、XRD及EBSD检测分析,研究了预回复退火对7085铝合金微观组织性能的影响,并对其强化机理进行了初步研究。结果表明,预回复退火处理可有效细化7085型铝合金挤压材晶粒尺寸,抑制再结晶,提高拉伸力学性能;强度提高归因于低角度晶界及位错强化。