铝合金厚板淬火-预拉伸残余应力的有限元仿真

利用MSC.Marc非线性有限元软件建立了一个淬火-预拉伸模型,并利用该模型对7075铝合金厚板进行了仿真研究。仿真结果表明,对于7075铝合金的最佳拉伸量为2.0%～2.5%,预拉伸后板内残余应力降低幅度可达90%以上,且残余应力分布形式由淬火态的"M"型演变为预拉伸后的"W"型;随着拉伸量的增加铝板内塑性变形合格的区域逐渐增加,可利用预拉伸中的等效应力分布状态确定锯切区。若提供适当的残余应力测试结果,利用有限元仿真模型可有效地揭示铝合金厚板淬火-预拉伸内部残余应力的演变规律。     

7075铝合金预拉伸板淬火后残余应力的有限元模拟

运用有限元软件MSC.MARC对7075铝合金板材淬火过程进行模拟.在获得淬火残余应力的基础上,假设钳口夹持区域为理想刚端,根据材料力学、金属塑性变形等基本原理,利用有限元数值模拟计算方法,建立起该状态下的预拉伸模型.模拟了不同预拉伸量和不同拉伸速度对削减毛坯淬火残余应力的影响以及计算了钳口夹持区域的锯切量.结果表明:拉伸量为3%时,残余应力消除量约为96%,锯切量为21.6%,完全符合航空铝合金厚板生产工艺的规定.     

7075铝合金预拉伸板消除残余应力的试验研究

铝合金预拉伸厚板是现代航空工业的重要结构材料，但厚板淬火残余应力的存在不仅使其在机加工过程中易出现翘曲变形，而且也明显降低材料的动态使用性能加KIC、KQC、抗腐蚀和疲劳性能。对7075铝合金厚板淬火时残余应力的分布进行了试验研究，结果表明：通过控制淬火介质的温度，能有效降低淬火后厚板中的残余应力。此外，通过分析淬火过程中残余应力的产生机理，提出了两种降低淬火过程中残余应力的新方法。     

淬火温度对7075铝合金厚板残余应力的影响

对7075铝合金厚板进行固溶处理后,分别在不同的淬火水温下进行浸没淬火和喷淋淬火。运用X射线衍射法测试淬火板的表面残余应力,利用维氏硬度仪测试板表面显微硬度,研究淬火工艺及水温对铝合金厚板残余应力与力学性能的影响。结果表明:随淬火温度的升高,浸没淬火与喷淋淬火引入的表面残余压应力水平与表面显微硬度迅速下降,且在一定的温度下,前者比后者引入的残余应力水平大40%,而显微硬度仅大7%。     

预拉伸对7075铝合金厚板残余应力分布的影响

运用有限元法对7075铝合金厚板预拉伸过程进行了数值模拟,获得了预拉伸板内部的残余应力分布,研究了预拉伸量对残余应力演变的影响.采用裂纹柔度法对淬火板和预拉伸板(拉伸量分别为1.8%、2.2%和2.5%)进行了残余应力检测,计算得到了不同工艺下铝厚板内部的残余应力分布.结果表明:预拉伸能够大幅消减淬火残余应力,当拉伸量为2.2%左右时,残余应力减少至±20MPa,能够满足后续加工的要求.     

7075铝合金厚板预拉伸模拟分析及其在淬火残余应力消除中的应用

运用有限元软件ABAQUS, 对7075铝合金板材淬火过程进行了模拟.比例件的加工变形表明淬火模拟所得的残余应力是可信的.在获得淬火残余应力的基础上, 模拟了不同预拉伸量对毛坯的淬火残余应力的消除.结果表明: 拉伸量为3%时, 毛坯产生2.1%～2.6%的永久变形, 残余应力消除量约为86%, 完全符合航空铝合金厚板生产工艺的规定.     

