金属表面涂装工艺
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10
Anodizing
• Al & Mg alloys can be anodized (Mg not discussed)
• Two types for Al
– Standard anodizing: Forms thin oxide layer that can be dyed – Hard anodizing: Forms thick oxide layer for wear resistance
COATING
1
Coating
A relatively thin layer of material, usually 1 mm or less in thickness, applied by various processes for the purpose of corrosion prevention, oxidation, wear, lubrication, cosmetics, identification, or some combination of these or other purposes.
• Process
– Electochemical process using sulfuric acid bath – Al part is the anode – When voltage applied water breaks down on surface and Al
reacts with oxygen to form an aluminum oxide layer – Aluminum oxide (Al2O3) layer protects Al metal – Aluminum oxide is a hard ceramic (good wear properties)
2H+ + 2e- H2
– Anode (Oxidation, Zinc goes into solution)
Zn0 Zn+2 + 2e-
– Side Reaction (oxygen produced from water)
H2O
1 2
O2
+ 2e-
13
Metallic Coatings: Electrolytic
and other requirements, e.g., hydrogen embrittlement bake
15
Metallic Coatings: Electrolytic
• Tin Plating
– Common for terminals and parts that are to be soldered – Used where part electrical grounding is needed – Typical specification used ASTM B545 – Print callout example:
– Used as pretreatment for:
• Substrate coating to improve paint adhesion • Corrosion protection • Cold forming (improves lube carrying) • Improving sliding frictional properties of surface (Mn Phosphate)
2
Coating Technologies
• Inorganic
– Conversion Coatings
➢ Phosphates ➢ Chromate (Cr+6) and Chromite (Cr+3) ➢ Black Oxide (Fe alloys only, Fe3O4 film [magnetite])
protective layer • Increased corrosion resistance obtained by using silicate
based sealers over conversion coating layer
8
Inorganic: Conversion Coatings
Zn2+ 百度文库n2+
Anode
12
Metallic Coatings: Electrolytic
• Reactions
– Cathode (Reduction, Zinc is deposited on part)
Zn+2 + 2e- Zn0
– Side reaction (Hydrogen produced Hydrogen Embrittlement)
• Black Oxide – Black finish
• Thin iron oxide layer formed • Fe3O4 magnetite
– Ferrous parts only – Processing
• Immersion temperature: 285-295 deg. F • Proprietary solution of:
5
Inorganic: Conversion Coatings
• Phosphate Coatings
– Surface of iron or zinc reacts and coating is deposited
– Types
• Zinc Phosphate • Iron Phosphate • Manganese Phosphate
Hot-Dip (Zinc, Tin) (Will not discuss)
Physical Vapor Deposition (PVD) (Will not discuss)
➢ Aluminum ➢ Chromium
4
Coating Technologies
• Organic
– Coating Types
16
Matte Tin Plate, 5 microns, Ni underplate per ASTM B545
– Finish:
• Matte (dull appearance) • Bright (shiny)
– Underplate
• Copper or Nickel used • Required for brasses with 5% or greater Zn content • Acts as diffusion barrier to zinc
14
Metallic Coatings: Electrolytic
• Platings used
– Zinc (DX551200)
• Most common type of plating used • Requires use of approved source • Proper print callout example
Zinc plate DX551248 6K144/96W per DX551200
➢ DX551248 is the subspec in DX551200
➢ 6 means 6 microns Zn plate thickness minimum ➢ K denotes clear coating appearance ➢ 144 means minimum hours to red rust in Neutral Salt Spray (NSS) ➢ 96 means minimum hours to white rust in NSS ➢ W denotes a type of post treatment, in this case sealer + wax ➢ Including per DX551200 important because this specifies the tests methods
• Hard Anodize used for Al AC compressor pistons
11
Metallic Coatings: Electrolytic
• Electrolytic Cell
V
e-
e-
Zn0 Zn0
Cathode
Zn2+
Zn2+ Plating Solution
Zinc Plated Layer
➢ Zinc, Nickel, Chrome, Copper, Tin, Silver, Gold, etc. ➢ Alloys: Zn-Fe, Zn-Ni, Zn-Co, Zn-Sn, Brass, etc.
