Impact Damage Identification of Aluminum Alloy Reinforced Plate Based on GWO-ELM Algorithm

As a critical structure of aerospace equipment,aluminum alloy stiffened plate will influence the stability of spacecraft in orbit and the normal operation of the system.In this study,a GWO-ELM algorithm-based impact damage identification method is proposed for aluminum alloy stiffened panels to monitor and evaluate the damage condition of such stiffened panels of spacecraft.Firstly,together with numerical simulation,the experimental simulation to obtain the damage acoustic emission signals of aluminum alloy reinforced panels is performed,to establish the damage data.Subsequently,the amplitude-frequency characteristics of impact damage signals are extracted and put into an extreme learning machine(ELM)model to identify the impact location and damage degree,and the Gray Wolf Optimization(GWO)algorithm is employed to update the weight parameters of the model.Finally,experiments are conducted on the irregular aluminum alloy stiffened plate with the size of 2200 mm×500 mm×10 mm,the identification accuracy of impact position and damage degree is 98.90% and 99.55% in 68 test areas,respectively.Comparative experiments with ELM and backpropagation neural networks(BPNN)demonstrate that the impact damage identification of aluminum alloy stiffened plate based on GWO-ELM algorithm can serve as an effective way to monitor spacecraft structural damage.

Ageing behavior of an Al-Zn-Mg-Cu alloy pre-stretched thick plate

The ageing behavior of a pre-stretched thick plate of Al-Zn-Mg-Cu alloy was systemically studied including one-step ageing, two-step ageing, and retrogression and reageing treatment （RRA）. One-step ageing of the alloy resulted in peak ultimate tensile strengths of 595 and 575 MPa after 22 and 6 h at 120 and 135°C, respectively. The strengthening phase in peak aged （T6 temper） alloy contained GP zones and the η′ phase predominantly. After two-step ageing, the electrical conductivity was increased markedly, but the pre-stretched thick plate sacrificed a great loss of strength. RRA treatment provided a method for maintaining the strength close to that obtained by T6 temper and for obtaining the high electrical conductivity close to that obtained by T7 temper; the ultimate tensile strength and electrical conductivity were 583 MPa and 21.0 MS/m, respectively. TEM analysis of T7 and RRA specimens revealed two types of precipitates that contributed to age strengthening i.e. the η′ and η phases.

Transverse stress-strain evolution during welding of thin aluminum alloy plate

The FE simulation results of transverse stresses and strains during welding of thin aluminum alloy plate are presented. The results indicate that restraint condition is the main factor that determines whether or not hot cracking will occur. With rigid restraint hot cracking (crater cracking) will occur at the arc-stopping end, and such cracking usually will not occur without external restraint. But under restraint-free condition it is easy for terminal cracks to occur.

Rotating extrusion technique and its effect on quality of aluminum alloy thin-plate weldments

A new technique named rotating extrusion was proposed that uses rotating extrusion action to rectify residual distortion of aluminum alloy thin-plate weldments to improve mechanical properties of welded joints. The basic principle and device of rotating extrusion were introduced. The residual distortion and stresses in rotating extrusion weldments were compared with those in conventional weldments. The differences in microstructure and mechanical properties between conventional welded joints and rotating extrusion welded joints were investigated and analyzed in order to make clear the effect of rotating extrusion on the performance of aluminum alloy weldments. Experimental results show that rotating extrusion can enhance the hardness and tensile strength of aluminum alloy welded joints evidently. This method has also potential effect on extending the life of welded structures.

Modified Layer-Removal Method for Measurement of Residual Stress in Pre-stretched Aluminium Alloy Plate

Residual stress is one of the factors affecting the machining deformation of monolithic structure parts in the aviation industry. Thus,the studies on machining deformation rules induced by residual stresses largely depend on correctly and efficiently measuring the residual stresses of workpieces. A modified layer-removal method is proposed to measure residual stress by analysing the characteristics of a traditional layer-removal method. The coefficients of strain release are then deduced according to the simulation results using the finite element method( FEM). Moreover,the residual stress in a 7075T651 aluminium alloy plate is measured using the proposed method,and the results are then analyzed and compared with the data obtained by the traditional methods. The analysis indicates that the modified layer-removal method is effective and practical for measuring the residual stress distribution in pre-stretched aluminium alloy plates.

