Preadhesion Laser Treatment of Aluminum Surfaces

An excimer laser may be used for preadhesion treatment of aluminum alloys. This method presents an alternative to the use of ecologically unfriendly chemicals involved in conventional anodizing pretreatments.

Experimental results indicate that preadhesion laser surface treatment significantly improved the shear strength of modified-epoxy bonded aluminum specimens compared with untreated and anodized substrates. The best results were obtained with laser energy of about 0.2 J/Pulse/cm² where single lap shear strength was improved by 600-700% compared with that of untreated Al alloy, and by 40% compared with chromic acid anodizing pretreatment.

The mode of failure changed from adhesive to cohesive as the number of laser pulses increased during treatment. The latter phenomenon has been correlated with morphology changes as revealed by electron microscopy, and chemical modification as indicated by Auger and infrared spectroscopy.

It can be concluded that the excimer laser has potential as a precise, clean and simple preadhesion treatment of Al alloys.     

Preadhesion Laser Surface Treatment of Carbon Fiber Reinforced PEEK Composite

An excimer UV laser (193 nm) was used for preadhesion surface treatment of PEEK (polyetheretherketone) composite. This method presented an alternative to other limited and polluting conventional surface treatment methods. Experimental results indicated that laser preadhesion treatment significantly improved the shear and tensile adhesion strength of structural epoxy FM 300 2K bonded PEEK composite adherends compared with untreated and SiC blasted substrates. Best results were obtained with laser energies of 0.18 or 1 J/P cm.² Shear strength of laser-treated joints was improved by 450% compared with that of untreated PEEK composite and by 200% compared with SiC-blasted pretreatment at ambient and at extreme temperatures. An order of magnitude of improvement was found in the tensile strength-of laser-treated PEEK composite in a sandwich structure compared with non-treated or abraded sandwich joints. The mode of failure changed from adhesive to cohesive as the number of pulses or laser energy increased during treatment. The latter phenomenon was correlated with surface cleaning as revealed by XPS, with morphology changes as revealed by scanning electron microscopy, and by chemical modification as indicated by FTIR and XPS. The bulk of the PEEK composite adherend was not damaged by the laser irradiation during treatment as indicated by the identical flexural strength before and after laser treatment. It can be concluded that the excimer laser has a potential as a precise, clean and simple preadhesion surface treatment for PEEK composite.     

Preadhesion laser surface treatment of polycarbonate and polyetherimide

The effects of carbon dioxide (10.6 μm) and argon fluoride excimer (193 nm) lasers as preadhesion surface treatments for polycarbonate and polyetherimide were studied. Single lap shear specimens bonded with a flexible polyurethane adhesive were utilized to investigate the effect of the various laser treatments on final shear properties and mode of failure. Experimental results based on mechanical properties, scanning electron microscopy and Fourier transform infra-red have indicated that the excimer laser is more effective than the carbon dioxide laser with respect to shear properties and the level of adhesion obtained with the thermoplastic adherends and polyurethane adhesive studied. Polycarbonate with its lower glass transition temperature T_g was affected by the carbon dioxide laser to a higher extent than the higher T_g polyetherimide. Furthermore, polycarbonate exhibited enhanced shear properties and a higher level of chemical modification following excimer laser irradiation compared to polyetherimide.     

Recent Trends in Surface Treatment Technologies for Airframe Adhesive Bonding Processing: A Review (1995–2008)

Proper surface treatment technologies are prerequisite for achieving long-term service capability through the adhesive bonding process. However, the current surface treatment technologies used in the adhesive bonding process for aluminum alloys depend on materials that are undesirable from an environmental- or safety perspective. Suitable alternatives in the aerospace industry are the subject of much interest: non-chromate anodizing, silane, sol-gel, laser, plasma, and ion beam enhanced deposition of Al₂O₃ film. These approaches can eliminate, or greatly reduce, the undesirable hazardous materials and have been proven to deliver comparable bonding performance. In some cases these alternative processes may even outperform established processes, such as chromic and phosphoric acid anodizing.     