Electroless
➢ Copper ➢ Nickel
Mechanical (Zinc)
• Baking causes H atoms in steel to “spread out more” • Baking guidelines must be strictly followed:
– Maximum time allowed after plating for baking to start – Bake temperature – Time at temperature
– Sodium hydroxide – Sodium nitrate – Sodium nitrite – Other chemicals
• Time: 5-20 minutes depending on alloy and surface
9
Typical Black Oxide Appearance
• Solvent Base (Polymer dissolved in solvent) • Aqueous Base (Water based paint emulsion) • Powder
– Application Methods
➢ Spray ➢ Dip ➢ Dip-Spin ➢ Electrocoat ➢ Autodeposition (will not cover) ➢ Fluidized bed (powder)
IMPORTANT!!! CHROMATES ARE BANNED
➢ EU ELV & WEEE Directives (Asia following)
– Trivalent Chrome Type
• Used on Zinc and Zinc-Alloy Electroplated Coatings • Reaction with dissolved zinc produces zinc chromium oxide
6
Structure of Zinc
Phosphate Coatings
7
Inorganic: Conversion Coatings • Chromium Based Conversion Coatings
– Two Types
• Chromate (Cr+6, hexavalent chrome) • Chromite (Cr+3, trivalent chrome) (Note: You will hear & see people use trivalent chromate)
• Hydrogen Embrittlement
– Problem: Elemental hydrogen (H) diffuses into steel surface – H atoms later combine causing delayed catastrophic failure
Example: Screw heads start breaking off on assemblies – Steels > Rockwell C 32 (some say 36) susceptible – Fix: Plated steel parts MUST be baked after plating
Anodized (Aluminum) Chemical Vapor Deposition (CVD) (Will not discuss)
➢ Diamond-like ➢ Titanium Nitride (TiN)
3
• Metallic
Coating Technologies
– Electrolytic
Anodizing
• Al & Mg alloys can be anodized (Mg not discussed)
• Two types for Al
– Standard anodizing: Forms thin oxide layer that can be dyed – Hard anodizing: Forms thick oxide layer for wear resistance
COATING
1
Coating
A relatively thin layer of material, usually 1 mm or less in thickness, applied by various processes for the purpose of corrosion prevention, oxidation, wear, lubrication, cosmetics, identification, or some combination of these or other purposes.
• Process
– Electochemical process using sulfuric acid bath – Al part is the anode – When voltage applied water breaks down on surface and Al
reacts with oxygen to form an aluminum oxide layer – Aluminum oxide (Al2O3) layer protects Al metal – Aluminum oxide is a hard ceramic (good wear properties)
2H+ + 2e- H2
– Anode (Oxidation, Zinc goes into solution)
Zn0 Zn+2 + 2e-
– Side Reaction (oxygen produced from water)
H2O
1 2
O2
+ 2e-
13
Metallic Coatings: Electrolytic
and other requirements, e.g., hydrogen embrittlement bake
15
Metallic Coatings: Electrolytic
• Tin Plating
– Common for terminals and parts that are to be soldered – Used where part electrical grounding is needed – Typical specification used ASTM B545 – Print callout example:
– Used as pretreatment for:
• Substrate coating to improve paint adhesion • Corrosion protection • Cold forming (improves lube carrying) • Improving sliding frictional properties of surface (Mn Phosphate)
2
Coating Technologies
• Inorganic
– Conversion Coatings
➢ Phosphates ➢ Chromate (Cr+6) and Chromite (Cr+3) ➢ Black Oxide (Fe alloys only, Fe3O4 film [magnetite])
protective layer • Increased corrosion resistance obtained by using silicate
based sealers over conversion coating layer
8
Inorganic: Conversion Coatings
Zn2+ 百度文库n2+
Anode
12
