Cr 6+ -free hybrid coatings as potential pretreatment for structural adhesive bonding

Transcription

1 Cr 6+ -free hybrid coatings as potential pretreatment for structural adhesive bonding Ph. Bringmann,. Rohr, J. Wehr I. Jansen Fraunhofer IWS

2 utline 1. Adhesive Bonding in Aircraft Industry 2. Surface Treatment with Si-organic Compounds 2.1 Silane/Sol-Gel based Coatings 2.2 Atmospheric Plasma deposited Coatings 3. Test Results 4. Summary 2

3 Structural adhesive bonding in aircraft industry Rudder Vertical Tail Plane (Skins, Ribs and Spars) Spoiler GLARE Elevators Flaps Slats Radome Horizontal Tail Plane (Skins, Ribs and Spars) Stringers Doublers Nacelles Fan-Cowls Rear Pressure Bulkhead Section 19.1 Section 19 Front, Body and Wing Landing Gear Doors Ailerons 3

4 Structural adhesive bonding in aircraft industry Stiffening of shells stringer A380 HTP-Skin doubler Inner flap A380 Wing rib (A380) T-Stringer VTP-Skin (A330) 4

5 Structural metal bonding - concepts Pre-treatment for structural metal bonding NH2 NH2 N Cr 6+ based pickling Status quo ADHESIVE Solvent cleaning and degreasing Alkaline degreasing Cross section Alkaline etching (removal of MDL) Cr 6+ free pickling (H 2 S 4 /Cr 3 ) Si Si R Si Si Si Si R R Si R Chromic acid anodising Si Si Cr 6+ free anodising R Al Si Si Tr R Si Si Si Si - R Rprocesses, Cr 6+ R Si - Silicon Al - Aluminium e.g. PAA, PSA, Tr loaded Si bonding Tr primer Tr Tr Al Al AC-Anodising Laser XIDE LAYER METAL ALLY Cr 6+ free surface treatment Penetration Cr 6+ free Tbonding of - primer Transition primer metal Si R - rgan. Gruppe Into oxide film R (chemically Face-to-face etched -rgan. Spacer -Sauerstoff xygenoff) Cr 6+ - replacement ADHESIVE BNDING PRIMER CUPLING LAYER XIDE LAYER METAL ALLY Cr 6+ free pickling Adhesion Coupling promoting layers: silanes coatings & incl. other coupling corrosion barrier agents thick, sol-gel dense layers sol-gel (thin) layer Primer thickness 3 µm atmospheric plasma Combined Cr 6+ -replacement deposition long-term concept 5

6 Structural adhesive bonding in aircraft industry Testing and requirements (among others) Pull-off test: preliminary test (screening) dry and after hot/wet exposure cohesive failure values like anodising Floating roller peel test (EN ) dry & wet cohesive failure peel strength > 10 kn/m (FM73 M.06) Bondline corrosion test exposure of bonded AA2024 clad to neutral salt fog Crack acidic zone Polymer Crack Polymer xide AA 1100 Anode AA 2024 Cathode 6

7 utline 1. Adhesive Bonding in Aircraft Industry 2. Surface Treatment with Si-organic Compounds 2.1 Silane/Sol-Gel based Coatings 2.2 Atmospheric Plasma deposited Coatings 3. Test Results 4. Summary 7

8 Surface treatment with Si-organic compounds Silane/sol-gel based coatings covalent bonding to metal oxide and polymer tested systems: (AA2024, alkaline etching, acidic pickling) γ-glycidoxipropyltrimethoxysilane (GPS) Australian Surface Treatment 1 wt.% in H 2, 1h hydrolysis, dip coating, 100 C curing AC-130 (Boeing, Boegel EPII) commercialized, aqueous sol-gel based on GPS and Zr-n-propoxide, > 30 min hydrolysis, spray drenching, RT curing, appr. 200 nm EADS silane mixture, Z-n-p, max. 90 min hydrolysis, dip coating, 120 C curing EC slightly modified AC-130, 60 min hydrolysis, dip coating, 120 C curing D. Raps, Diss

9 Surface treatment with Si-organic compounds Atmospheric pressure plasma deposition dry, out-of-bath, no curing surface treatment Plasmatreat plasma jet activation of substrate surface Single jet source Controled arc Process gas: air FMT plasma jet (Univ. Wuppertal) Multi jet source Barrier discharge Process gas: He Precursors: HMDS & TES Bubbler feed m feed /m film = 0,25 % m feed /m film = 0,013 % 9

10 Atmospheric pressure plasma deposition Thickness and composition measurement by XPS depth profiling Plasmatreat: FMT: film Concentration [at%] Si C HMDS TES film Concentration [at%] Si C HMDS TES Film thicknesses: < 200 nm 10

11 utline 1. Adhesive Bonding in Aircraft Industry 2. Surface Treatment with Si-organic Compounds 2.1 Silane/Sol-Gel based Coatings 2.2 Atmospheric Plasma deposited Coatings 3. Test Results 4. Summary 11

