Effect of Surface Texture on the Adhesion Performance of Laser Treated Ti6Al4V Alloy

The growing demand in lighter and safer structures generates the requirement of lighter joining strategies, particularly for lightweight metal alloys, composites, and also joining dissimilar materials together. Titanium alloys stand out as the conventional choice for materials for light weight structures. Adhesive bonding of titanium is an appealing route for joint design, also for the possibility of joining it with dissimilar materials. The realization of a strong joint depends not only on the joint design and type of adhesive, but also on the preparation of the adhering surface. Laser texturing presents advantages compared to common surface preparation processes in terms of eco-compatibility, energetic efficiency, ease of manufacturing, and repeatability. This work presents a preliminary investigation on laser texturing of Ti6Al4 V alloy with a pulsed fiber laser source with the aim to increase surface adhesion for bonding. Particularly, different surface textures are proposed, and laser machining strategies are developed. The results showed that laser texturing provided up to eightfold and 30% higher shear strength compared to plain and sand blasted surfaces, respectively. Failure analysis showed that a margin of improvement is still possible by adapting the surface texture for better cavity filling and reducing surface damage caused by the laser treatment.     

Electrodeposition of organofunctional silanes and its influence on structural adhesive bonding

Four different organofunctional silanes were selected and deposited on chemically pretreated aluminum surfaces by immersion and electrodeposition techniques. The surface morphology, comparison of elemental constituents, and surface free energies of silane-coated aluminum were investigated by low voltage scanning electron microscopy (LVSEM), low voltage X-ray analysis (LVXA), and contact angle measurement, respectively. The initial bond strength and long-term durability were evaluated with epoxy adhesive by lap shear tests. The deposition of silane coupling agents enhanced the bond durability of aluminum/epoxy joints under heat and humidity conditions. Also the performance of silane coupling agents depended on the application method. The electrodeposition technique produced a more uniform coverage of silane on the aluminum surface and, thus, was generally more effective than the immersion technique in improving bond performance.     

Optimization of weld bonding process parameters of austenitic stainless steel 304L and low carbon steel sheet dissimilar joints

Weld bonding is a hybrid joining process used to produce weld joints between similar or dissimilar metallic materials. In this work, a systematic study has been undertaken to investigate the effect of the input process parameters on the weld joint quality of dissimilar materials i.e. austenitic stainless steel 304L and low carbon steel sheet, in terms of joint strength. Experiments were planned on the basis of response surface methodology technique with three control factor and their three levels of process parameters. Experimental results were used to develop a mathematical model to predict the tensile shear strength and peel strength of the weld joint. A mathematical model, correlating the process parameters and their interaction on responses, was also established. The developed model was validated with the confirmation test case experiment, and it has been observed that the developed model is capable to evaluate weld joint strength within the range of process parameters being used. Numerical optimization technique was applied to find out the optimal set of input parameters.     

Durability of Adhesive Bonds to Zinc-Coated Steels: Effects of Corrosive Environments on Lap Shear Strength

The effects of corrosive environments on adhesive bonds to electro-galvanized, zinc/aluminum alloy coated, coated electro-galvanized, and cold-rolled steels have been investigated. Bonds prepared using a rubber-modified dicyandiamide-cured epoxy adhesive, an epoxy-modified poly(vinyl chloride)-based adhesive, an acrylic-modified poly(vinyl chloride)-based adhesive a one-part urethane adhesive, and a two-component epoxy-modified acrylic adhesive were exposed under no-load conditions to constant high humidity or cyclic corrosion exposure for 50 days or 50 cycles (10 weeks) respectively.

Over the course of this study, exposure to constant high humidity had little effect on lap shear strength for any of the systems studied. Bond failures were initially cohesive, and with few exceptions remained so.

Bond strength retention under the cyclic corrosion exposure conditions employed was strongly dependent on adhesive composition and on substrate type. On galvanized substrates, lap shear strengths for the poly(vinyl chloride)-based adhesives were reduced by 90-100% during the course of the corrosion exposure, and a change in the mode of bond failure (from cohesive to interfacial) was observed. On the coated electro-galvanized steel substrate, the poly(vinyl chloride)-based adhesives showed about 50% retention in lap shear strength and a cohesive failure throughout most of the corrosion test. The dicyandiamide-cured epoxy adhesive used in this study generally showed the best lap shear strength retention to zinc-coated substrates; bonds to cold-rolled steel were severely degraded by corrosion exposure. The performance of the acrylic and urethane adhesives were intermediate to the dicyandiamide-cured epoxy and poly(vinyl chloride)-based adhesives in strength retention.     

