Pre-treatment of metals prior to bonding

Conversion coatings, commonly used in Pre-treatment of metals prior to bonding, are formed by a chemical reaction between an aqueous media, usually containing soluble metal salts, and a substrate to produce an insoluble passivating film. They may be chemical or electrochemically produced when produced with an externally applied voltage, an anodic oxide is formed (see Anodizing). 

Further information is given in articles on Pre-treatment of metals prior to bonding, Durabiiity creep rupture, Durabiiity subcritical debonding. Weathering of adhesive joints and Weathering tests. 

In the study of bond durability under impact conditions. Pre-treatment of metals prior to bonding and environmental effects have been evaluated using short diffusion path specimens derived from thin sheet adherend materials. The results (see Fig. 2) serve to emphasize the critical role of surface treatment in the formation of strong, environmentally stable adhesive bonds. 

The article. Pre-treatment of metals prior to bonding, provides a general survey this article is concerned with the industrially important aluminium and its alloys. 

Careful surface preparation before adhesive application is essential for consistent and successful bonding to most substrates (see Pre-treatment of metals prior to bonding), and this certainly applies to copper, which has a reputation for being difficult to bond. Part of the difficulty is the friability of the black copper(ll) oxide, which forms on the surface in air at temperatures in the range 200-500 °C. At ambient temperatures, a thin layer of copper(I) oxide is present. 

After Pre-treatment of metals prior to bonding, it may be several weeks before the adhesive is applied. Most pre-treated surfaces are stable for considerably less than 24 h, so protection by priming is needed. However, the effectiveness of primers, particularly of the corrosion inhibiting primers, can be very sensitive to coating thickness a change in thickness from 2-5 ftm to above 8-10 p.m can halve the peel performance of some adhesives. 

Good surface preparation is important in this context (see Pre-treatment of metals prior to bonding), as in most examples of adhesive bonding, as it influences the durability of the bond, especially in wet areas (see Durability - fundamentals). 

For further information, see the articles Rubber to metal bonding - basic techniques. Rubber to metal bonding - testing, Degreasing and Pre-treatment of metals prior to bonding. 

The more common environmental problem with metal joints is attack by water. In addition to alloy composition, pre-treatment and primer, durability is affected by the adhesive used (see Pre-treatment of metals prior to bonding. Pre-treatment of polymers. Primers for adhesive bonding). Sell has ranked adhesives in the order of durability they provide with aluminium substrates ... 

Almost always the Pre-treatment of metals prior to bonding is essential to the successful use of adhesives. A more general discussion of Primers for adhesive bonding is given elsewhere this article, which complements Silane adhesion promoters, provides detailed discussion of this important class of materials. 

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