Environmental durability of corrosion sensitive aluminum alloys: one more step toward a more reliable laboratory evaluation of in service performance

Transcription

1 Powering your H2FC innovation Environmental durability of corrosion sensitive aluminum alloys: one more step toward a more reliable laboratory evaluation of in service performance Dr. Danick Gallant Ph.D., NACE Coating Inspector Research Officer Technical Leader Corrosion Control and Performance Evaluation of Lightweight Materials and Assemblies NRC Aluminum Technology Center North American Automotive Metals Conference Dearborn, MI, USA September 2-3,

2 Cost of corrosion The study entitled Corrosion Costs and Preventive Strategies in the United States was conducted from 1999 to 2001 by CC Technologies Laboratories, Inc., with support from the FHWA and NACE. In the US, direct cost of metallic corrosion is 276 B$ on an annual basis (3.1% US GDP) Transportation sector : 29.7 B$ For the motor vehicles (23.4 B$): B$ Corrosion-related depreciation of vehicles 6.45 B$ Repairs/maintenance made necessary by corrosion 2.56 B$ Increased manufacturing costs from corrosion engineering and the use of corrosion-resistant materials 2

3 Some corrosion challenges with aluminum that can affect structural integrity Galvanic corrosion: coupling with steel is of concern, but also CFRPs Stress corrosion cracking (SCC): one of the concerns with high strength alloys, although this phenomenon is known for more than 50 years. Corrosion-assisted fatigue (CAF): aluminum has no fatigue endurance limit, and its pitting susceptibility (some alloys) make them susceptible to CAF Protective coatings and adhesive joints disbonding: surface treatment challenges 3

4 Presentation agenda NRC Aluminum Technology Center contributes to find solutions to «showstoppers» in the use of aluminum. Today s AMM presentation adresses some of them: Corrosion protection of high-strength aluminum alloys: How can corrosion protection of aluminum underbody be simulated in the lab? Galvanic corrosion: numerical simulation in support to design engineer (i.e. corrosion people who speak the design engineer language!) Environmental durability of adhesive joints: How can automotive OEMs (buses, heavy trucks, trains, subways, specialty vehicles, cars) become more confident in the use of 2K epoxy and MMA adhesives? This presentation will emphasize on methodologies developed at NRC Aluminum Technology Center. 4

5 Corrosion and durability activities An integrated 3-level approach Level 1 - Electrochemical characterization - Determination of sensitivity to pitting corrosion, electrodissolution rate, filiform corrosion, SCC, etc. - Alloys selection and development - Rapid electrochemical assessment of coatings - Non destructive inspection Level 2 - Exposure to artificial environments - Cyclic corrosion testing (ISO, ASTM, SAE) - OEMs procedures (GMW, FLTM, Volvo) - Samples health monitoring during laboratory environmental exposure - Exposure to outdoor environments with intermittent salt spray Level 3 - Exposure to in-service conditions - Exposure of specimens to road conditions - Periodic samples removal for condition evaluation Current state-of-the-art + Data acquisition rate - - Prediction accuracy of inservice behavior + Data acquisition rate Where we are going Prediction accuracy of in-service behavior + 5

6 Corrosion protection of high strength aluminum alloys Painted AA7075-T6 samples exposed on vehicles Accumulation of saline mud, with minimum exposure to impact and erosion conditions Impact & erosion areas 6

7 Laboratory vs. in-service correlation In-service performance evaluation 8 months on road, from Sept. 25, 2014 to May 28, 2015; Approx. 36,000 km. Laboratory-scale characterization Coating resistance to impact / chipping at 20 C and 30 C; Coating resistance to cathodic disbonding; Coating impermeability to saline water; Adhesion durability. 7

8 Summary: coating selection procedure Electrochemical techniques are used at each of the 3 evaluation steps. Criterion # Parameter Time required 0 Coating selection 1 Impact resistance NA Condition to meet Cost, curing time, surface preparation requirements, etc. Coatings selected 15 coatings pre-selected 24 h R p,20 C + R p, 30 C 5000 Ω 2, 4, 7, 10, 13, 14, 15 2 Impermeability 24 h At t = 0 & t = 24h, Low-f Z 10 8 Ω 3 Adhesion durability 24 h After 24 h REAP, 0% adhesive failure at the Al-coating interface 2, 4, 10, 13, 14, 15 10, 14, 15 Total 72 h 3 coatings meeting requirements Do those lab results rely with in-service performance? 8

9 Painted AA7075 samples exposed on vehicles Row 8 Row 2 After 7 months on road (3 most performant coatings according to lab results) Coating #10 Coating #14 Coating #15 Row 2 Row 8 9

10 Painted AA7075 samples exposed on vehicles Row 2 Coatings that do not meet criterion #1: impact resistance Coating #1 Coating #3 Coating #5 Coating #6 Coating #8 Coating #9 Coating #11 Coating #12 10

11 Painted AA7075 samples exposed on vehicles Row 2 Coating that does not meet criterion #2: impermeability Coating #7 11

12 Painted AA7075 samples exposed on vehicles Row 8 Row 2 Coatings that do not meet criterion #3: adhesion durability Coating #2 Coating #4 Coating #13 12

13 A 2 nd laboratory approach for in-service performance prediction 7 months under the vehicle 2-day NRC laboratory procedure Coating #1 13

14 A 2 nd laboratory approach for in-service performance prediction 7 months under the vehicle 2-day NRC laboratory procedure Coating #2 14

15 A 2 nd laboratory approach for in-service performance prediction 7 months under the vehicle 2-day NRC laboratory procedure Coating #7 15