超声波残余应力测试技术在工程实际中的应用

对超声波法残余应力测试技术在铝合金厚板工程实际中的应用进行了研究,分析了不同7050铝合金厚板在不同工序和不同板厚下的应力状态。结果表明,7050厚板表面残余应力沿板材宽度方向呈小幅的随机波动,波动的数值在设备的测试误差之内,残余应力在板材宽度方向是均匀分布。7050厚板的表面残余应力在不同工序处理后残余应力存在较大差异,热轧后应力很小,淬火后应力很大且为压应力,预拉伸和时效后应力整体水平很小,热轧工序对厚板残余应力的影响较小,厚板内部较高的残余应力主要来自于淬火工序。通过预拉伸工序可有效消减淬火产生的残余应力,可使厚板整体应力水平满足使用要求。不同厚度的7050厚板表面残余应力均处于较低的水平,随着厚板厚度的增加,表面残余应力略有增大。     

预拉伸变形量对7055铝合金厚板表面残余应力的影响

为了系统性地研究预拉伸变形量对淬火残余应力的消减规律,采用基于cosα法的μ-X360s型X射线残余应力分析仪,表征7055铝合金厚板经不同预拉伸变形量(0%、0.5%、1.2%、1.5%、2.5%、3.3%、3.9%)的表面残余应力水平,并通过基于sin2Ψ法的X射线衍射法和钻孔法验证测试结果。结果表明:7055铝合金厚板经过固溶淬火处理后,残余应力水平较高,轧向分应力略小于横向分应力,在厚板边缘区域残余应力水平波动较大,波动区域大约在距边部27mm的位置。当预拉伸变形量为1.5%时,轧向分应力的明显减小,继续增大拉伸量,残余应力稳定在60~70 MPa;而当预拉伸变形量大约为1.5%时,横向分应力由压应力状态转变为拉应力状态;经超过2.5%的预拉伸变形后,残余应力稳定在20~30 MPa。     

航空铝合金厚板残余应力数值模拟研究现状

为获得理想性能,航空铝合金厚板在生产过程中需经历轧制、固溶淬火、预拉伸和时效强化等工艺过程。其中,厚板在进行固溶淬火处理时整体温度变化异常剧烈,内部产生较高残余应力。近年来,借助数值模拟的手段分析铝合金厚板内部固溶淬火残余应力分布状态并对其进行消减处理是研究关注的热点。介绍基于有限元方法的7xxx系航空铝合金厚板固溶淬火及预拉伸处理过程中板材内部残余应力演化规律研究现状,对固溶淬火和预拉伸仿真计算过程中所用方法及模型参数进行归纳,展望该领域未来的重点研究内容和发展方向。     

7050铝合金超厚板喷淋淬火的数值模拟分析

基于有限元模拟软件ABAQUS,建立有限元模型对铝合金超厚板的喷淋淬火过程进行参数化模拟,来探究铝合金超厚板在不同淬火条件下的残余应力分布规律。研究表明:淬火过程中,铝合金超厚板厚度方向的残余应力分布逐渐由"外拉内压"转变为"外压内拉"的状态;改变喷淋压力和淬火水温可以改变厚板淬火残余应力分布规律,厚板中心的残余应力随着淬火水温的升高而降低。随着喷淋压力的提高,厚板中心的残余应力呈现出先降低后上升最后趋于稳定的变化趋势,并在喷淋压力为200 kPa时出现应力的最小值。     

Residual stress in quenched 7075 aluminum alloy thick plates

1　INTRODUCTION70 75isoneoftheprecipitation hardenedalu minumalloysmainlyusedasplateandforgingsintheaerospaceindustry .Itshighstrengthisachievedthroughaquenchingoperationwherethematerialisrapidlycooledfromthesolutionheattreatmenttem perature(4 75℃ )toroomtemperature ,whichcancausetheadverseeffectofintroducingresidualstress ,leavingthematerialunsuitableforfurthermachiningoperationsandforservice[13] .Residualstressinthequenchingoperationforaluminumalloysisusuallystudiedbynumericalprediction…     

