表面硅烷改性和激光加工微倒钩结构对铝合金-CFRP胶接接头性能的影响 下载: 508次
The accelerated advancement of contemporary society has augmented the demand for diverse material properties, including but not limited to, fatigue properties, strength, and damage resistance, in aerospace, transportation, and navigation domains. However, conventional metallic materials, such as aluminum and titanium alloys, cannot always fulfill the high-performance frame member prerequisites specified in the aforementioned sectors. Carbon fiber-reinforced plastics (CFRP), a novel material renowned for its high-performance attributes, presents a promising potential for employment in the mentioned fields. Hence, the association of CFRP with metals is an inescapable prospect. As a connection method with a simple structure and low cost, adhesive joints have special advantages such as smooth adhesive joints, good sealing, and uniform stress distribution. The pretreatment of the bonding interface had a significant influence on joint strength. Laser processing offers significant advantages due to its environmental friendliness, high repeatability and stability, and excellent surface modification ability. Prior research has shown that laser surface treatment and chemical surface modification can enhance the strength of joints between CFRP and aluminum alloy. However, there have been limited studies on the strength changes of adhesively bonded joints between CFRP and aluminum alloy under the combined influence of both treatment methods. Therefore, this study employs a laser step scanning method to create a barb array on the surfaces of both the aluminum alloy and CFRP, and then investigates the effects of the barb array structure and silane coupling agent on the strength and failure mode of the adhesively bonded joint between the two materials.
The objective of this experiment is to compare the changes in the bonding strength of the aluminum alloy and CFRP surfaces resulting from different treatment methods. Three surface treatment methods are employed: first, the surfaces of the aluminum alloy and CFRP are ground using sandpaper to increase surface roughness. Second, a barb array structure is prepared on the aluminum alloy and CFRP surfaces using a laser step-scanning method. Third, the silane coupling agent is used for surface modification. The treated CFRP and aluminum alloy surfaces are bonded together, and the tensile strength of the adhesive joint is tested using an electronic universal tester. In addition, the X-ray photoelectron spectroscopy (XPS) is employed to test the surface chemical bonds after the silane treatment.
The laser step scanning method is used to prepare a barb array with good morphology (Fig. 4). The orientation of the barb structure on the aluminum alloy surface is found to be highly uniform. In addition, the surface of the gradual slope features independent spiky structures, which can effectively increase the contact area between the adhesive and aluminum alloy, thus, enhancing the bonding strength. Both the aluminum alloy and CFRP barb arrays demonstrate better interlocking effects (Fig. 5). An aluminum alloy barb array can be embedded in a CFRP to enhance mechanical interlocking. Upon applying a tensile load, the structure of the joint exhibits enhanced tensile strength. The XPS is employed to investigate the chemical bonding components at the interface between the aluminum alloy and CFRP, which has been modified by the silane coupling agent. Following the silane treatment, a novel Si—O—Al chemical bond emerges on the surface of the aluminum alloy, and a silane transition layer is formed between the aluminum alloy and adhesive (Fig. 6). Compared to sandpaper, the strength after laser treatment increases by 24.6% to 16.7 MPa. After the silane modification, the strength increases slightly, reaching 17.4 MPa (Fig. 7). After the silane modification, the adhesive effect on the aluminum alloy surface is further enhanced, resulting in the appearance of carbon fiber tear failures (CFTs) and an overall improvement in the joint strength. However, the proportion of such carbon fiber tear failures is relatively low after silane modification, thus limiting the strength enhancement (Fig. 8).
The laser step-scanning method can form a regular barb array on aluminum alloy and CFRP surfaces and mesh perfectly. The utilization of this structure can significantly enhance the joint strength, resulting in the formation of a high-strength and highly stable adhesive joint. The XPS analysis confirms that the surface of the aluminum alloy can be effectively modified by a silane coupling agent, forming an Al—O—Si bond at the surface, which verifies the formation of a silane transition layer between the adhesive and the aluminum alloy interface following the surface modification. This not only leads to an enhancement of the joint strength, but also increases its stability. The fracture diagram shows that with an increase in joint strength, cohesion failure begins to occur on a large scale. Simultaneously, owing to the further increase in the bond strength after treatment with the silane coupling agent, a small part of the carbon fiber surface is torn, and carbon fiber tear failures begin to occur at the fracture.