Residual stress in quenched 7075 aluminum alloy thick plates

The influence of quenching water temperature, pre stretching amount and aging temperature and times on residual stress in 7075 aluminum thick plate was studied by the measurement of residual stress using drilling hole method. The results indicate that residual stress decreases by 30% with increasing quenching water temperature from 40 ℃ to 80 ℃, 20% with increasing aging temperature from 100 ℃ to 180 ℃,and 20% with increasing aging times from 5 h to 25 h. Also, residual stress decreases to zero with increasing pre stretching amount to approximately 2%. Hence, residual stress in 7075 aluminum thick plate is reduced by the control of quenching water temperature at 80 ℃ and with pre stretching amount of about 2%. An optimal aging temperature and time should be systemically investigated to obtain combination of high mechanical performances and lower residual stress for manufacturing of 7075 aluminum alloy thick plates.

Prediction model of residual stress field in aluminum alloy plate

Residual stress distributions in 7075 aluminum alloy thick plates with different thicknesses and different quenching speeds were measured. A shape function of stress distribution was proposed based on the internal stress distribution characteristics of aluminum alloy. Using nonlinear regression technology,the function between stress value of key points on internal stress curve and surface stress of the plate was obtained. Based on the measured surface stress,stress value of key points and stress distribution shape,the internal stress distribution can be reconstructed. The experiments show that the model is of good engineering practicality.

Low temperature bonding of LD31 aluminum alloys by electric brush plating Ni and Cu coatings

Soldering of LD31 aluminum alloys using Sn-Pb solder paste after electric brush plating Ni and Cu coatings was investigated. The technology of electric brush plating Ni and Cu was studied and plating solution was developed. The microstructure of the coatings, soldered joint and fracture face were analyzed using optic microscopy, SEM and EDX. The shear strength of soldered joint could reach as high as 26.83MPa. The results showed that reliable soldered joint could be obtained at 230℃, the adhesion of coatings and LD31 aluminum alloy substrate was high enough to bear the thermal process in the soldering.

Effect of deposition parameters on mechanical properties of TiN films coated on 2A12 aluminum alloys by arc ion plating (AIP)

TiN films were deposited on 2A12 aluminum alloy by arc ion plating (AIP). The Vickers hardness of the films deposited at different bias voltages and different nitrogen gas pressures, and that of the substrate were measured. The surface roughness of the TiN films diposited at –30 V and –80 V respectively and at different nitrogen gas pressure was measured also. The mass loss of TiN films deposited at 0 V, –30 V and –80 V respectively were analyzed in dry sand rubber wheel abrasive wear tests and wet ones in comparison with uncoated Al alloy and austenitic stainless steel (AISI 316L). It is revealed that the highest hardness of the TiN film is obtained at a bias voltage of –30 V and a N2 gas pressure of 0.5 Pa. The surface roughness of the film is larger at –80 V than that at –30 V and reduces as the increase of the N2 gas pressure. The mass loss of TiN-film coated 2A12 aluminum alloy is remarkably less than that of uncoated Al alloy and also that of AISI 316L, which indicates that the abrasive wear rate is greatly reduced by the application of TiN coating. TiN coating deposited by arc ion plating (AIP) technique on aluminum alloy can be a potential coating for machine parts requiring preciseness and lightness.

