LY12CZ铝合金随焊锤击碾压工艺优化

针对生产现场大尺寸LY12CZ铝合金薄板(2500 mm×6000 mm×2 mm)拼焊制造过程中的热裂纹和焊接变形问题,采用自动TIG拼焊设备的动态随焊锤击碾压焊接技术对焊接工艺进行了优化.通过与常规焊接的焊接金相、力学性能试验和断口扫描电镜进行对比显示,通过工艺优化,随焊锤击碾压技术有效降低了焊接残余应力,减小了焊接变形,并使锤击碾压行为与焊接熔池的凝固过程相匹配,从而防止了LY12CZ铝合金热裂纹的产生.     

基于腐蚀等级的航空铝合金腐蚀当量关系

以LY12CZ铝合金材料试件为研究对象,以腐蚀等级为度量参数,通过试验室内开展的定级加速腐蚀试验和机场环境下该材料结构腐蚀损伤检查与腐蚀等级评估,得到了LY12CZ铝合金两种环境中腐蚀的当量折算关系系数k=0.95,进而通过该系数得到了机场环境中LY12CZ铝合金腐蚀等级随腐蚀年限的变化规律,通过与飞机LY12CZ铝合金结构机场环境中实际腐蚀损伤检查对比及文献分析,验证了所得当量关系是合理有效的。     

预热处理对铝合金LY12超塑性变形的影响

本文探讨了预备热处理对铝合金LY12超塑性变形的影响.得出CZ供应状态的铝合金LY12不需采用通常的超塑性预备热处理工艺,在最佳超塑性成形温度430℃保温4 h,以最佳应变速率ε=1.67×10-4S-1变形,可获得超塑性延伸率452%.     

6063铝合金焊件尺寸不稳定性研究

采用光干涉试验的方法系统研究了６０６３铝合金焊接件在常温状态下的尺寸不稳定变形规律，并对产生这种规律的机理进行了分析，结果表明：６０６３铝合金焊件的测量部位在焊后时效过程中发生沿纵向伸长的不稳定变形，变形发生１０天后试件尺寸趋于稳定；焊件发生尺寸不稳定变形的原因主要与焊接残余应力的松驰有关。     

NaCl溶液中包覆铝层的LY12CZ铝合金阳极极化过程EIS特征

用电化学阻抗谱(EIS)研究了LY12CZ铝合金及包覆铝层后LY12CZ铝合金在0.1mol/L NaCl溶液中的腐蚀破坏过程,根据两种条件下铝合金在不同极化电位下的EIS特征.建立与之相应的电化学等效电路模型,并分析了腐蚀机理.研究表明.阳极极化过程中两种条件下铝合金的EIS主要特征类似.Nyquist图均呈现双容抗弧.在点蚀发展过程中,包覆铝层的LY12CZ铝合金的Nyquist图高,低频容抗弧半径增大,主要是因为包铝层与LY12CZ铝合金基体之间残存的氧化膜减缓了腐蚀的发展.     

国内LY12与国外2024铝合金板材的组织与力学性能

通过采用金相(OM)、X-ray衍射(XRD)和扫描电子显微分析技术(SEM)以及拉伸力学性能测试,对比研究了国内LY12铝合金与国外2024铝合金板材的微观组织和力学性能。结果表明,国内LY12合金中的晶粒尺寸较大且不均匀,板材中存在有大量的粗大块状析出相,而国外2024铝合金晶粒均匀,粗大析出相较少,多为条状。从断口来看,国内LY12断口韧窝粗大,断口分布较多的粗大的析出相,导致其塑性较差,而且,国内LY12立方织构强度低。这些可能是造成国内LY12铝合金板材的力学性能低于国外2024板材差异的主要原因。     

动态载荷下LY12CZ的力学化学行为研究

应用动应变电极技术研究了慢拉伸状态下LY12CZ铝合金在3% NaCl溶液中的力学化学行为,考察了在慢拉伸状态下应变幅和应变速率对LY12CZ在3%NaCl水溶液中的自腐蚀电位和瞬间腐蚀电流的影响规律,并且根据腐蚀电流的变化来阐述力学化学效应的大小.结果表明,LY12CZ铝合金在慢拉伸状态下力学化学效应的大小取决于应变幅、应变速率等因素.     

Al-Mg-Sc合金与LY12CZ合金激光焊接工艺的研究

为改善LY12CZ合金焊接后的机械性能和抗腐蚀性能,采用激光表面焊接技术对Al-Mg-Sc合金和LY12CZ进行对焊.分析了金相组织、显微硬度、拉伸强度以及抗腐蚀性能,试验结果表明:采用激光焊接技术可以对Al-Mg-Sc合金和LY12CZ进行对焊,不仅可保证较高的强度,还可以获得晶粒细小、硬度高于基体的强化层,并且由于镁、钪合金元素的加入还可以提高铝合金的抗腐蚀性能.     