阳极氧化对TC4钛合金力学与耐磨性能的影响

对比分析了脉冲阳极氧化和直流阳极氧化工艺对TC4钛合金表面形貌、拉伸性能、疲劳强度和耐磨性的影响。结果表明,脉冲阳极氧化和直流阳极氧化膜的粗糙度相较于TC4钛合金更大,而表面硬度从高至低为:脉冲阳极氧化膜>TC4钛合金>直流阳极氧化膜。虽然阳极氧化后试样的力学性能都相较于处理前有不同程度的减小,但是耐磨性有较大的提升。脉冲阳极氧化试样的疲劳强度接近TC4钛合金基材,且明显高于同样膜厚的直流阳极氧化试样,它的强度、断后伸长率和耐磨性也更优。     

Surface treatment of CFRP composites by Ar+ irradiation to improve bonding strength between aluminum and CFRP composites

The effect of surface treatment of carbon fiber reinforced plastic (CFRP) composites on the T-peel strength and the shear strength between CFRP and aluminum panels was studied. The surface of the composite panel was treated with Ar⁺ irradiation under oxygen environment. The optimal Ar⁺ ion dose was determined by measuring the changes of contact angle and surface energy as a function of ion dose. T-peel tests and SLS tests were performed using irradiated CFRP/aluminum specimens and unirradiated CFRP/aluminum specimens to determine the treatment effect by Ar⁺ irradiation under oxygen environment on the T-peel strength and shear strength of CFRP/aluminum composites. The results showed that contact angle on the surface of the composite panel was reduced from ∼80° to ∼8° and the surface energy increased from 31 ergs/cm² to 72.4 ergs/cm² with an ion dose of 10¹⁷ ions/cm². T-peel strength and shear strength are significantly affected by the surface treatment of composite panel. T-peel strength and shear strength improved 650% and 56%, respectively, when the treatment was made with an ion dose of 10¹⁶ ions/cm². SEM examination showed that the improvement of bonding strength was attributed to the uniform spread and fracture of epoxy adhesive.     

Effect of alkali treatment on properties of unidirectional isora fibre reinforced epoxy composites

Abstract

Unidirectional isora fibre reinforced epoxy composites were prepared by compression moulding. Isora is a natural bast fibre separated from Helicteres isora plant by retting process. The effect of alkali treatment on the properties of the fibre was studied by scanning electron microscopy (SEM), IR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mechanical properties such as tensile strength, Young's modulus, flexural strength, flexural modulus and impact strength of the composites containing untreated and alkali treated fibres have been studied as a function of fibre loading. The optimum fibre loading for tensile properties of the untreated fibre composite was found to be 49% by volume and for flexural properties the loading was optimised at ～45%. Impact strength of the composite increased with increase in fibre loading and remained constant at a fibre loading of 54·5%. Alkali treated fibre composite showed improved thermal and mechanical properties compared to untreated fibre composite. From dynamic mechanical analysis (DMA) studies it was observed that the alkali treated fibre composites have higher E' and low tan δ maximum values compared to untreated fibre composites. From swelling studies in methyl ethyl ketone it was observed that the mole percentage of uptake of the solvent by the treated fibre composites is less than that by the untreated fibre composites. From these results it can be concluded that in composites containing alkalised fibres there is enhanced interfacial adhesion between the fibre and the matrix leading to better properties, compared to untreated fibre composites.     

Shear strength of aluminum in shock waves

Two series of experiments are conducted for determining the shear strength of shockcompressed aluminum (type AD1) at pressures of 4–16 GPa, including in loading and release waves. A saturated water solution of ZnCl₂ serves as a control material. Previous data on the shear strength of materials based on measuring the two principal stresses are refined. It is confirmed that tangential stresses in aluminum and its alloys relax in the shock front for shock amplitudes exceeding 10 GPa. The reasons for discrepancies in previous determinations of the shear strength of metals in shock waves are clarified. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 102–107, January–February 1999.     

Photochemical surface modification of polypropylene for adhesion enhancement by using an excimer laser

Polypropylene (PP) surface in water was photochemically modified to render it hydrophilic using ArF excimer laser radiation. The chemical stability of PP is attributed to the C-H and C-H₃ bonds present. Thus, it is considered that H atoms are selectively pulled out from the area irradiated with ArF excimer laser light and are replaced with OH functional groups in the presence of water. In this treatment, the irradiated sample becomes hydrophilic with enhanced adhesion properties. The experimental conditions for this surface treatment were ArF laser fluence of 12.5 mJ/cm² and a shot number of 10000. The treated PP and stainless steel were bonded with epoxy adhesive and the tensile shear strength was 46 kg/cm².     