Durability of Adhesive Bonds to Zinc-Coated Steels: Effects of Corrosive Environments on Lap Shear Strength

The effects of corrosive environments on adhesive bonds to electro-galvanized, zinc/aluminum alloy coated, coated electro-galvanized, and cold-rolled steels have been investigated. Bonds prepared using a rubber-modified dicyandiamide-cured epoxy adhesive, an epoxy-modified poly(vinyl chloride)-based adhesive, an acrylic-modified poly(vinyl chloride)-based adhesive a one-part urethane adhesive, and a two-component epoxy-modified acrylic adhesive were exposed under no-load conditions to constant high humidity or cyclic corrosion exposure for 50 days or 50 cycles (10 weeks) respectively.

Over the course of this study, exposure to constant high humidity had little effect on lap shear strength for any of the systems studied. Bond failures were initially cohesive, and with few exceptions remained so.

Bond strength retention under the cyclic corrosion exposure conditions employed was strongly dependent on adhesive composition and on substrate type. On galvanized substrates, lap shear strengths for the poly(vinyl chloride)-based adhesives were reduced by 90–100% during the course of the corrosion exposure, and a change in the mode of bond failure (from cohesive to interfacial) was observed. On the coated electro-galvanized steel substrate, the poly(vinyl chloride)-based adhesives showed about 50% retention in lap shear strength and a cohesive failure throughout most of the corrosion test. The dicyandiamide-cured epoxy adhesive used in this study generally showed the best lap shear strength retention to zinc-coated substrates; bonds to cold-rolled steel were severely degraded by corrosion exposure. The performance of the acrylic and urethane adhesives were intermediate to the dicyandiamide-cured epoxy and poly(vinyl chloride)-based adhesives in strength retention.     

NOTE The Application of Surface Analysis Techniques in the Adhesive Bonding of Oily Automotive Steel

There are fewer papers on the adhesive bonding of steel for structural applications than for aluminum and titanium alloys. However, the approach to the adhesive bonding of all three adherends has been similar, that is, the surfaces are pretreated prior to bonding. Trawinski, et al.^1,2,3 reviewed several conversion coatings or etching processes used for steel. Haak and Smith⁴ selected two surface treatments among nineteen based on minimal cost, simplicity and good durability. Smith⁵ has reported work on stainless steel-epoxy bonds under hydrothermal stress. Bischof, et al.⁶ investigated the effect of surface pretreatment of steel on bonding strength obtained with polyvinyl chloride. Ziane, et al.⁷ identified four fracture zones resulting from shear loading of epoxy bonded galvanized steel following four different surface pretreatments. But in some cases, as in the automotive industry, there is a need to bond oily steel directly without surface pretreatment. Rosty, et al.⁸ have reported a study of the role of fillers and cure temperature on the shear strength of oily steel bonded with epoxy. None of the reported research utilizes both microscopic and spectroscopic techniques to analyze the fracture surfaces.     

Failure analysis of AA8011-pultruded GFRP adhesively bonded similar and dissimilar joints

In this work, a comparative failure analysis of aluminum (AA8011/AA8011) and glass fiber reinforced polyester (GFRP/GFRP) based similar and dissimilar joints is presented. The GFRP is prepared using pultrusion technique. Single lap joints are prepared by using Araldite R2011 epoxy as an adhesive. The lap joints are then tested under tension to estimate the average shear strength of the assembly. It is observed that the average bond strength of AA8011/AA8011 is lesser than that of the GFRP/GFRP joint. The failure of similar joints occurred by fracture within the adhesive. The dissimilar joint is failed predominantly by interface debonding. Further, a detailed three dimensional stress analysis of the joints is carried out using finite element method (FEM). The damage analysis of adhesive layer is carried out by coupling FEM with cohesive zone model (CZM). The stress, damage distributions and failure mechanisms are compared for similar joints in detail. A failure mechanism is proposed for AA8011/AA8011 type joint that favours a rapid crack growth in the adhesive after crack initiation, which is responsible for lesser bond strength. The increase in overlap length has positive effect that the peak load increases proportionally with overlap length.     

The effect of polymer network structure upon the bond strength of epoxy–aluminum joints

The bond strength to aluminum of Epon 828 cured with various amounts of methylene dianiline has been investigated as a function of the resin network structure. In order to meet this objective, a torsional test for bond shear strength was developed, and fully cured resins with different network structures were prepared. The effects of the rate of loading of the joint and the aluminum surface pretreatment on the bond strength were also examined. Very high bond shear strengths, in excess of 9000 psi, were found for joints which after machining had been polished, vapor degreased, and treated with dilute sulfuric acid–potassium dichromate solution. It was found for these joints that the average bond strength decreased as the molecular weight between crosslinks increased. For the joints without acid–dichromate treatment, the failures were adhesive, and the network structure did not seem to significantly affect the bond strength. There are indications that chemical bonding occurred in the case of the acid–dichromatetreated joints; the decrease in bond strength as per cent excess amine and M_c increased is possibly associated with a decreased amount of chemical bonding. The bond strength increased to a limiting value as the rate of testing increased.     