16 A 2 nd laboratory approach for in-service performance prediction 7 months under the vehicle 2-day NRC laboratory procedure Coating #10 16

17 A 2 nd laboratory approach for in-service performance prediction 7 months under the vehicle 2-day NRC laboratory procedure Coating #14 17

18 Why is corrosion-fatigue resistance so crucial? As matter of fact, among the five possible failure mechanisms that can jeopardize material strength, i.e.: Cleavage or brittle fracture; Plastic flow or ductile fracture; Fatigue; Corrosion; Creep; there is only one, namely corrosion, that can generate more damage than fatigue. Often, the two events combine giving rise to what can be considered the most devastating and unpredictable challenge of them all: corrosion assisted fatigue. Fatigue and Corrosion in Metals, Wiley,

19 Development of a corrosion assisted fatigue (CAF) & stress corrosion cracking (SCC) testing cell Cell concept & design Fabrication & installation Fatigue & corrosionfatigue results 19

20 Development of a corrosion assisted fatigue (CAF) & stress corrosion cracking (SCC) testing cell Corrosion cell designed for corrosion assisted fatigue (CAF) and stress corrosion cracking (SCC) installed on a servohydraulic machine with a 25 kn capacity, and equiped with 2 actuators for torsion and tension modes; Cell made of Ti64 et SS316 alloys; Solution continuously flows through the cell, at a controlled temperature; The sample is electrically insulated from the cell, thus allowing in situ electrochemical measurements and control; The cell can be used to evaluate bare alloys, protected alloys, adhesive joints, welded joints, etc; This cell will first be used for the development and evaluation of protective solution for AA7075 high strength aluminum alloy, which is sensitive to SCC. 20

21 ECN applied to corrosion-fatigue samples Detection of crack initiation σ avg I = 66 na 0.5% NaCl 60 Hz R = 0.1 ( MPa) Sample fails σ avg I = 124 na Crack initiation 21

22 Numerical simulation of galvanic corrosion FEA models inputs are experimental data (polarization curves) obtained from a variety of materials; Geometry, thin electrolyte layer, electrolyte conductivity, resistive behaviors can all be controlled; Galvanic corrosion behavior can be modeled over time: current density, electrolyte potential, local substrates thinning (etc.) can be measured. Aluminum Zn Steel 22

23 Numerical simulation of galvanic corrosion Numerical simulation of galvanic corrosion facilitates: selection of materials and fasteners; positioning of fasteners; identification of locations where sealants (or other insulation means) must be applied, and effective corrosion distances; overall discussions with design engineers. Al fastener 1-mm thick electrolyte Aluminum Steel 23

24 Adhesive joints exposed to in-service environments Winter exposure Nov to May

25 Temperature survey from Nov to May 2014 Saguenay, QC, Canada 25 Color chart (T, C)

26 NDI-EIS of Al-epoxy joint after 15,000 km Saguenay, QC, Canada, between Nov and May 2014 Aluminum Interface Adhesive Overall, for the 2K epoxy adhesive evaluated in combination with 4 surface treatments, the main moisture intrusion route is the Al-adhesive interface. #1 #18 Mechanical resistance loss (%) CPE (%) Position of the assembly 26

27 Durability of Al-epoxy adhesive joint Winter exposure - Nov to May Influence of surface treatment Road exposure Road conditions Lab exposure Road exposure Road conditions Lab exposure Road distance (km) Epoxy adhesive, basic surface treatment Hours of exposure in lab Road distance (km) Epoxy adhesive, chemical-based surface treatment Hours of exposure in lab Mechanical resistance loss (%) Mechanical resistance loss (%) After 15,000 km After lab exposure After 15,000 km 100% cohesive failure: what is the degradation mechanism? After lab exposure 27

28 Durability of Al-MMA adhesive joint Winter exposure - Nov to May 2014 System 1 Adhesive 1 + Surface Treatment 1 System 2 Adhesive 2 + Surface Treatment 2 Road exposure Road conditions Lab exposure Road exposure Road conditions Lab exposure Road distance (km) 100% cohesive failures Hours of exposure in lab Road distance (km) 100% cohesive failures Hours of exposure in lab Mechanical resistance loss (%) Mechanical resistance loss (%) 28

29 LGTV - ALTec Projects ALTec consortium, which is part of the NRC program in automotive lightweighting, is a pre-competitive R&D initiative launched in January By joining the group, you have access to results of the following ongoing projects: 1. Al/Steel friction stir welding (FSW): strategies and reduction of forces and moving toward a robotic solution 2. Development of durable structural adhesive joints of minimally pretreated multimaterial structures 3. Design and production of large hollow extrusions with thin walls 4. Mitigation of galvanic corrosion of aluminum in dissimilar material assemblies 5. Vacuum-assisted high pressure die casting of hollow aluminum structural nodes 6. Warm and hot forming of various aluminum sheet alloys at high production rates 7. Weldability assessment of Al alloy AA7075 and the esthetic optimization of lap joints 8. Evaluation of the in-service stress corrosion cracking (SCC) performance of high strength aluminum alloys 9. Heating coatings for multifunctional intelligent molds 10. Tribological coatings for multifunctional intelligent molds 29

30 Powering your H2FC innovation Thank you Dr. Danick Gallant Ph.D., NACE Coating Inspector Level 2 No Research Officer Technical Leader Corrosion Control and Performance Evaluation of Lightweight Materials and Assemblies NRC Aluminum Technology Center Office: Danick.Gallant@cnrc-nrc.gc.ca 30