12 Adhesion (2-component epoxy) Pull-off test of sol-gel systems (ref.: PSA): pull-off strength [MPa] AA2024 bare (1.0 mm) dry 10 d 70 C 95%rh AA2024 clad (1.2 mm) pull-off strength [Mpa] dry 10 d 70 C 95%rh 0 EADS EADS (Ethanol) AC-130 PSA mostly cohesive failure 100 % mostly adh. failure mixed 100 % comparable results to coh. anodising on AA2024 bare failure (etched) coh. 0 EADS EADS (Ethanol) AC-130 significantly lower adhesion on AA2024 clad (etched) PSA 12

13 Adhesion (2-component epoxy) avg. peel strength [kn/m] Floating roller peel test of silane/sol-gel systems (ref.: CAA): AA2024 bare CAA etched GPS AC-130 EADS dry wet dry peel strength in the range of CAA for GPS & AC-130 severe deterioration after water injection for etched & AC-130 mostly cohesive failure within sol-gel film for EADS system peel strength only 50 % of CAA (dry & wet) adhesive sol-gel 2024 bare 13

14 Adhesion (1-component film-epoxy) Floating roller peel test of silane/sol-gel systems: AA2024 bare (etched) avg. peel strength [kn/m] roller peel FM73 GPS AC-130 EC (< 200 nm) EC (1 µm) D. Raps, Diss dry wet severe deterioration after water injection for GPS & AC-130 EC shows promising results even after water injection (stabilisation by thermal curing?) thickening of sol-gel film decreases peel strength of bond drastically TF-SIMS intensities vs. curing condition 14

15 Adhesion (2-component epoxy) Floating roller peel test of atmos. plasma coatings: Fracture transition dry wet (peel sheet) Plasmatreat TES avg. peel strength [kn/m] avg. peel strength [kn/m] PLASMATREAT plasma act. FMT HMDS 1 SLM HMDS 0.5 SLM TES 5 SLM TES 0.5 SLM dry wet dry wet FMT TES 0 HMDS HMDS EURADH 2008/ADHESIN 5 x 5 SLM 08 1 x 5 SLM TES 5 x 5 SLM TES 1 x 5 SLM 15

16 AA2024 clad samples after 30 d of NSST: Bondline corrosion Plasmatreat TES Plasmatreat activated GPS AC-130 EADS severe corrosion and delamination already after 30 d!!! no protection by sol-gel EC (< 200 and nm) plasma deposited coating no protection due to higher thickness or higher curing T EC (1 µm) 16

17 Adhesion (1-component film-epoxy) Drastically weak performance of literature known systems on etched substrate Application of GPS and AC-130 on alumina grit-blasted surfaces Floating roller peel test of GPS & AC-130: avg. peel strength [kn/m] Bondline corrosion still under investigation! gritblasted AC-130 dry peel strength gritblasted GPS No significant change upon water contact! unclad clad 17

18 utline 1. Adhesive Bonding in Aircraft Industry 2. Surface Treatment with Si-organic Compounds 2.1 Silane/Sol-Gel based Coatings 2.2 Atmospheric Plasma deposited Coatings 3. Test Results 4. Summary 18

19 Summary Si-organic based coatings for structural adhesive bonding tested deposition by wet-chemical sol-gel or by atmospheric plasma jet promising adhesion results on AA2024 bare (etched) significant lower adhesion of sol-gel coatings on AA2024 clad (etched) high peel strength on bare and clad substrate by GPS- & AC-130 treatment after grit-blasting no protection against bondline corrosion achieved! (etched Al) no enhancing of bondline protection due to higher thickness or higher curing temperature 19

20 Acknowledgements Thanks to I. Jansen Fraunhofer IWS. Rohr EADS IW J. Wehr EADS IW F. J. Gammel EADS IW D. Raps EADS IW M. Kolb EADS IW FMT Wuppertal Parts of this work were supported by the NANBASE (Förderkennzeichen: 03X0023B) project and to 20

21 What should be bonded? Materials in modern civil aircrafts Percentage of materials (Structure without engines) Al 70% Al 68% Al 20% Composite 52% CFRP 11% Steel 11% Ti 7% CFRP 17 % Steel 9% Ti 4% other 7% Ti 14% Steel 7% Boeing 777 Airbus A 340 Airbus A 350 TDAY TMRRW 21

22 Structural adhesive bonding in aircraft industry GLARE > 5 bar Autoclave free bonding (BIF) stringer Carbon Prepreg ply (t = 0.125; 0.25mm) doubler Inner flap A380 Titanium sheet (t = mm) Fuselage: stringers and doublers 22

23 Structural adhesive bonding in aircraft industry Requirements & goals for novel pre-treatments: Service-life > 30 a in harsh environments outstanding durability Cohesive failure of bonded joints even under peel loads Fulfill environmental, health and safety regulations Compatibility with new developments in manufacturing (large integral structures) Suitability for repair Suitability for different substrates Reduction of time and effort 23

24 Neutral salt spray test Sol-gel coated AA2024 bare after exposure to salt fog: CAA 168 h EADS > 200 h AC h 24

25 Jetquelle Uni Wuppertal tube in tube System Trennung von Plasma- und Reaktivgas sichtbare Jetlänge bis 50 mm Elektroden He Precursor Prinzipieller Aufbau einer Singlejet- Quelle ~ Multijetquelle aus 10 Singlejetquellen 25

26 Ti6Al4V pull-off results dry 30 d 70 C 95%rh 26 pull-off strength [MPa] CAA plasma activated TES (0,5 SLM) AC-130 gritblasted AC-130