High-Velocity Projectile Impact Behaviour of Friction Stir Welded AA7075 Thick Plates

In this study, high velocity impact behaviour of friction stir welded AA7075-T651 25 mm thick plates were investigated using a 7.62 mm × 51 mm lead core and 7.62 mm × 39 mm steel core projectiles. Prior to ballistic trails, mechanical and metallurgical properties of friction stir welded AA 7075-T651 25 mm thick plates were studied. Microstructural and hardness studies revealed that friction stir welds constituted three distinct regions namely Weld Nugget(WN), Thermo-Mechanically Affected Zone(TMAZ) and Heat Affected Zone(HAZ). Base Material(BM) and all three weld regions were ballistically tested as per military standard NIJ.0108.01 using lead and steel core bullets at maximum permissible velocities of 830 ± 20 and 700 ± 30 m/s, respectively. It has been found that base material(AA7075-T651)and all three weld regions of 25 mm thick plates were able to resist perforation by both types of projectiles used. However depth of penetration has been found to increase from BM to WN, HAZ and TMAZ for both types of projectiles. In all cases steel core projectiles caused higher depth of penetration compared to those caused by lead core projectiles. TMAZs of the friction stir welds were found to be the weakest zone. The fracture that occurred in the base material was spall fragmentation indicating brittle failure, whereas all zones of friction stir welded AA7075-T651 targets with a front petalling, indicating ductile failure. The post-ballistic tested samples showed no significant change in the microstructure of the BM and WN. On the other hand, TMAZ and HAZ showed severe grain deformation in the direction of projectile penetration, and the formation of adiabatic shear bands(ASB). This work showed that 25 mm thick friction stir welded AA7075-T651 joints responded well to ballistic impact loads, making them a good choice for light combat vehicles.

大厚度铝合金板疲劳裂纹扩展特性研究现状及关键问题探讨

试样厚度增加引发的裂纹扩展“马鞍效应”是厚度与三维裂纹端部应力应变场内在联系的表象反映,在未得出这种内在联系机理与规律的情况下,基于传统模型对大型机械设备中的厚板及变厚度板进行损伤容限评定必然存在很大的风险。以大厚度铝合金板为研究对象,从三维裂纹端部应力应变场与裂纹扩展形貌之间的关系、疲劳裂纹扩展的厚度效应、腐蚀与疲劳共同作用下裂纹扩展机理与模型等三个方面,对裂纹扩展相关问题的研究现状进行了总结分析,对大厚度铝合金板疲劳裂纹扩展特性研究的关键问题进行了探讨。

基于电接触强化的铝合金表面电刷镀镍层改性研究

[目的]对铝合金进行表面处理可提高其硬度和耐磨性,拓宽铝合金材料在机械零件方面的应用。[方法]采用电刷镀技术在1060铝合金表面制备Ni镀层,再通过电接触强化技术对Ni镀层进行改性。采用扫描电子显微镜和维氏硬度计考察了Ni镀层电接触强化前后的微观组织和显微硬度。通过摩擦磨损试验对比了1016铝合金及Ni镀层电接触强化前后的耐磨性。[结果]经电接触强化后,Ni镀层内部的裂纹及孔洞类缺陷减少,晶粒间隙减小,致密性提高,显微硬度增大到524.4~560.3 HV0.1范围内。1016铝合金在摩擦磨损试验后存在较深的犁沟和剥落,耐磨性较差。Ni镀层的耐磨性优于1016铝合金,但在摩擦过程中会发生剥落。经电接触强化的Ni镀层在摩擦过程中摩擦因数平稳,表面只是轻微擦伤,耐磨性最佳。[结论]结合电刷镀镍和电接触强化技术可显著提高铝合金的表面性能。

前箱熔体温度对8011铝合金铸轧板坯组织性能的影响

为了稳定提高双零铝箔用铸轧坯料质量,使用电解铝液配料生产规格为7.0 mm×1300 mm的8011铝合金铸轧铝板卷,并利用光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)及电子万能拉伸试验机等手段,研究了不同前箱铝熔体温度(680,690,700,710℃)对8011铝合铸轧板坯微观组织和力学性能的影响.结果表明:随着前箱熔体温度的升高,铸轧板坯晶粒的尺寸呈略微增大再急剧变大的趋势,其抗拉强度和断后伸长率均呈先缓慢降低后急剧下降的趋势;当前箱熔体温度控制在680~700℃时,可获得综合力学性能较佳的铸轧板坯,其平均纵向抗拉强度和横向抗拉强度分别不低于141.87 MPa和138.84 MPa,平均纵向断后伸长率和横向断后伸长率分别不低于29.8%和26.4%.