The three aforementioned experimental outcomes suggest that silane modification and laser texturing can effectively enhance joint strength and form a high-strength adhesive joint, thereby strengthening the vulnerable connection between CFRP and aluminum alloy composite structural parts. This improvement significantly enhances the overall strength of composite structural parts and makes them more suitable for lightweight applications that use CFRP.
1 引言
随着现代社会的高速发展,航空航天、交通和航海等领域对材料的各种性能如疲劳性能、强度、抗损伤性能的要求越来越高。然而,单一的传统金属材料如铝合金、钛合金等无法满足这些要求。碳纤维增强塑料(CFRP)作为一种新型材料,具有重量轻、强度高、耐疲劳、耐腐蚀等优异性能,因此得到越来越广泛的应用。虽然CFRP的性能优异,但是在大型结构件中CFRP无法完全取代各种金属,因此,CFRP与金属的连接是不可避免的[1-2]。传统的异种材料连接技术存在应力集中、部件过重等问题,而且钻孔操作会对连接件造成损伤[3-5]。胶接作为一种简单且成本较低的连接方法,不仅可以避免传统连接方式带来的问题,同时胶接机制具有特殊的优势,例如胶接接头平整,密封性、绝缘性、防腐性优异,胶接接头的应力承载面积较大,因此接头的应力分布均匀,不易产生应力集中等[6]。
胶接界面预处理对接头强度有着很大影响,表面处理可以有效去除CFRP与金属表面残留的颗粒污染物和油污,同时还能改变黏结表面的物理化学特性。目前,常用的金属表面处理工艺可分为两类。一种是通过机械处理增加表面粗糙度,研究表明,铝合金的表面湿润性越好,黏结剂越容易在表面铺展[7-8]。同时,机械处理会在铝合金表面形成不规则微结构,黏结剂流入其中会形成机械黏合,从而增强黏结强度,例如砂纸打磨、喷砂等方法[9-10]。另一种是化学处理的方法,这种方法一方面可使黏结界面脱脂,另一方面化学腐蚀可以去除表面氧化层,并在黏结表面形成微纹理结构,也会使黏结强度提升[11]。激光加工在环境保护、重复性、稳定性和表面改性方面具有显著优势,兼具机械表面处理和化学表面处理方法的优点,有望在未来成为有效的替代方法[12-14]。
基于以上特点,国内外学者展开了很多研究。邹田春等[15]研究了不同搭接长度对CFRP单搭接接头的拉伸性能及失效特征的影响,结果表明:随着搭接长度的增加,接头平均剪切强度先降低后趋于稳定,同时接头失效特征由剪切力主导向剥离力主导转变。杜婷婷等[16]研究了纳秒激光表面处理对CFRP表面润湿性和胶接性能的影响,结果表明:与未处理的CFRP相比,激光处理后的CFRP表面粗糙度和润湿性明显增加,同时胶接强度提升了129.41%。刘一凡等[17]研究了表面变宽度网格微织构对TC4与CFRP激光连接工艺以及连接界面的强化机理,结果表明:随着微织构宽度的增大,CFRP在TC4表面的接触情况由不润湿变成润湿,表面微织构显著提高了TC4表面对熔化CFRP的吸附能力,促进了界面的机械嵌合作用。微织构能增加界面接触面积并实现表面改性,促进CFRP与TC4在高温下发生化学连接,从而进一步提高接头强度。Özgür等[18]研究了不同浓度的硅烷偶联剂下CFRP胶接接头强度的变化,结果表明:在硅烷偶联剂体积分数为3%的情况下,黏结强度达到17.27 MPa,并且在铝合金表面检测到了硅氧烷基团,这被认为是铝合金与环氧树脂之间形成了化学键。Xie等[19]采用两步激光表面处理的方法改善CFRP单搭接接头的性能,结果表明:利用激光雕刻交叉沟槽结构可以有效提升连接强度,并且碳纤维的径向与轴向热导率是不同的,这导致不同方向上的激光扫描效果不一致。
在已知的研究中,激光表面处理和化学表面改性的方法都可以提升CFRP与铝合金接头的强度,但是目前国内外关于二者共同作用下CFRP与铝合金胶接接头的强度变化研究鲜有报道。因此,本文将激光表面处理和化学表面处理的方法结合起来,通过激光阶梯扫描的方法在铝合金与CFRP表面上制备了倒钩阵列,并研究了倒钩阵列结构和硅烷偶联剂共同作用下铝合金与CFRP胶接接头的强度和失效类型。通过X射线光电子能谱(XPS)方法分析了硅烷偶联剂表面改性后胶接界面的成分变化。