Effect of surface exposure time on bonds to aluminum

Lap joints with AF-126 adhesive were prepared from surfaces of 2024-T3, 2024-T3 alclad, and 6061-T4 aluminum alloys treated by either FPL etch, sandblasting, or vapor degreasing. The strength data were described by a two-parameter Weibull distribution. Allowing between 1 hr and 30 days to elapse between surface preparation and actual bonding had no appreciable effect on bond strength. This was true for all three alloys surface treated in each of the three ways as well as for bonds either tested at ambient conditions or aged for 30 days at 120°F and 95% R.H. 2024-T3 aluminum, both bare and alclad, formed bonds that showed better strength than 6061-T4 aluminum.     

Dynamic strength of single lap joints with similar and dissimilar adherends

The increased use of adhesives for joining structural parts demands a thorough understanding of their load carrying capacity. The strength of the adhesive joints depends on several factors such as the joint geometry, adhesive type, adherend properties and also on the loading conditions. Particularly polymer based adhesives exhibit sensitivity to loading rate and therefore it is important to understand their behavior under impact like situations. The effect of similar versus dissimilar adherends on the dynamic strength of adhesive lap joints is addressed in this study. The dynamic strength is evaluated using the split-cylinder lap joint geometry in a split Hopkinson pressure bar setup. The commercial adhesive Araldite 2014 is used for preparing the joints. The adherend materials considered included steel and aluminum. The results of the study indicated that the dynamic strength of the lap joint is influenced by the adherend material and also by the adherent combination. Even in the case of joints with similar adherends, the strength was affected by the adherend type. The strength of steel–steel joints was higher than that for aluminum–aluminum joints. In the case of dissimilar adherends, the strength was lower than that of the case of similar adherends. The results of this study indicate that the combination of adherend material should also be accounted for while designing lap joints.     

Effects of a sheet metal stamping lubricant on static strength of adhesive-bonded aluminum alloys

Stamping lubricant is often applied to sheet metal surface to improve the formability. In this study, the effect of stamping lubricant on the strength of adhesive-bonded 1.0-mm-thick bare aluminum (Novelis X610-T4PD) and 0.9-mm-thick bare aluminum (Novelis X626-T4P) joints was investigated. It was found that while a proper amount of lubricant (~2.21 g/m², 1.5?μL lubricant on the 25?×?25 mm coupon) applied on the surface of the substrate had little effect on the joint strength, levels more than 2.21 g/m² lubricant significantly decreased the joint strength. When the lubricant amount exceeds the adhesive’s compatibility with the lubricant, the negative effects of pores from lubricant evaporation during curing on the strength overrides the positive effect of increased adhesion energy. Furthermore, the presence of 2.21 g/m² lubricant minimized the reduction of the strength of the joints pre-exposed to neutral salt spray (i.e. a concentration of 50?±?5 g/L sodium chloride solution). Careful analyses of the results indicated that corrosion of aluminum substrate surfaces of the pre-exposed joints led to the degradation in bond adhesion between the adhesive and substrates, and consequently resulted in the decrease of the joint strength. The hydrophobic lubricant protected the aluminum substrate from electrochemical reaction by damage of the bond adhesion between the adhesive and substrates leading to the lubricated joints having better corrosion resistance than the unlubricated joints.     

Effect of geometry and hybrid adhesive on strength of finger joints of Pinus elliottii subject to humidity and temperature

The optimized bonding of glued finger joints is required for structural and nonstructural applications. The use of nonspecific adhesives, combined with the joint geometry and exposure of joints to humidity and temperature, are factors that can compromise the durability of glued joints. The main objective of this study is the development of cross-linking poly(vinyl acetate) (PVAc) hybrid adhesive to produce nonstructural finger joints of Pinus elliottii with finger lengths of 6.5 and 4.5 mm. The adhesives were produced by emulsion copolymerization of vinyl acetate with n-butyl acrylate with different amounts of N-methylol acrylamide and blended with resorcinol-formaldehyde resin (RF) and aluminum chloride (AlCl₃). The rheological behavior of adhesives was investigated. We found that the joint configuration and the exposition time employed influenced joint strength. The PVAc/RF adhesive showed a thicker bond line and consequent deeper penetration into the pores of the wood as verified by microscopy analysis. Statistically differences in bond strength of the adhesive joints were found with respect to different conditioning times and finger length. The highest values were exhibited by the joints produced with a finger length of 6.5 mm and glued with the hybrid adhesive (AD-4) than that joints produced with a finger length of 4.5 mm.     

