overview of coatings in the automotive industry

Overview of Coatings in the

Automotive Industry

Erik Galdames

Bach. Of Eng.

E-46800 Xativa (Spain)

Content

• Main groups of coating systems

• Electroplating finishes

• Zinc flake coatings

• Conversion coatings

• Mechanical plating

• E-coating

• Main applications for fasteners

Main groups of coating systems

Coating system Coating

technique

Material Used on Post

treatments

Corrosion

protection

Colour

Electroplating Electrolytic Metallic Metallic parts Yes Cathodic/Barrier Various, mainly

silver

Zinc flake coatings Dip-

spinning,

spray

Contains metals Metallic parts Yes Cathodic Silver

Organic coatings Dip-

spinning,

spray

Organic Metallic parts Yes Barrier Various

Top-coats Dip-

spinning

Organic/Inorgan

ic

Applied over

base coat

Possible Barrier Transparent/Black

E-coat

Electrophor

etic

Organic

Applied over

base coat

No Barrier Black

Conversion

coatings

Chemical

reaction

Metallic

parts/Applied

over metallic

coatings

Yes Temporary Silver

Yellow

Black

Lubricants Dip-

spinning,

static

Organic Metallic

parts/Applied

over metallic

coatings

No Temporary Transparent/Dark

Mechanical plating Mechanical Metallic Metallic parts Yes Cathodic Silver

Micro-encapsulated

Locking feature

Spraying

Organic Coated parts No Barrier Various

Main groups of coating systems

Coating system Description

Electroplating Electrolytic metallic coatings, pure or alloyed. Used in combination of passivation and top-coats and lubricant.

Good adhesion, uniform coating distribution, good temperature resistance. Non resistant to acids/alkaline products

except Ni, Cu, Cr, resistance to organic solvents. Susceptible to hydrogen embrittlement. ZnNi less susceptible to

hydrogen embrittlement. Good electrical conductivity. Reliable coating technology

Zinc flake coatings Coatings contain Zn and Al flakes in an anorganic matrix. Dip-spin or spray. Used in combination with top-coats

and lubricants. Medium adhesion, fair ductitlity, sensitive to wear. Non resistant to acids/alkaline products, resistant

to organic solvents. Fair electrical conductivity. Modern coating technology

Organic coatings Organic paints. Better to be used in combination of zinc flake coatings or phosphated surfaces. No cathodic

protection. Fair adhesion, good ductility, sensitive to wear. Good resistance to acids/alkaline products, good

resistant to organic solvents. Non-electrically conductive. Available in various colours. Modern coating technology

Top-coats Organic and inorganic layers of nanoparticles. They offer sealing effect and increase corrosion protection of zinc

flake coatings and electroplated surfaces. With and without solid integrated lubricant. Non resistant to

acids/alkaline products. Fair electrical conductivity. Modern coating technology

E-coat

Organic coatings applied by electrophoretic technology. Used in combination of Zn or ZnNi electroplating. Excellent

black finish. Non-electrically conductive. Modern coating technology

Conversion

coatings

Applied by chemical reaction to a metallic substrate (phosphating) or metallic coating (Cr6-free passivation). No

increase in coating thickness. Temporary corrosion protection. Good friction properties. Reliable coating technlogy

Lubricants They produce a regulation of coefficient of friction to reduce friction. Some provide temporary corrosion protection.

Reliable technology

Mechanical plating Metallic coatings, pure or alloy applied by friction (mechanical interaction). Used in combination of passivation and

top-coats and lubricant. Good adhesion, uniform coating distribution, good temperature resistance. Non resistant to

acids/alkaline products, resistant to organic solvents. Non-susceptible to hydrogen embrittlement. Very good

electrical conductivity. Old fashioned coating technology. Reduced availability of suppliers.

Micro-encapsulated

Locking feature

Partial coatings with self-locking properties for threaded fasteners. Adhesive coatings and self-locking coatings.

Organic materials

Electroplating finishes

Coating

system

Layer

thickness

Cathodic

protection

WR/RR Conversion

coating

capability

Top-coat Weldabil

ity

Conductivity Service temp.