材料超塑变形后室温机械性能的变化和预测

超塑性材料在变形过程中往往空洞化。空洞的存在严重降低超塑成形零件的室温使用性能，因此必须建立超塑变形后材料室温机械性能变化的理论预测模型。本文以铝合金LY12CZ为例，以实验数据为基础，利用人工神经网络首次建立了预测经超塑变形后的材料室温机械性能变化的理论模型。所建模型不但可以预测铝合金LY12CZ超塑变形后的刚度．强度以及韧性等室温性能指标，而且亦能充分反映超塑变形工艺参数对其室温机械性能变化的影响规律。同时，由于本文建模方法具有通用性，因此，该模型的建立为超塑成形零件的使用性能提供了理论依据和一般方法。     

0．1mol／L NaCl溶液中不同剥蚀程度LY12CZ合金的EIS特征木

通过EXCO溶液浸泡腐蚀实验制备了不同剥蚀程度的LY12CZ合金试样．研究了不同剥蚀程度的LY12CZ合金在0．1mol／L NaCl溶液中的电化学阻抗谱(EIS)特征．结果表明：不同剥蚀程度的LY12CZ合金在0．1mol／L NaCl溶液中，EIS呈现不同特征；根据电化学阻抗谱特征可区分铝合金的剥蚀状态．研究结果为铝合金构件剥蚀的现场监检测提供了必要的依据．     

5A06铝合金焊接接头在超长寿命区间的疲劳性能

采用自行研制的TJU-HJ-I型超声疲劳试验系统对5A06铝合金TIG焊焊接接头在超长寿命区间的疲劳性能进行研究. 疲劳试验结果表明,圆柱状母材试件、圆柱状焊接接头试件和薄板状焊接接头试件,在经历107循环周次后,S-N曲线仍呈下降趋势,没有发现明显转折,传统意义上的疲劳极限并不存在. 焊接接头试件在107周次和109周次下的疲劳强度仅为母材的50%~70%. 通过扫描电子显微镜进行断口形貌观察发现:母材疲劳扩展区断口较焊接接头断口平整,瞬断区呈韧窝状,而无余高焊接接头试件存在气孔、夹杂等焊接缺陷,导致疲劳性能明显降低.     

A new method for welding aluminum alloy LY12CZ sheet with high strength

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Dimensional instability of LF21 aluminum alloy weldments at room temperature and after thermal cycles

The unstable dimensional distortion of LF21 aluminum alloy weldments at room temperature and after thermal cycles was studied by use of light interference and CMM. At the same time, distortion mechanism was analyzed from the viewpoint of mechanics and microstructure. Experimental results show that there exists obvious difference of unstable dimensional distortion between LF21 welded specimens under two conditions mentioned above. Under room temperature, dimensional variation of welded specimens will decrease gradually and finally tends to be stable during 130 h after welding. The relative elongation of welded specimen is 4.2×10-5. After thermal cycles, distortion of welded specimen is much larger than that at room temperature. After 11 thermal cycles, the dimension will tend to be stable. Dimensional unstable distortion of weldments mainly results from temperature condition, microstructure variation and relaxation of welding residual stress.     

动态压缩LY12铝合金微结构的XRD线形分析

用Hopkinson杆实验装置在不同温度下对LY12铝合金进行动态压缩实验.采用XRD线形分析对压缩试样的微细观结构演化进行研究.由XRD的积分宽度确定试样中位错为刃型位错.衍射峰形的Fourier分析表明,在动态加载下,材料内部的位错密度在塑性流动的初期迅速趋于饱和,且随着测试温发的升高,位错密度呈递减趋势,同时亚结构的尺寸不断增加.衍射峰形分析结果显示在280—300℃之间亚结构尺寸迅速增长,与LY12铝合金在280℃附近发生第:相粒子的溶解对应.     