Polymerization of butadiene with tii4-Al(i-Bu)3 catalyst: Part I: Kinetic study

A kinetic study on the polymerization of butadiene in toluene with TiI₄-Al(i-Bu)₃ catalyst has been carried out in a batch reactor. The effects of catalyst concentration, Al/Ti ratio, initial monomer concentration and temperature on the polymerization rate and the molecular weight distribution were investigated. It was found that the rate of propagation which is first order with respect to monomer concentration is a function of Al/Ti ratio, having a maximum rate at a ratio of 1.5 and decreasing rapidly as ratio increases. The number of active sites which is directly proportional to the concentration of Til₄, is the prime determinant of the molecular weight of the polymer, yet the growth of the living polymer molecules is regulated by the chain transfer reaction to aluminum alkyls. The termination reaction was found significant only at Al/Ti ratio where the catalyst is most reactive.     

Al/PET adhesion: role of an excimer laser pretreatment of PET prior to aluminum thermal evaporation

The modifications induced on PET, poly(ethylene terephthalate), by an excimer laser irradiation performed below the polymer ablation threshold were studied. The laser treatment of the polymer before aluminum thermal evaporation improved the Al-PET adhesion. The enhancement of the metal-polymer interface strength is attributed to surface morphological changes rather than to chemical modifications of the PET surface. Surface oxidation under UV irradiation was found to degrade the adhesion.     

Microstructure Characterization of Laser Treated Surfaces

Excimer laser UV radiation presents a new technology for preadhesion surface treatment of various material adherends. The application of an ArF Excimer laser (193 nm) for surface pretreatment of polycarbonate, polyetherimide, PEEK composite, glass reinforced epoxy composite, aluminum, copper, magnesuim. PZT and fused silica was investigated. Experimental results indicated that UV laser surface treatment improved the adhesional strength significantly compared with conventionally-treated substrates for all the materials tested. The improved adhesion correlated with changes in morphology of the irradiated surface, chemical modification and removal of contaminants, which contributed to a strong and durable adhesive bond. This paper will concentrate only on the connection between the mechanical and morphological effect. The most common microstructure features on the surface after laser irradiation (examined by SEM and AFM) were small conical structures randomly distributed on the irradiated areas. Other features were periodic surface ridges or flat smoothened areas with spread arrays of microcracks. All these morphologies increase the roughness of the surface, enabling mechanical interlocking of the adhesive. It should be noted that the roughness is micronsized, and uniformly spread on the surface, which presents an advantage over abrasive treatments. The distribution of the features and their size were dependent on the laser parameters (intensity and number of pulses). Some mechanisms are presented, and these interesting phenomena are discussed.     

The adhesion of elastomer-coated glass fibers to an epoxy matrix. Part I: The effect of the surface treatments on the tensile strength of the glass fibers

E-glass fibers were subjected to various surface treatments to study the interfacial adhesion with an epoxy matrix by means of the fragmentation test. The glass fibers considered were both untreated and treated with γ-aminopropyltriethoxysilane (γ-APS). In addition, glass fibers were coated with a thin layer of a crosslinkable elastomer including (or not) a silane coupling agent. To evaluate the effect of the coating process, the glass fibers were also passed through the pure solvent (washed fibers). The tensile strength of glass fibers at short length (near the critical length, l_c, for the fragmentation test) cannot be measured directly, thus, extrapolation techniques were used. The Weibull statistics technique was applied and accurately described the tensile strength data of the tensile strength at various fiber gauge lengths for the different surface treatments. Nevertheless, the Weibull parameter, m, changes with the gauge length, and therefore, the extrapolation value at l_c depends on the method. The tensile strength of the silane-treated glass fibers is higher than for the untreated fibers, in agreement with reported data. This effect could be attributed to the protection against water provided by the silane sizing. The coating process does not induce any damage of the glass fibers since the washed fibers display mechanical properties close to those obtained for the untreated fibers. An additional effect is observed for the elastomer-coated fibers which present the highest tensile strength. This effect could be attributed to an improved protection and/or elimination of the weakest filaments in the glass strand during the treatment.     