2 实验材料与方法
2.1 实验材料与设备
本实验选用铝合金与碳纤维增强塑料作为黏结材料。铝合金尺寸为25 mm
在本实验中铝合金与CFRP都需要进行表面处理,为了使结构可以更好啮合,使用同一台激光器进行处理。所用激光器的波长为1064 nm,最大输出功率为30 W,脉冲宽度为10 ps,重复频率可在50 kHz~1 MHz范围内调节。激光器及光路示意图如
图 1. 激光器及光路示意图。(a)激光器实物图;(b)激光器光路示意图
Fig. 1. Schematics of laser and optical path. (a) Physical picture of laser; (b) schematic of laser optical path
2.2 实验过程
2.2.1 表面处理方法
本实验的目的是比较铝合金与CFRP表面经过不同方法处理后接头强度的变化,因此表面处理方法主要是以下三种:
第一种方法是利用砂纸对铝合金与CFRP表面进行打磨,增加表面粗糙度。砂纸打磨后在丙酮中对样品进行10 min的超声清洗,待样品自然干燥后进行下一步黏结操作。
第二种方法是用激光阶梯扫描的方法在铝合金与CFRP表面上制备出倒钩阵列结构,具体方法如
图 2. 倒钩阵列参数及制作过程示意图。(a)倒钩阵列结构;(b)倒钩阵列参数示意图;(c)倒钩阵列制作过程示意图
Fig. 2. Schematics of barb array parameters and fabrication process. (a) Structure of barb array; (b) schematic of barb array parameters; (c) schematics of barb array fabrication process
表 2. 制作铝合金与CFRP表面倒钩阵列所使用的激光参数
Table 2. Laser parameters used to produce barb arrays on aluminum and CFRP surfaces
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第三种表面处理方法为硅烷偶联剂表面改性法。该方法是在经过激光处理并超声清洗后的铝合金表面上均匀涂抹硅烷偶联剂,再放入干燥箱中干燥,然后进行下一步黏结操作。
2.2.2 黏结方法
用胶枪在经三种方法处理后的铝合金与CFRP样品表面涂抹黏结剂,通过按压的方法将铝合金与CFRP搭接在一起,并使倒钩结构正确啮合。通过特制夹具给铝合金与CFRP接头施加0.3 MPa的压力,压力值的大小通过定力矩扳手调节。接头制作完成后在常温下固化24 h,并在两端贴上垫片以平衡施加拉伸载荷时产生的力矩,制作CFRP铝合金胶接接头的过程示意图如
图 3. 胶接过程示意图。(a)激光处理;(b)涂抹硅烷偶联剂;(c)涂抹黏结剂;(d)加压粘结;(e)添加垫片
Fig. 3. Schematics of gluing process. (a) Laser treatment; (b) application of silane coupling agent; (c) application of adhesive; (d) pressurized bonding; (e) addition of gaskets
3 结果与讨论
3.1 倒钩结构的制作与啮合效果
3.1.1 铝合金与CFRP表面处理后的形貌
图 4. 倒钩阵列结构的3D形貌图。(a)铝合金表面倒钩结构的宏观3D形貌图;(b)CFRP表面倒钩结构的宏观3D形貌图;(c)铝合金倒钩结构的微观3D形貌图;(d)CFRP倒钩结构的微观3D形貌图
Fig. 4. 3D morphologies of barb array structure. (a) Macroscopic 3D morphology of barb structure on aluminum alloy surface; (b) macroscopic 3D morphology of barb structure on CFRP surface; (c) 3D microstructure of aluminum alloy barb structure; (d) 3D microstructure of CFRP barb structure