Zn 8 µm YES 48/96 h YES YES Good YES 90ºC

ZnFe 8 µm YES 120/380 h YES YES Medium YES 120ºC

ZnNi 8 µm YES 120/720 h YES YES Medium YES 150ºC, 300ºC**

ZnSn 8 µm YES 120/720 h YES NO Very

good

YES 120ºC

Cu 3 µm NO N.A. NO NO Good YES 250ºC

Ni

10 to 20 µm NO N.A. NO NO -- YES 250ºC

Sn 5 to 15 µ NO N.A. Mainly not NO Very

good

YES 90ºC

CuNiCr 10/25/0,3

µm

NO 480 NO NO -- YES 150ºC

Ag 5 µm NO N.A. NO NO -- YES 150ºC

* Service temperature is the maximum temperature at which coatings maintain their main properties.

Though their melting temperature is higher, some characteristics like corrosion resistance will be

reduced

** Temporary local temperatures. E.g. normal service temperature 150ºC, short exposition to peaks of

300ºC can be reached

Zinc flake coatings

Coating

system

Layer

thickness

Cathodic

protection

WR/RR Curing

temp.

Top-coat Weldabil

ity


Geomet 6 µm YES 200/600

200/1000

300ºC YES Poor Poor 300ºC

Delta

Protekt

9 µm YES 240/840 240ºC YES Poor Poor 240ºC

Magni 10 µm YES 240/840 240ºC YES Poor Poor 240ºC

Zintek 10 µm YES 200/720 240ºC YES Poor Poor 240ºC

Conversion coatings

Coating

system

Layer

thickness

Cathodic

protection

WR Substrate Top-coat Colour Application Service

temp.

Cr

passivation

0,1 to 0,3

µm

NO Zn 48 h

ZnFe 96 h

ZnNi 120

h

Zn

ZnFe

ZnNi

Yes Transp.

Yellow

Black

Improves corrosion

protection (WR)

90ºC

ZnPh

MnPh

3 µm NO 6 h

(oiled) 24

h

Fe Yes

Oil

Dark grey Temporary corrosion

protection

Base for paints

Lubrication properties

90ºC

Mechanical plating

Coating

system

Layer

thickness

Cathodic

protection

WR/RR Conversion

coating

Top-coat Weldabil

ity


Zn 5 µm YES 48/96 h YES NO Very

good

Very good 90ºC

Sn 3 µm YES 48/96 h YES NO Very

good

Very good 90ºC

E-coating

Coating

system

Layer

thickness

Cathodic

protection

WR/RR Colour Top-coat Substrat

e


KTL 5 µm NO -/120 h Black YES Fe Non-

conductive

200ºC

Zn+KTL 8 µm (only

KTL)

NO (only

the base

coat

provides it)

CC Test Black YES Zn Non-

conductive

90ºC

ZnNi+KTL 8 µm (only

KTL)

NO (only

the base

coat

provides it)

CC Test Black YES ZnNi Non-

conductive

90ºC

Main applications for fasteners

Coating Typical applications Adequate for Less adequate for

Zinc flake coatings Chassis

Motor compartment (areas

exposed to high corrosivity)

Aluminium joints

Bolts ≥ 10.9

Microencapsulated coating

allowed (without lubricated top-

coat)

Ground connections

External thread <M6

Internal thread <M10

Internal drive features T30

ZnNi Chassis



Aluminium joints

External thread < M6

Internal thread < M10

Bolts ≥ 10.9, ≥ 1000 N/mm2

Though less hydrogen

embrittlement risk than pure e-

plated Zn.

Service temperature > 150ºC

ZnNi black Chassis



Aluminium joints

External thread < M6 with

internal drive feature

Internal thread <M10

Self-tapping screws

Bolts ≥ 10.9, ≥ 1000 N/mm2

Though less hydrogen

embrittlement risk than pure e-

plated Zn.


Phosphating + oil Multicomponent, oil circuits or

transportation

Parts in motion without

corrosion exposure

Transport and limited storage

in warehouses

Parts not multi-component


Zn+passivation+top-coat

(silicate)

Mg alloys Parts in contact with

magnesium alloys

Bolts ≥ 10.9

Zn+passivation Weld parts Weld parts Bolts ≥ 10.9

overview of coatings in the automotive industry

Technology