Investigation on surface treatments of CFRP and aluminum to improve fracture toughness of adhesively-bonded CFRP–aluminum joints

In this study, the role of surface treatments of CFRP (graphite/epoxy composite) and aluminum (7075-T6) on the adhesively-bonded CFRP-aluminum joints has been investigated. The CFRP was surface-treated by Ar⁺ ion irradiation in an oxygen environment and the aluminum was surface-treated using a DC plasma. Ar⁺ ion irradiation treatment was carried out at Ar⁺ ion dose of 10¹⁶ ions/cm². Plasma treatment was carried out at a volume ratio of acetylene gas to nitrogen gas of 5:5 and the treatment time was 30 s. The effect of surface treatments on the fracture behavior CFRP-aluminum joints was determined from fracture tests using three different CLS (cracked lap shear) specimens: (1) untreated CFRP/untreated aluminum, (2) ion-irradiated CFRP/untreated aluminum and (3) untreated CFRP/plasma-treated aluminum. Fracture behaviors (fracture load, fracture toughness, fracture surfaces) of these three different specimens were compared. The results showed that both fracture load and fracture toughness of CFRP-aluminum joints were in the following order: ion-irradiated CFRP/untreated aluminum specimen > untreated CFRP/plasmatreated aluminum specimen > untreated CFRP/untreated aluminum specimen. SEM examination of fracture surfaces showed that fracture occurred as an interfacial failure for untreated specimens. On the other hand, a cohesive failure in the adhesive was the primary fracture mode for specimens surface-treated by ion irradiation or plasma.     

Effect of IR-laser treatment parameters on surface structure,roughness, wettability and bonding properties of fused deposition modeling-printed PEEK/CF

In this study, laser surface treatment was applied to alter the surface texturing and chemical compositions of fused deposition modeling (FDM)-printed PEEK/CF samples to improve the deficiency of inert surface of PEEK as adherend substrate. The influence of IR-laser parameters including treatment gaps, single pulse energy and pulse widths on surface properties and shear bond strength were discussed. The results indicated that surface roughness was enhanced with decreasing treatment gap or increasing pulse energy, which reached the highest value of Ra = 32.44 μm at 0.4*0.4 mm² treatment gap and 300 mJ single pulse energy. By adjusting laser pulse width, surface wettability changed from hydrophobicity to hydrophilicity. After micro-second laser ablation, the texturing structure was changed and acted as mechanical interlocking effect, and therefore make the shear bond strengths improve from 3.28 to 6.42 MPa compared with the untreated groups. On the other hand, functional groups on substrate surface were activated after nano-second laser ablation, which contributes to an enhancement of shear bond strength through chemical interaction between adhesives and substrates. Therefore, our work highlights an efficient method of laser surface treatment on the adhesion property of FDM-printed substrates.     

Effect of Silane Coupling Agent on the Mechanical Properties of Clay Filled Styrene Butadiene Rubber

Abstract

The effect of treatment of coupling agent [Bis (3-triethoxy-silyl-propyl) tetrasulphide] on mechanical properties of composites made from styrene butadiene rubber and clay is reported in this paper. The coupling agent in the form of solution (1.0%) was used for treatment of the filler. The treatment resulted in enhancement of mechanical properties of composites when compared with composites containing untreated clay. The properties under consideration were tensile strength, modulus at 100% and 400%, Young's modulus, hardness, etc. Good reinforcement was observed due to treatment of 1% coupling agent. Tensile strength was improved by 11%, modulus at 400% was found to improve by 237%, elongation at break was improved by 250%, while Young's modulus also was improved by 298% for treated clay composites, respectively, at 0.41 volume fraction when compared with untreated clay composites.     

Strength and Durability of Epoxy-Aluminum Joints

The adhesive strength and durability of adhesively-bonded aluminum joints in wet environments was analyzed. A2024-T4 alloy was subjected to two different surface treatments based on etching with chromic-sulfuric acid (FPL) and with sulfuric acid-ferric sulfate (P2). Small differences were observed in the lap shear strength as a function of the applied surface treatment. However, durability in humid environments was higher for the joints whose adherends were treated with P2.