Rapid diffusion bonding of WC-Co cemented carbide to 40Cr steel with Ni interlayer: Effect of surface roughness and interlayer thickness

WC-Co cemented carbides were rapidly diffusion bonded to 40Cr steels with pure Ni as interlayers by utilizing plasma activated sintering (PAS). The bonding was carried out at 750 °C for 13 min under a pressure of 40 MPa. It was found that the roughness of the initial surfaces still plays an important effect on the microstructure and mechanical behavior of the joints diffusion bonded by PAS irrespective of the electric current applied during bonding. The adoption of smoother original surfaces was significantly favorable to eliminate the interfacial interstices and microvoids. Correspondingly, the shear strength of the diffusion bonded joints increased with decreasing surface roughness. Additionally, the effect of interlayer thickness on the shear strength of the joints was also evaluated, and the results showed that the strength decreased sharply when thicker interlayer was employed. A maximum value of shear strength, 293.07 MPa, was obtained when the original surfaces was ground with P1200 grit SiC paper and at the same time 50 µm thick interlayer was used. In this case, the fracture initiated and run predominantly along the bonding interfaces instead of in the WC-Co substrate.     

Mechanical behavior of polyurethane adhesive bonded joints as a function of temperature and humidity

The temperature and humidity were found to be the most effective parameters in the behavior of polyurethane flexible adhesive bonded aluminum joints. In order to obtain the effect of environment on bond strength, toughness, failure displacement, joints stiffness and failure model, in this work, aluminum single-lap joints were tested under various temperatures (25, 40, 60 and 80 °C) and relative humidity (RH, 55, 65, 75, 85, 95 and 99%) using an environmental chamber. The results showed that as the humidity increased from 55 to 99%, bond strength decreased as linear function. As the temperature increased from 25 to 80 °C, the bond strength decreased as exponential function. The joints stiffness reduced gradually with the increase of temperature and humidity. The analysis of the failure section of the ageing joints showed that the humidity caused the transition of the failure model, and the increase of the temperature promoted the change of the failure model. Besides, at low humidity (55 and 65%), failure displacement decreased gradually with the increase of temperature, and at high humidity (95 and 99%), failure displacement increased. This study will help engineers design a reliable, safe and effective bonding structure. And it is conducive to solve the problem of joint strength degradation in the hygrothermal environment.     

Nickel interlayer on the microstructure and property of TC6 to copper alloy diffusion bonding

In the present study, diffusion bonding of two dissimilar materials TC6 and copper alloy was investigated in vacuum chamber by directly bonding and using Ni foil as interlayer. Interface quality of the joints was evaluated by mechanical property and microstructure. The maximum shear strength of directly bonding was found to be 64 MPa for the speciemen bonded at 850 °C, 5 MPa for 30 min; and the maximum shear strength with Ni foil interlayer was 113 MPa under the same bonding parameters. The bonding interfaces and fracture surfaces were analyzed by energy disperse spectrometer, scanning electron microscopy and X-ray diffraction. The results show that the diffusion region of directly bonding specimen generated several IMCs (Ti₂Cu and Ti₅CuSn₃, etc.). Fracture morphology showed that brittle fracture present at the Ti₅CuSn₃ IMCs, which was the weak point of the joint. While the diffusion zone of the specimen with Ni foil interlayer consists of various phase including Ti₂Ni, TiNi, TiNi₃ at TC6 side, and Cu-Ni solid solution at ZQSn11-4-3 side, and fracture surface of joint present a mixture of brittle and ductile characteristics, and fracture initiated at the TiNi₃/Ni interface.     

Single and dual adhesive bond strength analysis of single lap joint between dissimilar adherends

The emerging trends for joining of aircraft structural parts made up of different materials are essential for structural optimization. Adhesively bonded joints are widely used in the aircraft structural constructions for joining of the similar and dissimilar materials. The bond strength mainly depends on the type of adhesive and its properties. Dual adhesive bonded single lap joint concept is preferred where there is large difference in properties of the two dissimilar adherends and demanding environmental conditions. In this work, Araldite-2015 ductile and AV138 brittle adhesives have been used separately between the dissimilar adherends such as, CFRP and aluminium adherends. In the dual adhesive case, the ductile adhesive Araldite-2015 has been used at the ends of the overlap because of high shear and peel strength, whereas in the middle of the bonded region the brittle adhesive AV138 has been used at different dimensions. The bond strength and corresponding failure patterns have been evaluated. The Digital Image Correlation (DIC) method has been used to monitor the relative displacements between the dissimilar adherends. Finite element analysis (FEA) has been carried-out using ABAQUS software. The variation of peel and shear stresses along the single and dual adhesive bond length have been captured. Comparison of experimental and numerical studies have been carried-out and the results of numerical values are closely matching with the experimental values. From the studies it is found that, the use of dual adhesive helps in increasing the bond strength.     