Dry and clean age hardening of aluminum alloys by high-pressure gas quenching

When precipitation-hardenable aluminum parts are water quenched, distortion occurs due to thermal stresses. Thereby, a costly reworking is necessary, and for this reason polymer quenchants are often used to reduce distortion, with the disadvantage that the quenched parts have to be cleaned after quenching. In opposition to liquid quenchants, gas quenching may decrease distortion due to the better temperature uniformity during quenching. Furthermore, cleaning of the quenched parts can be avoided because it is a dry process. For this purpose, a heat-treating process was evaluated that included a high-pressure gasquenching step. Gas quenching was applied to different aluminum alloys (i.e., 2024, 6013, 7075, and A357.0), and tensile tests have been carried out to determine the mechanical properties after solution annealing, gas quenching, and aging. Besides high-pressure gas quenching, alloy 2024 was quenched at ambient pressure in a gas nozzle field. The high velocity at the gas outlet leads to an accelerated cooling of the aluminum alloy in this case. Aluminum castings and forgings can be classified as an interesting field of application of these quenching methods due to their near-net shape before the heat treatment. Cost savings would be possible due to the reduced distortion, and therefore, less reworking after the precipitation hardening.     

2A70铝合金预拉伸厚板热处理工艺研究

介绍了固溶处理温度、淬火到时效间隔时间及时效制度等对 2A70铝合金预拉伸厚板组织和性能的影响 ;对其影响机理进行了分析和探讨 ;确定了 2A70铝合金预拉伸厚板的热处理工艺参数。     

热处理制度对7075铝合金电导率的影响

试验研究了7075铝合金板材不同热处理制度与电导率的关系,指出生产中可利用电导率来初步判定7075铝合金板材的热处理质量。     

预拉伸对新淬火态2A12硬铝合金残余应力和力学性能的影响

对新淬火态2A12硬铝合金不同预拉伸量下的残余应力和力学性能进行了研究,得到了取得最小残余应力值的预拉伸量,分析了新淬火态铝合金薄板表面残余应力的方向问题,并对屈服强度和抗拉强度在不同拉伸量下的分布规律作了探讨。     

Effect of pitting corrosion on fatigue performance of shot-peened aluminium alloy 7075-T651

Pitting corrosion has a major influence on aging of structural elements made of high-strength aluminium alloys as corrosion pits lead to earlier fatigue crack initiation under tensile dynamic loading. A cause of fatigue crack initiation in a corrosive medium is a stress concentration at a corroded area. In order to improve material resistance to corrosion fatigue it is necessary to reduce pit-tip stresses. To eliminate or reduce pit stresses, cold surface hardening by shot peening was proposed. The objective of the present study was to investigate the effect of surface hardening by shot peening on electrochemical stability and corrosion fatigue properties of high-strength aluminium alloy 7075-T651 in the corrosive environment of a chloride solution. The results obtained show a favourable influence of shot-peening treatment on corrosion fatigue properties. Induced compressive residual stresses in the surface layer retard the initiation of fatigue cracks, and so the fatigue life improvement of structural elements made of high-strength aluminium alloys was observed.     

2195合金锻造管的淬火与时效工艺

研究了2195合金大规格锻造管的淬火与时效工艺。通过拉伸试验、金相显微仪和透射电镜考察了热处理工艺参数对其力学性能和显微组织的影响。淬火敏感性试验表明,产品必须采用水冷方式淬火,但对冷却水的温度可以不作严格控制。不同温度的人工时效工艺试验表明,低温峰值时效可以使产品获得较高的强度和理想的伸长率,而时效温度升高将导致沉淀相粗化,使产品的强度下降。合理的2195合金锻造管的淬火工艺为500℃固溶、水冷淬火,人工时效制度为150℃时效195 h。     

On the applicability of high strength self‐tapping aluminium bolts in magnesium nut materials for automotive applications

High strength aluminium bolts made of AW 6056 T6, AW 7075 T6 and T79 have been investigated regarding the applicability in magnesium nut materials for automotive applications. With respect to galvanic corrosion all combinations of aluminium bolts with magnesium parts show superior corrosion properties when compared to galvanised steel bolts connected to magnesium. With respect to stress corrosion cracking (SCC) no aluminium bolt in contact with magnesium failed due to SCC. This is because of cathodic protection of aluminium alloy through magnesium. Even peak‐tempered highest strengthened T6 7xxx aluminium bolts can be used for automotive applications when compressive residual stresses are present in the thread root of the bolts.