Although the amount of water absorbed by the epoxy adhesive is lower in saline environments, the effects on the glass transition temperature of the epoxy adhesive and on the lap shear strength of the joints are more marked than the effects caused by aging with distilled water.

Finally, a new epoxy adhesive with a siloxanic hardener was tested, obtaining good mechanical properties, high glass transition temperature, moderate values of lap shear strength, and high durability in wet environments.     

A bio-based adhesive composed of polyelectrolyte complexes of lignosulfonate and cationic polyelectrolytes

Abstract

Polyelectrolyte complexes composed of lignosulfonate and cationic polyelectrolytes were used as bio-based adhesives. Sodium lignosulfonate (L-SO₃Na), a wood-derived anionic polyelectrolyte, was combined with three different cationic polyelectrolytes and the adhesive strength of the resulting complexes was evaluated on various substrates. Higher adhesive strength was observed with polar substrates (stainless steel, aluminum, and wood) compared to a nonpolar substrate (polypropylene). Complexes L-SO₃Na/poly(allylamine) and L-SO₃Na/ε-poly-l-lysine exhibited higher adhesive strength than the other polyelectrolyte complexes on aluminum and a commercial polyvinyl acetate adhesive on wood. In addition, our adhesives do not require any additional chemical reagents, such as organic solvents, crosslinkers, or condensation agents. The L-SO₃Na/ε-poly-l-lysine complex is a strong and completely biodegradable adhesive. This study demonstrates the use of lignosulfonate in the development of low-toxicity, sustainable, and biodegradable adhesives with excellent adhesive strength.     

The shear strength of composite secondary bonded single-lap joints with different fabrication methods

Abstract

The shear strength of composite secondary bonded single-lap joints was studied in this article. To optimize the adhesive thickness and ensure stable mechanical properties, an improved mold was applied. Based on this mold, a total of 15 specimens (180 samples) were examined and they were fabricated with various overlap lengths, curing pressures, adhesive thicknesses, ply angles, and surface treatment methods. The experimental results indicated that the improved mold not only significantly increased the uniformity of the adhesive thickness but also enhanced the shear strength of the joints and the shear strength was improved by approximately 13% compared to that of conventional methods. Moreover, the shear strength was decreased in specimens with increased overlap lengths and increased in samples with an increased curing pressure. Furthermore, the shear strength of the specimens was also affected by the adhesive thicknesses, ply angles, and surface treatment methods. The mechanisms can be ascribed to the effect of the fabrication method on the failure mode. A facile platform for optimizing these parameters is provided in this article. Based on this platform, the shear strength of the joints was enhanced to 33.5?MPa.     

Effects of different surface treatments of zirconia on the bond strength of self-adhesive resinous cement

Purpose: The aim of this study was to evaluate the effects of different zirconia surface treatments on the bond strength of two self-adhesive resinous cements (SARC).

Methods: Two hundred and eight cylindrical specimens were obtained from Y-TZP zirconia (half with diameter 3.2 mm and half with 4.8 mm). After sintering and polishing, specimens were divided into four groups (n = 26), according to surface treatment: Control (no treatment); Sandblasting (Al₂O₃ particles); Rocatec (Al₂O₃ particles, tribochemical silica coating and silane application); Laser (Nd: YAG laser: 20 Hz, 100 mJ, 0.2 J/cm²). The surface roughness (Ra) was evaluated after the surface treatments, and the groups were divided into two subgroups (n = 13), according to the SARC tested: RelyX U200 and Bifix SE. The 2.2-mm cylinders were bonded to 4.8-mm cylinders and stressed until failure under shear using a universal testing machine. Bond strength and Ra were analyzed using ANOVA, and Tukey’s test (α = 0.05).

Results: Surface treatment was significant (p < 0.0001), but cement type (p = 0.73) was not. Related to roughness, significant differences were found for the treatment type (p < 0.0001), with laser being the treatment with higher Ra values.

Conclusions: Nd:YAG laser produced a rougher surface and a higher bond strength compared with sandblasting, silicatization, and control groups.