3.1.2 铝合金与CFRP表面倒钩啮合效果
图 5. 胶接接头截面图。(a)倒钩阵列接头的截面;(b)砂纸粗化处理后接头的截面;(c)未处理接头的截面
Fig. 5. Cross-sectional views of adhesive joint. (a) Cross section of barb array joint; (b) cross section of joint after sandpaper roughening; (c) cross section of untreated joint
3.2 断口失效分析
3.2.1 胶接界面XPS分析
利用XPS研究了硅烷偶联剂表面改性后铝合金与CFRP结合界面的化学键成分。
图 6. 铝合金断口的XPS图。未经硅烷偶联剂改性的(a)Al2p和(b)O1s光谱;经硅烷偶联剂改性后的(c)Al2p和(d)O1s光谱
Fig. 6. XPS images of fracture interface of aluminum alloy. (a) Al2p and (b) O1s spectra without silane coupling agent modification; (c) Al2p and (d) O1s spectra after silane coupling agent modification
3.2.2 接头拉伸剪切强度
式中
3.2.3 断口失效类型分析
本实验所涉及的失效类型共分为三种。第一种是黏附失效(简称AF)。黏附失效是指失效发生在金属与黏结剂之间或黏结剂与CFRP之间,且黏结剂在金属或CFRP表面没有残留,这种失效模式对应于最弱的结合强度,需要避免。第二种失效是内聚失效(简称CF)。内聚失效是指黏结剂内部发生的失效,即在金属与CFRP的表面都保留有一层黏结剂。许多研究表明,从黏附失效转变为内聚失效可以极大地提高黏结强度。如果CFRP部分碳纤维被拔出并残留在金属表面上,这种失效形式是碳纤维撕裂失效(简称CFT)。
图 8. 不同处理方法下胶接接头的断口图。(a)未处理;(b)砂纸打磨处理;(c)只进行激光处理;(d)经过硅烷偶联剂改性和激光处理
Fig. 8. Fracture diagrams of adhesive joints under different treatment methods. (a) No treatment; (b) sandpaper treatment; (c) only laser treatment; (d) silane coupling agent modification and laser treatment
4 结论
通过激光阶梯扫描的方法在铝合金与CFRP表面制作了相互啮合的倒钩阵列。观察了倒钩阵列的制备效果和啮合效果,测试了不同表面处理方式对胶接接头拉伸强度的影响,分析了硅烷偶联剂改性处理后表面的成分变化,得到如下结论:
第一,激光阶梯扫描的方法可以在铝合金与CFRP表面形成规则的倒钩阵列,并且啮合完美。这种结构使铝合金与CFRP黏结界面之间的机械互锁效应大幅提升,形成高强度高稳定的胶接接头。
第二,对改性后的铝合金表面进行XPS分析,结果表明,硅烷偶联剂可以成功改性铝合金表面,在铝合金表面形成Al—O—Si键,这证明了硅烷偶联剂表面改性后会在黏结剂与铝合金连接界面之间形成硅烷过渡层,这是胶接接头强度进一步提升的主要原因,同时黏结界面间的硅烷过渡层也增加了接头的稳定性。
第三,接头断口图像显示,随着接头强度的增加,内聚失效开始大规模出现,同时由于硅烷偶联剂改性处理后黏结强度进一步提升,因此少部分的表层碳纤维被撕裂,断口开始出现碳纤维撕裂失效。
以上结果显示:在硅烷改性和激光织构共同作用下,接头强度明显提升,同时接头稳定性也有所提升,形成高强度胶接接头。这可以使CFRP与铝合金复合结构件的整体强度大幅提升,有利于CFRP轻量化应用。
[1] Li H G, Xu Y W, Hua X G, et al. Bending failure mechanism and flexural properties of GLARE laminates with different stacking sequences[J]. Composite Structures, 2018, 187: 354-363.
