Galvanized steels, bonding

Fitzpatrick et al. [41] used small-spot XPS to determine the failure mechanism of adhesively bonded, phosphated hot-dipped galvanized steel (HDGS) upon exposure to a humid environment. Substrates were prepared by applying a phosphate conversion coating and then a chromate rinse to HDGS. Lap joints were prepared from substrates having dimensions of 110 x 20 x 1.2 mm using a polybutadiene (PBD) adhesive with a bond line thickness of 250 p,m. The Joints were exposed to 95% RH at 35 C for 12 months and then pulled to failure. 

Fitzpatrick and Watts [57] also applied imaging TOF-SIMS to deteiTnine the failure mechanisms of adhesively bonded, phosphated hot-dipped galvanized steel... 

These results demonstrate some interesting chemical principles of the use of acrylic adhesives. They stick to a broad range of substrates, with some notable exceptions. One of these is galvanized steel, a chemically active substrate which can interact with the adhesive and inhibit cure. Another is Noryl , a blend of polystyrene and polyphenylene oxide. It contains phenol groups that are known polymerization inhibitors. Highly non-polar substrates such as polyolefins and silicones are difficult to bond with any technology, but as we shall see, the initiator can play a big role in acrylic adhesion to polyolefins. 

Initial bond strength depended heavily upon substrate type rather than surface preparation. Regardless of pretreatment, initial bond strength was highest when using Al-Tl adherends and lowest when the adherends were galvanized steel. 

Typical bond performance of adhesives of the first generation type is shown in Table 2. The adhesives have good adhesion to thermoplastics such as polystyrene, ABS, and poly(vinyl chloride), to wood and rubber, and to steel and aluminum provided the metals are clean. It can also be seen from this table that adhesion to galvanized steel is lower than to other metals. Bonding to galvanized steel was a problem with first generation acrylic adhesives but it has been overcome with more recent embodiments of this technology covered later in this chapter. 

Adhesives of HP type have been shown to bond bronze, lead, nickel, magnesium, copper, aluminum, steel, and stainless steel, in addition to most of the other substrates that earher offerings were capable of bonding. They did, however, continue to show weaknesses when zinc surfaces were bonded. So these adhesives may not be well suited for certain appKcations in the automobile area where galvanized steel is being bonded (Note that later generations covered in this chapter do not necessarily have this shortcoming). 

D. J. Damico, Bonding galvanized steel with RT curing acrylics. Adhesives Age Oct. (1987). D. J. Damico, Putting today s new structural adhesives to work for you. Design News, June 67-68 (1991). 

The chemical reactions of cement paste with zinc (galvanized steel) result in the release of zinc to the solution and the formation of calcium zincate, CaZn2(OH)g 2H2O, covering the surface of metal [49], Simultaneously, there is no portlandite crystals in this transition zone because in the presence of zinc alite hydration is delayed (see Sect. 4.1.3.2). The coating of hydrated calcium zincate crystals on the surface of metal increases the bonding forces between paste and reinforcement by the roughness formation on its surface. 

Fig. 1.17 NMP test of automotive epoxy-polyurethane primer on hot dip galvanized steel, (a) Test coating, (b) Influence of silanes in reinforcing interface bonding secondary bonds are converted to primary covalent bonds (Van Eijnsbergen).

Figure 113 Wooden steps covered with (bonded) aluminum chequerplates fastened by elastic adhesive onto the galvanized steel frame.

For electrical safety reasons, the telecommunication cable plant has to be grounded and bonded. This means that some bare metallic components of the plant have to be directly exposed to corrosive environments. Some of these alloys are not particularly corrosion resistant, and at some locations they require corrosion-control measures. An example of such a condition is where the galvanized-steel support hardware is part of the ground in a flooded manhole. 

The primary structure of the Z1 is galvanized steel, so in this respect the design of this plastic car is orthodox. However, the body platform whieh forms part of this primary structure is plastic, and therefore broke new ground. Essentially this is made up of a PUR foam core, sandwiched within glass mat which is then impregnated with a foamed epoxy resin. The Z1 is bonded together by robots, but the cost of its specialized composite structures eliminates any possibility of this route being followed in a volume car. 

R. T. Fbister, Adhesive bonding to galvanized steel, II. substrate chemistry, morphology, and bond failure analysis, J. Adhes. 24, 279 (1987). 

Plasma polymers with a special surface structure suitable to bond to an epoxy amine primer were used as interfecial coupling layers on iron and galvanized steel and led to even better results [122]. However, in all cases the system always showed cathodic delamination at the polymer/metal oxide interface, indicating the importance of oxygen reduction on the oxide surface. For verification, after the delamination of the sample, the delaminated polymer was pulled off and the underside of the polymer and the iron surface were investigated by XPS to reveal whether the system delaminated at the plasma polymer/metal interface or at the... 

The development of SPM and particularly AFM has not been ignored by the adhesion world. The analysis of failure surfaces by AFM is still in its infancy but it is already clear that AFM may sometimes be more useful than SEM. Thus AFM has been used successfully in the analysis of the failure surfaces of adhesively bonded galvanized steel [149] and in the study of the adsorption of polymers on conducting polymer substrates [150,151]. Some of the author s unpublished studies have shown that the corona treatment of polyolefines gives rise to a characteristic morphology and that failure interfaces from peel joints of polyolefine substrates can yield more useful information from AFM than from SEM investigations [152]. 

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