表面改性对铁基非晶合金微波吸收性能的影响

目的旨在调节铁基非晶合金(IAA)粉体复合材料的微波吸收性能。方法先在铁基非晶合金粉体表面采用磁控溅射局部覆盖铝膜,再使用KH560硅烷偶联剂对粉体进行绝缘包覆。通过XRD、SEM和FT-IR分别对粉体进行材料表征,采用VSM和传输反射法分别测试样品的电磁性能。结果镀铝后铁基非晶合金粉体的复介电常数实部εʹ提高了56.1%,复介电常数虚部εʺ提高了132.4%。绝缘包覆后铁基非晶合金粉体的εʹ降低变为铁基非晶合金的32.6%,εʺ变为铁基非晶合金的25.1%。镀铝再包覆KH560的铁基非晶合金粉体的εʹ和εʺ则分别变为铁基非晶合金的43.5%和36.6%,其复介电常数实部和虚部比镀铝后的样品低,比单纯用KH560包覆后的样品高,显示出镀铝可补偿因KH560绝缘包覆而带来的介电损耗能力下降,有利于调节KH560绝缘包覆的粉体材料的电磁性能。结论对铁基非晶合金粉体的绝缘包覆,改善了相应材料的高频吸收性能,但牺牲了其低频吸收性能,为了弥补这个不足,提出在铁基非晶合金粉体表面局部覆盖铝膜,再进行绝缘包覆,期望在绝缘包覆后,粉体仍有较高的介电损耗能力,达到调节材料中低频电磁波吸收能力的目的。样品模拟反射率曲线显示,样品厚度在2~3 mm时,铁基非晶合金/Al/KH560样品最低峰对应频率低于铁基非晶合金/KH560的相应峰位,铁基非晶合金粉体表面镀铝可明显改善其复合材料的低频微波吸收特性。

基于DBSCAN算法与GMM理论的铝合金板孔边疲劳裂纹萌生监测

针对航空结构中多孔铝合金板在疲劳载荷作用下的孔边裂纹萌生监测问题,以光纤传感系统为基础结合小波分解、含噪声的密度空间聚类以及高斯混合模型,提出了一种孔边裂纹萌生监测方法。首先以光纤光栅传感系统采集循环加载条件下多孔铝合金板孔边裂纹萌生至结构断裂全程中孔边微应变并构建孔边微应变曲线。对孔边微应变曲线进行小波分解,得到微应变曲线的低频分量与高频分量,并以低频分量最小值及高频分量突变作为孔边裂纹萌生特征。在分析裂纹萌生时引入DBSCAN算法与GMM理论用于计算孔边裂纹萌生时的疲劳加载循环数并进行比较与分析得到多孔铝合金板孔边主裂纹的萌生位置以及孔边主裂纹裂纹萌生时的疲劳加载循环数。试验结果表明:此监测方法能够准确定位出孔边主裂纹的萌生位置,计算孔边主裂纹萌生时的疲劳加载循环数,且疲劳加载循环数计算误差在5%以内。在未来可应用于全机地面疲劳试验、结构健康监测等多种场景。

铝合金电镀金鼓包原因分析及解决措施

铝合金零件镀金层出现鼓包故障,扫描电镜结果显示鼓包位置有晶间腐蚀形貌,沿晶腐蚀与表面贯通。镍层在局部位置沿晶裂纹渗入到基体内,且在沿晶裂纹内存在P元素。说明沿晶腐蚀在镀镍前已经存在,电镀后晶间腐蚀处被镀层覆盖,因此在结合力检测过程中,在晶间腐蚀产生应力的作用下,该处形成鼓包现象。机械加工和电镀过程中采取一系列防锈措施后,解决了该故障。