激光焊接技术在飞机结构损伤抢修中的应用

针对目前军用飞机铝合金结构件损伤抢修技术的弊端,提出采用激光焊接技术修复损伤的结构件,通过对Al 3Mg 0.5Sc合金和2A12(LY12)合金的焊接性能的试验研究表明:Al 3Mg 0.5Sc焊缝处的性能优于2A12的性能,Al 3Mg 0.5Sc与2A12激光对焊焊缝晶粒明显细化,显微硬度与基体硬度、抗拉强度与铆接强度均相当,Al 3Mg 0.5Sc合金可应用于飞机结构件的修复。     

Superplastic deformation of duralumin LY12CZ under an electric field

The general superplastic deformation of many alloys had been studied exhaustively. Recently, the superplastic deformation of some alloys has been achieved by the application of an electric field to the process. Conrad and his colleagues have obtained the change of the flow stress and the strain-rate exponent during the superplastic deformation of 7475 Al alloy subjected to an external dc electric field. However, it is not clear how the electric field will affect the elongation and the growth of cavities quantitatively, and whether the type of cavities will change because of the existence of the external electric field.

In this paper, the optimum process parameters for the super plastic deformation of duralumin LY12CZ, without any pre-treatment, subjected to an external dc electric field have been obtained, LY12CZ (corresponding to ASTM 2024) being used widely in the aeronautic-astronautic industry. Furthermore, the effect of the electric field on the superplasticity and the superplastic-deformation conditions has been investigated. The experimental results show that the application of the electric field: (i) decreases the flow stress by 10–25% and the degree of cavitation at the onset of the fracture by 11% approximately; (ii) reduces the rate of strain-hardening; and (iii) increases the strain-rate sensitivity exponent by 26–38%. It is important to note that: (iv) the elongation of the superplastic deformation of LY12CZ under the electric field increases by 14–45% as compared with that without the electric field; (v) the equivalent strain at the onset of the rapid growth of the cavities increases by 25% with the application of the electric field; and (vi) spherical cavities exist in the specimens after the tensile test when applying the electric field, as opposed to the V-type cavities for the general superplastic deformation of LY12CZ. From these investigations, the optimum process parameters for the superplastic deformation of LY12CZ under an electric field are as follows: the deformation temperature is 471°C and the initial strain rate is 0.333 × 10⁻³ s⁻¹.     

LY12铝合金摩擦焊接过程的电场效应

定量研究了外加强电场对LY12铝合金摩擦焊接头热影响区（HFZ）中动态再结晶区宽度与晶粒尺寸的影响，并初步探讨了其影响机制。实验结果表明，外加强电场使动态再结晶区晶粒细化、等轴性提高，超细等轴晶区亦加宽。此外，采用较高焊接压力时，电场的引入使焊接接头的动态再结晶区宽度增大10％－30％；采用中等摩擦压力施焊时，电场的作用不但使焊接接头动态再结晶区宽度明显增加，而且还影响其沿径向的分布形态，使近轴心线处的动态再结晶区宽度趋于均匀，可以推断，外加强电场可使摩擦焊接头更易发生动态再结晶，而且强电场使焊合区组织的细化与均匀化，有利于提高焊接接头性能。     

DIMENSIONAL INSTABILITY OF LD31 Al ALLOY WELDMENTS AT ROOM TEMPERATURE AND AFTER THERMAL CYCLES

The unstable dimensional distortion of LD31 aluminum alloy weldments at room temperature and after thermal cycles was studied by use of light interference and CMM(three-coordinate measuring machines). At the same time, distortion mechanism was analyzed from the viewpoint of mechanics and micro structure. Experimental results show that there exists obvious difference of unstable dimensional distortion between LD31 welded specimens under two conditions mentioned above. Under room temperature, dimensional variation of welded specimens will decrease gradually and finally tends to be stable during 200h after welding. The relative elongation of welded specimen is 3.0×10-5; After thermal cycles, distortion of welded specimen is much larger than that at room temperature. After 11 thermal cycles, the dimension will tend to be stable. Dimensional unstable distortion of weldments mainly results from temperature condition, microstructure variation and relaxation of welding residual stress.     

拼焊板单向拉伸变形非均匀性

从金属塑性理论出发,结合拼焊板成形特点,推导出同材差厚拼焊板试件单向拉伸情况下缩颈时焊缝两侧薄厚板变形量公式。并基于垂直于拉伸方向居中焊缝的拼焊板单向拉伸实验,将实验结果与公式推导结果比较,初步验证了公式的合理性。进而进行了不同焊缝位置(焊缝垂直于拉伸方向,薄厚板厚度比例不同)情况下的拼焊板试件单向拉伸有限元模拟,进一步验证了所推导公式是正确的。另外,分析了单向拉伸状态下焊缝两侧薄厚板变形的非均匀特性,利用文章所提出的公式,可以定量地预测单向拉伸状态下拼焊板试件焊缝两侧材料非均匀性变形量,从而为提高焊缝两侧材料的匹配性以减小拼焊板变形的非均匀性提供了参考依据。