Metallic Coatings: Electrolytic
• Reactions
– Cathode (Reduction, Zinc is deposited on part)
Zn+2 + 2e- Zn0
– Side reaction (Hydrogen produced Hydrogen Embrittlement)
• Black Oxide – Black finish
• Thin iron oxide layer formed • Fe3O4 magnetite
– Ferrous parts only – Processing
• Immersion temperature: 285-295 deg. F • Proprietary solution of:
5
Inorganic: Conversion Coatings
• Phosphate Coatings
– Surface of iron or zinc reacts and coating is deposited
– Types
• Zinc Phosphate • Iron Phosphate • Manganese Phosphate
Hot-Dip (Zinc, Tin) (Will not discuss)
Physical Vapor Deposition (PVD) (Will not discuss)
➢ Aluminum ➢ Chromium
4
Coating Technologies
• Organic
– Coating Types
16
Matte Tin Plate, 5 microns, Ni underplate per ASTM B545
– Finish:
• Matte (dull appearance) • Bright (shiny)
– Underplate
• Copper or Nickel used • Required for brasses with 5% or greater Zn content • Acts as diffusion barrier to zinc
14
Metallic Coatings: Electrolytic
• Platings used
– Zinc (DX551200)
• Most common type of plating used • Requires use of approved source • Proper print callout example
Zinc plate DX551248 6K144/96W per DX551200
➢ DX551248 is the subspec in DX551200
➢ 6 means 6 microns Zn plate thickness minimum ➢ K denotes clear coating appearance ➢ 144 means minimum hours to red rust in Neutral Salt Spray (NSS) ➢ 96 means minimum hours to white rust in NSS ➢ W denotes a type of post treatment, in this case sealer + wax ➢ Including per DX551200 important because this specifies the tests methods
• Hard Anodize used for Al AC compressor pistons
11
Metallic Coatings: Electrolytic
• Electrolytic Cell
V
e-
e-
Zn0 Zn0
Cathode
Zn2+
Zn2+ Plating Solution
Zinc Plated Layer
➢ Zinc, Nickel, Chrome, Copper, Tin, Silver, Gold, etc. ➢ Alloys: Zn-Fe, Zn-Ni, Zn-Co, Zn-Sn, Brass, etc.
Electroless
➢ Copper ➢ Nickel
Mechanical (Zinc)
• Baking causes H atoms in steel to “spread out more” • Baking guidelines must be strictly followed:
– Maximum time allowed after plating for baking to start – Bake temperature – Time at temperature
– Sodium hydroxide – Sodium nitrate – Sodium nitrite – Other chemicals
• Time: 5-20 minutes depending on alloy and surface
9
Typical Black Oxide Appearance
• Solvent Base (Polymer dissolved in solvent) • Aqueous Base (Water based paint emulsion) • Powder
– Application Methods
➢ Spray ➢ Dip ➢ Dip-Spin ➢ Electrocoat ➢ Autodeposition (will not cover) ➢ Fluidized bed (powder)
IMPORTANT!!! CHROMATES ARE BANNED
➢ EU ELV & WEEE Directives (Asia following)
– Trivalent Chrome Type
• Used on Zinc and Zinc-Alloy Electroplated Coatings • Reaction with dissolved zinc produces zinc chromium oxide
6
Structure of Zinc
Phosphate Coatings
7
Inorganic: Conversion Coatings • Chromium Based Conversion Coatings
– Two Types
• Chromate (Cr+6, hexavalent chrome) • Chromite (Cr+3, trivalent chrome) (Note: You will hear & see people use trivalent chromate)
• Hydrogen Embrittlement
– Problem: Elemental hydrogen (H) diffuses into steel surface – H atoms later combine causing delayed catastrophic failure
Example: Screw heads start breaking off on assemblies – Steels > Rockwell C 32 (some say 36) susceptible – Fix: Plated steel parts MUST be baked after plating
Anodized (Aluminum) Chemical Vapor Deposition (CVD) (Will not discuss)
➢ Diamond-like ➢ Titanium Nitride (TiN)
3
• Metallic
Coating Technologies
– Electrolytic