Stress analysis on a non-flat zigzag interface bonded joint

This article aims to explain the wide range of joint strengths observed depending on the nature of substrate surface geometry by linking the stress distributions in the adhesive layer to the overall strength of the adhesively bonded single lap joints (SLJs). The key factors to which the adhesion strength of non-flat interfaces is attributed are investigated numerically and experimentally. In an attempt to clarify the effect of mechanical interlock on overall adhesion strength of the adhesive joint, zigzag patterns were fabricated on the bonding surfaces of aluminum substrates. It was found that the local compressive and tensile stresses in the vicinity of the interface are the major cause of the practical enhancement or reduction of the joint strength. A comparison between the experimental results of optimum non-flat and standard SLJs showed a strength improvement of up to 40% compared to the conventional SLJ. According to the results of parametric studies, higher wave heights, lower wavelengths, and thinner bond lines improved the efficiency of the method.     

喷涂型汽车油箱点焊密封胶的研制

从油箱喷塑固化工艺条件出发,以环氧树脂(EP)和小分子聚酰胺为主要原料,制备了两种不同配方的汽车油箱用点焊密封胶。测试了点焊胶在90#汽油和0#柴油中的耐油性和粘接强度,并对三种不同连接接头(胶接、点焊、胶焊)的粘接强度进行了对比和分析。结果表明:点焊胶的固化工艺与汽车镀锌板类油箱表面漆层的固化工艺相同,故不必增加点焊胶的固化设备和工序;两种点焊胶具有较好的粘接性能,其T型剥离强度分别为89.0kN/m和92.0kN/m,拉伸剪切强度分别为13.3MPa和12.9MPa;两种点焊胶在90#汽油和0#柴油中浸泡360d后,试样的粘接强度降幅不明显,说明其具有一定程度的耐油性;将两种点焊胶用于汽车油箱的密封中,既具有良好的粘接密封性能,又解决了镀锌板类油箱渗漏油等问题。     

A study on the lap shear strength of a co-cured single lap joint

In this paper, the lap shear strength of a co-cured single lap joint subjected to a tensile load was investigated by experimental analysis. Co-cured joint specimens with several different bonding parameters such as bond length, surface roughness, and stacking sequence of the composite laminate were fabricated and tested. The dependence of the lap shear strength of the co-cured joint on the bonding parameters was investigated from the experimental results. The failure mechanism of the co-cured single lap joint was partially cohesive failure. The lap shear strength of the co-cured single lap joint was significantly affected by the bond length and the stacking sequence of the composite laminate. However, the effect of surface roughness on the lap shear strength of the co-cured single lap joint was not so significant.     

A design of experiments assessment of moisture content in uncured adhesive on static strength of adhesive-bonded galvanized SAE1006 steel

As part of a cooperative research program to develop and implement crash-resistant toughened adhesives targeted for future vehicles, this paper summarizes a study of the influence of pre-exposure of uncured adhesive and steel sheets in a humid and elevated temperature environment on quasi-static strength of bonded hot dipped galvanized SAE1006 steel joints.In this study, we use a DOE (design-of-experiment) program called DEXPERT to design the experiment and to analyze the effects of exposure temperature, exposure time, curing temperature and curing time on joint strength of adhesive-bonded galvanized SAE1006 steel. Prior to adhesive curing, the adhesive and galvanized steel coupons were pre-exposed to various relative humidity levels and temperatures. The experimental results were then analyzed by DEXPERT and the relative contributions of each factor on variance in joint strength were calculated. It was found that curing temperature is the most influential factor affecting the strength of adhesive-bonded galvanized SAE1006 steel joints. The curing of a joint at 180 °C can increase the robustness of the process and provides the greatest strength regardless of the variation of other factors. The joint strength curing at 150 °C shows a strong sensitivity to the curing time, while the adhesive cannot cure at 130 °C at all under all conditions. It has also been found that the pre-exposure of adhesive and steel for an hour can slightly decrease the joint strength at high temperature and humidity. Therefore, the effect of long time exposure of the uncured adhesive and steel still needs to be further investigated.