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News

Surface preparation for bonding metals

Master Bond : 04 March, 2014  (Technical Article)
Master Bond manufactures a wide range of adhesives for bonding metals to metals, as well as metals to other substrates. Surface preparation plays a key role to ensuring that good bond strength is achieved. The following techniques are typically used as practices for proper surface preparation:
Degreasing
 
Degreasing is carried out in order to remove any loosely held dirt or other contaminants from the surface. Surfaces can be degreased using volatile solvents such as toluene, acetone, methyl ethyl ketone, methyl alcohol, isopropyl alcohol and trichloroethylene. However, kindly make sure that all the environmental, health and safety regulations are met prior to selecting a solvent. The most common methods used, typically include the three main steps:
  • Vapour degrease/clean/rinse the parts with the appropriate solvents
  • Immerse the substrates in a fresh bath of solvent for the wash and follow by an immersion in the second tank for a rinse
  • Cleaning and drying the substrate post the degreasing
Abrasion
 
Mechanical abrasion of smooth surfaces is employed in order to remove heavy loose surface deposits such as dirt, oxide layers or any other contaminants that might be deposited on the surface. Some of the most effective mechanical methods used include sand blasting, wire brushing and abrasion with sandpaper or emery cloth. The surfaces need to be degreased and cleaned before as well as after abrasion to remove any pre-existing contaminants on the surface. Once the surfaces have been abraded, they need to be degreased to remove the debris from abrasion.
 
Dry abrasion is a mechanical technique where the operator hand sands or wire brushes the substrate with a medium abrasive material. But, this technique is highly dependant on the user and care should be taken to achieve consistent results. Abrasive blasting tends to be preferred as it is a fast, efficient and highly controlled technique. Sand blasting or other techniques are typically employed to achieve this. An RMS of about 150 (microinches) to 250 (microinches) is generally recommended for metals. Please note caution must be exercised based on the exact material used eventually on the feasibility of this technique.
 
Chemical Treatment
 
Specific chemical techniques have been developed for treating different substrates. These treatments change the physical as well as the chemical properties of the surface in order to improve the adhesion. A wide range of acids and alkalis are used for this purpose. Typically the specific chemical or a mixture of chemicals is placed in a chemically resistant container. The chemical bath is then heated to the appropriate temperature and the metal is immersed in the chemical bath for the required amount of time. After chemically treating the surfaces, it is important to rinse the surface with DI water and thoroughly dry the surface before it is subjected to further use. Extreme care should be taken while handling of chemicals. Good laboratory skills should be used while handling these chemicals. The personnel should be wearing the appropriate personal protective equipment and should be well trained in handling of these chemicals.
 
Substrate Etching Solution Composition (Wt%) Pretreatment Conditions
Aluminium

Sulfuric Acid (96%)
Sodium dichromate

77.8
22.2

Immersion: 20 min. @ 25C 
Rinse: Tap water followed by DI water 
Oven Dry: 30 min. @ 70C
Beryllium Sulfuric Acid (96%)
Sodium dichromate
20.0
80.0
Immersion: 3-4 min. @ 79-85C
Rinse: Tap water followed by DI water
Oven Dry: 30 min. @ 70C
Copper
Nitric Acid (69%)
Ferric chloride
Distilled Water
12.4 
6.2
81.4
Immersion: 1-2 min. @ 21-32C 
Rinse: Tap water followed by DI water
Oven Dry: 30 min. @ 65C
Magnesium Chromic Acid 
Distilled Water
20.0
80.0
Immersion: 10 min. @ 71-88C
Rinse: Tap water followed by DI water
Oven Dry: 30 min. @ <60C
Nickel Nitric Acid (69%) 100.0 Immersion: 5 sec. @ 20C
Rinse: Tap water followed by DI water
Oven Dry: 60 min. @ 40C
Stainless Steel Nitric Acid (69%)
Distilled Water
20.0
80.0
Immersion: 25-35 min. @ 21-32C
Rinse: Tap water followed by DI water
Oven Dry: 30 min. @ 65C
Steel (mild) Ethyl alcohol (denatured)
Orthophosphoric Acid (85%)
66.7
33.3
Immersion: 10 min. @ 60C
Rinse: Tap water followed by DI water
Oven Dry: 60 min. @ 120C
Titanium Nitric Acid (69%)
Hydrofluoric Acid (60%)
Distilled Water
28.8
3.4
67.8
Immersion: 10 - 15 min. @ 38-52C
Rinse: Tap water followed by DI water
Use a nylon brush to brush off residual carbon while rinsing 
Oven Dry: 15 min. @ 70C
Zinc Hydrochloric Acid (37%)
Distilled Water
20
80
Immersion: 2-4 min. @ 20C
Rinse: Tap water followed by DI water
Oven Dry: 30 min. @ 70C

 

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