[2] 景若木, 徐洁洁, 肖荣诗, 等. 碳纤维增强复合材料与钛合金激光连接仿真[J]. 中国激光, 2023, 50(8): 0802014.
Jing R M, Xu J J, Xiao R S, et al. Simulation study of laser joining of carbon fiber reinforced plastics and titanium alloy[J]. Chinese Journal of Lasers, 2023, 50(8): 0802014.
[3] 杜力松, 黄亚新, 张釜恺. CFRP-铝合金层合板螺栓连接失效仿真及实验研究[J]. 装备制造技术, 2021(11): 76-84, 91.
Du L S, Huang Y X, Zhang F K. Simulation and experimental study on bolt connection failure of CFRP-aluminium alloy laminates[J]. Equipment Manufacturing Technology, 2021(11): 76-84, 91.
[4] Qiu X Y, Li P N, Li C P, et al. Study on chisel edge drilling behavior and step drill structure on delamination in drilling CFRP[J]. Composite Structures, 2018, 203: 404-413.
[5] 邱建平, 陈金祥, 周莹, 等. CFRP/Ti叠层构件螺旋铣孔层间孔径偏差研究[J]. 航空制造技术, 2023, 66(9): 93-98,111.
Qiu J P, Chen J X, Zhou Y, et al. Research on hole diameter deviation between layers in helical milling of CFRP/Ti stacks[J]. 航空制造技术, 2023, 66(9): 93-98,111.
[6] Garcia R, Prabhakar P. Bond interface design for single lap joints using polymeric additive manufacturing[J]. Composite Structures, 2017, 176: 547-555.
[7] Yan Y T, Liu B S, Xu T X, et al. Realizing the air brazing of ZrO2 ceramics through Al metal[J]. Journal of Materiomics, 2022, 8(3): 662-668.
[8] Persson B N J, Liu B S, Xu T X, et al. Relation between interfacial separation and load: a general theory of contact mechanics[J]. Physical Review Letters, 2007, 99(12): 125502.
[9] 胡伟, 蔡如琳, 谭利敏, 等. 几种机械表面处理方法对6013铝合金接头胶接性能的影响[J]. 粘接, 2014, 35(1): 45-49.
Hu W, Cai R L, Tan L M, et al. Effect of mechanical surface treatments on bonding property to 6013 aluminum alloy[J]. Adhesion, 2014, 35(1): 45-49.
[10] Mousa S, Kim G Y. A direct adhesion of metal-polymer-metal sandwich composites by warm roll bonding[J]. Journal of Materials Processing Technology, 2017, 239: 133-139.
[11] 邹田春, 刘志浩, 李晔, 等. 等离子体表面处理对碳纤维增强树脂基复合材料(CFRP)胶接性能及表面特性的影响[J]. 中国表面工程, 2022, 35(1): 125-134.
Zou T C, Liu Z H, Li Y, et al. Effect of plasma surface treatment on bonding properties and surface properties of CFRP[J]. China Surface Engineering, 2022, 35(1): 125-134.
[12] 苏飞, 李文毅, 李纯杰. 纤维增强复合材料激光加工研究进展[J]. 宇航材料工艺, 2021, 51(6): 1-9.
Su F, Li W Y, Li C J. Research on laser processing of fiber reinforced plastics[J]. Aerospace Materials & Technology, 2021, 51(6): 1-9.
[13] Zhang Z, Shan J G, Tan X H, et al. Improvement of the laser joining of CFRP and aluminum via laser pre-treatment[J]. The International Journal of Advanced Manufacturing Technology, 2017, 90(9): 3465-3472.
