Transcript The Combined AC/DC Anodising of Automotive Grade 6060.35

Pretreatments for the Optimised
Adhesion of Aluminium in Aerospace
Applications
G.W.Critchlow
Department of Materials, Loughborough University, UK
Greece, Daedalus and Icarus – 1300 to 1000
BC
Metal technology Development
Technology
introduction
A318
• EB and extended LBW
A380 • Al-Li alloys, Ti-alloys
• Al-alloys: 2024HDT, 7055HF
• Large die forging (7085)
• New coatings
• Larger panels
• New assembly concepts
• Laser beam welding LBW
• 6013/6056 Al-alloys
• New bonding technology
A340-600/-500
A330/340
A320
A300/A310
• SPF Ti
• Chemical milling
• 7475 Al-alloy sheet/plate
• Interference bolting
• Premium Al-castings
• 7349 Al-alloy extrusions
• Split mandrel cold working
• Age forming
• High Speed Machining
• 2X24 Al-alloys
• LVER* riveting
• SPF Al
• High strength Al-castings
• 7150 Al-alloy plate (wing)
• Automated Lok bolting
• Split sleeve cold working
Durability or permanance of the bonded
structure is a function of:
Alloy
 Al 7075-T6 clad/bare
 Al 2024-T3 clad/bare
 Adhesive
 FM 73 Film Adhesive
 Coupling agent/primer
 BR 127 Primer
 Surface condition
Siegbahn
Manne Siegbahn 1924
Kai Siegbahn -1981
God made materials but surfaces are the Devil’s work
Kai Sieghbahn
Ideally, surface should be:
 free from contamination
 wettable
 rough
 mechanically stable
 hydrolytically stable
Pretreatment options
 Mechanical (degrease, grit-blast, laser texturing,
cryoblasting)
 Chemical (acid etch, conversion coating)
 Electrochemical (anodic oxidation)
Standard Processes – 40/50V CAA
Pore
diameter
25nm
Cell wall
thickness
10nm
Oxide
thickness
4 m
Barrier
layer
Base
Metal
CAA 40/50V Anodising Process
Isoprep 44
FPL Etch
CAA
Seal
60g/l
Concentration
(pH 9.3 –10.45)
60g/l – Na2Cr2O7
166ml/l – H2SO4
1.5g/l – Al
30.5 – 50.0g/l
DI Water
10 minute
Submersion
30 minute
Submersion
35 – 45 minute
Anodising
15 minute
Submersion
60°C
60°C
40°C
Min 96°C
MEK
Solvent
Wipe
Vapour
Degrease
Alkaline
Clean
RinseDI Water
Acid
Etch
RinseDI Water
Anodise
RinseDI Water
Optional
Seal
Optional
Rinse
Hot Air
Dry
J.L. Cotter and R. Kolhler,
Int.J.Adhesion & Adhesives, 1981
Disadvantages of CAA
 There are health & safety and environmental issues
associated with the use of hexavalent chromium.
 Process is highly complex and time consuming to
completion – costly.
3. Alternatives to CAA
Alternatives to Hexavalent Chromium
 Trivalent Chromate
• First and Second Generation Systems
 Non-Chromated Conversion Coating
• Sol-Gel (BAC 5663)
• Silane Coupling Agents
 Non-Chromated Anodising
• Phosphoric Acid Anodising, PAA (BAC5555)
• Boric Sulphuric Acid Anodising, BSAA (BAC 5632)
• Phosphoric Sulphuric Acid Anodising (Airbus, Germany)
 Friction stir welding – alternative to bonding
 Use of Composites – alternative to aluminium
3.5 ACDC process
AC offers:
 Degrease only required
 Open porous structure
 Rapid processing
DC offers:
 Thick, compact film
Anodic reactions




2Al +6OH- → Al2O3 + 3H2O + 3eAl → Al3+ + 3e4OH- → 2H2O + O2 + 4e2SO42- →S2O82- +2e-
Cathodic reactions




2H+ + 2e- →H2
SO42- + 8H+ + 6e- → S + 4H2O
Al2O3 + 6H+ + 6e- → 2Al + 3H2O
Al3+ + 3e- → Al
Objective
To produce an AC/DC film in a single electrolyte
at a constant temperature with approx 300
nm of outer porous oxide and >1 micrometre
of inner dense oxide.
Variable parameters
Parameter
Electrolyte
AC
DC
mixed sulphuric-phosphoric
Voltage (V)
50Hz, 10-20
<25
Time (s)
120-240
600
Temperature
(°C)
RT-50
RT-50
Surface after AC anodising
degreased-only
5s AC anodising
30s AC anodising
120s AC anodising
240s AC anodising
surface atom % for the main element after different anodising
periods
55
45
atom%
35
Al(o)
C
25
O
15
5
0
50
100
150
-5
anodising periods (s)
200
250
surface atom% for second element after differents anodising
periods
19.5
17.5
15.5
13.5
P
atom %
11.5
S
Cl
9.5
K
7.5
Mg(o)
5.5
3.5
1.5
-0.5
0
50
100
150
anodising periods (s)
200
250
Slow dissolution
AlPO4
Al2O3
AlOOH
Al(OH)3
Influence of DC voltage
Thickness / microns
Film thickness Vs Voltage (10m)
2
1.5
1
0.5
0
0
5
10
15
Voltage / V
20
25
30
10v AC, 120 s: 20v DC, 600s @35°C