适用于航空航天铝合金件的镀多层镍工艺

[目的]航空航天铝合金件镀镉工艺亟需找到环保的替代技术。[方法]制定了一种镀多层镍工艺,其工艺流程主要包括化学除油、超声波除油、碱腐蚀、出光、除垢、微腐蚀、第一次沉锌、退锌、第二次沉锌、化学预镀镍、镀半光亮镍、镀高硫镍、镀光亮镍、稀土电解保护和烘干。[结果]这种镀层在进行168h中性盐雾试验后无锈蚀,220℃热震试验中无起泡和脱落,在温度40℃和相对湿度93%的条件下进行的1000h恒定湿热试验后无可见变化。[结论]该工艺克服了单一化学镀镍层对铝合金基体无电化学保护作用的缺点,并以新开发的稀土电解保护工艺代替了传统的铬酸盐电解保护法,绿色环保,具有良好的应用前景。

新能源汽车铝电池盒MIG焊接新工艺

在铝合金电池盒实际生产中,由于焊接位置较多、焊接接头板厚差异大,焊接一次合格率很难控制,这就需要研发一种焊接工艺提升铝合金薄厚板焊接的稳定性。目前铝合金电池盒MIG焊接主要是直流脉冲焊接,其中包括直流单脉冲或直流双脉冲焊接。通过分析发现,采用直流+交流摆动同步双脉冲焊接,在相同电流情况下可有效降低焊接热输入,在相同热输入情况下可增加焊缝a值。并在铝合金薄厚板焊接时,可在厚板位置使用直流脉冲,薄板位置使用交流脉冲,保证厚板熔深且薄板不烧穿。摆动同步交直流焊接技术已经在实际生产中得到应用,并有效提高了焊缝合格率和生产效率。

3D打印铝合金液冷板在冷却液中的静态腐蚀

目的 对比3D打印铝合金液冷板材料经不同表面处理后在冷却液中的静态腐蚀情况,并预测静态腐蚀速率。方法 通过p H值测试、腐蚀表面形貌分析来监测冷却液和铝合金的变化,通过电化学方法测试样件的腐蚀动力学参数,通过质量损失试验测量材料的腐蚀速率和年腐蚀深度,通过EDS分析腐蚀产物。结果 所有试验组冷却液p H均整体呈下降趋势。在试样表面可以观测到明显的腐蚀现象,集中发生于试样表面的缺陷位置。不同表面处理的样件,其腐蚀速率不同,差异最大可达16倍。冷却液中的有效缓蚀成分参与了试样表面腐蚀产物膜的形成,在表面沉积了P、Ca等元素。结论 3D打印成形铝合金材料在冷却液中的年腐蚀深度整体较小,其耐蚀性良好,进行液态磨粒抛光或酸洗处理能降低研究材料在冷却液中的静态腐蚀速率。

2219铝合金变厚度板坯充液拉深工艺研究

针对运载火箭燃料贮箱整体箱底采用厚板旋压、再机械加工的方法存在的易开裂、加工量大的问题,提出了先机械加工获得变厚度板坯,再拉深成形的制造方法。圆形变厚度板坯具有中间薄、外缘厚的形状特点,成形中存在薄区易开裂的问题,为此采用充液拉深并结合弹性垫板的成形方法。通过数值模拟和工艺实验,研究液压和弹性垫板对变厚度板坯拉深成形壁厚及应变分布的影响规律。研究结果表明,增大液压和设置弹性辅助板能够增大界面摩擦,降低拉深试件的最大壁厚减薄率,改善薄区的壁厚分布。当液压为5.2 MPa、弹性辅助板厚度为5 mm时,试件最大壁厚减薄率为8.8%,相较于普通拉深降低34%。