[14] 陈亚军, 鲁文婷, 杨雅婷. 基于响应面分析的碳纤维复合材料基激光除漆工艺优化[J]. 中国激光, 2023, 50(12): 1202005.
Chen Y J, Lu W T, Yang Y T. Optimization of laser paint removal process for carbon fiber composite substrates based on response surface analysis[J]. Chinese Journal of Lasers, 2023, 50(12): 1202005.
[15] 邹田春, 符记, 李龙辉, 等. 搭接长度对CFRP单搭接胶接接头拉伸性能及破坏特征的影响[J]. 材料工程, 2021, 49(7): 158-165.
Zou T C, Fu J, Li L H, et al. Effect of overlap length on tensile properties and failure characteristics of CFRP single-lap adhesive joints[J]. Journal of Materials Engineering, 2021, 49(7): 158-165.
[16] 杜婷婷, 叶云霞, 刘远方, 等. 纳秒激光调控CFRP复合材料表面润湿性及其对胶接性能的影响[J]. 复合材料学报, 2021, 38(5): 1435-1445.
Du T T, Ye Y X, Liu Y F, et al. Tailoring CFRP composite surface wettability with nanosecond laser and its effect on bonding performance[J]. Acta Materiae Compositae Sinica, 2021, 38(5): 1435-1445.
[17] 刘一凡, 周宝升, 张涛, 等. 基于表面微织构的钛合金与CFRP激光连接研究[J]. 中国激光, 2022, 49(18): 1803001.
[18] Özgür Bora M, Çoban O, Akman E, et al. Comparison of novel surface treatments of Al2024 alloy for al/cfrp adhesive bonded joints[J]. International Journal of Adhesion and Adhesives, 2020, 103: 102721.
[19] Xie Y X, Yang B B, Lu L S, et al. Shear strength of bonded joints of carbon fiber reinforced plastic (CFRP) laminates enhanced by a two-step laser surface treatment[J]. Composite Structures, 2020, 232: 111559.
[20] Zhou X K, Xue W, Liu W W, et al. Quadri-directionally anisotropic droplets sliding surfaces fabricated by selective laser texturing of aluminum alloy plates[J]. Applied Surface Science, 2020, 509: 145406.
[21] Herzog D, Jaeschke P, Meier O, et al. Investigations on the thermal effect caused by laser cutting with respect to static strength of CFRP[J]. International Journal of Machine Tools and Manufacture, 2008, 48(12/13): 1464-1473.
[22] Lin W C, Li X P, Dong W P, et al. Ultrahigh bonding strength and excellent corrosion resistance of Al-TPU hybrid induced by microstructures and silane layer[J]. Journal of Materials Processing Technology, 2021, 296: 117180.
[23] Zhu W, Xiao H, Wang J, et al. Characterization and properties of AA6061-based fiber metal laminates with different aluminum-surface pretreatments[J]. Composite Structures, 2019, 227: 111321.
[24] Reitz V, Meinhard D, Ruck S, et al. A comparison of IR- and UV-laser pretreatment to increase the bonding strength of adhesively joined aluminum/CFRP components[J]. Composites Part A: Applied Science and Manufacturing, 2017, 96: 18-27.
[25] Harder S, Schmutzler H, Hergoss P, et al. Effect of infrared laser surface treatment on the morphology and adhesive properties of scarfed CFRP surfaces[J]. Composites Part A: Applied Science and Manufacturing, 2019, 121: 299-307.
Article Outline
张书平, 曹宇, 杨文峰, 蔡燕, 刘文文, 朱德华, 张还. 表面硅烷改性和激光加工微倒钩结构对铝合金-CFRP胶接接头性能的影响[J]. 中国激光, 2023, 50(12): 1202203. Shuping Zhang, Yu Cao, Wenfeng Yang, Yan Cai, Wenwen Liu, Dehua Zhu, Huan Zhang. Effects of Surface Silane Modification and Laser Machining Microbarb Structure on Performance of Aluminum Alloy-CFRP Adhesive Joint[J]. Chinese Journal of Lasers, 2023, 50(12): 1202203.