Aluminum epoxy joints

Fig. 6. Shear strength of aluminum/epoxy joints and tensile strength of epoxy resin after exposure to water and ethanol at 90 °C 66) (Reprinted from Ref. 66, p. 63, by courtesy of Society of Chemical Industry)...

Aluminum/epoxy joints formed using FPL treated substrates exhibit very good initial adhesion strength. In addition, the FPL process is significantly easier to perform than the anodizing pretreatments. Therefore, if the FPL process could be modified so that the oxide layer produced is protected from hydration, it could once again become the pretreatment of choice for aluminum substrates. 

FIGURE 15.18 Effect of surface pretreatment on the durability of aluminum-epoxy joints subjected to accelerated aging in water at 50°C.59... 

A further enhancement in aluminum/epoxy joint durability in a moist environment is obtained by anodizing the aluminum after FPL treatment (80). Typically, samples are anodized for several minutes in an aqueous solution of phosphoric acid (phosphoric acid anodization or PAA) before rinsing and drying in warm air. The process produces a thin, uniform oxide layer near the bulk metal and a... 

In order to have a durable joint, it is necessary that the interfacial region maintain its mechanical integrity upon exposure to moisture. Davis and Venables have shown that the primary mechanism for degradation of strength of an aluminum-epoxy joint during moisture aging is the conversion of the oxide to boehmite, AlOOH, which apparently is weakly bonded to the base metal. AES analysis of joints broken after exposure to high humidity has shown that fracture occurs at or near the boehmite-metal interface. ... 

Ceiresien Resistance. Migration of water to adhesive joints is the most common form of bond degradation. Figure 7 conqrares the loss of strength in aluminum-epoxy joints after exposure in a hot-wet environment with the excellent durability that can be achieved under dry conditions. 

The effect of a multicomponent silane primer on the interphase structure of aluminum/epoxy adhesive joints... 

The primer chosen for this investigation consisted of an equimolar mixture of phenyl- and amino-functional silanes, suggested as a potential superior primer for aluminum/epoxy adhesive joints [7], The amino-functional silane is known to be effective as an adhesion promoter for fiber-reinforced composite materials [1, 2] as well as for epoxy/metal adhesive joints [8, 9] and provides for strong chemical interaction between the adhesive and primer, while the phenyl functional silane should reduce the overall concentration of polar, hydrophilic functional groups in the interphase region and at the same time maintain or improve the ability of the resin and primer to interpenetrate due to its structural similarity to the adhesive resin. 

FIGURE 15.17 Effect of adhesive on the durability of etched 6061-T6 aluminum alloy joints exposed to a marine environment. (1) Two-part epoxy, (2) one-part epoxy, (3) nitrile-phenolic, (4) vinyl-phenolic, (5) vinyl-phenolic.33... 

A number of techniques have been developed to convert corrosion-prone, clean surfaces to less reactive ones. Three common conversion processes are phosphating, anodizing, and chromating. These processes remove the inconsistent, weak surface on metal substrates and replace it with one that is strong, permanent, and reproducible.58 Figure 15.18 shows the effect of various pretreatments on the durability of aluminum alloy-epoxy joints subjected to aging in water at 50°C. 

TABLE 16.3 Effect of Surface Treatment on Aluminum Alloy Joints Bonded with a Heat Cured Epoxy Adhesive (EC-3443, 3M Company)6... 

Figure 5. The tensile shear strength of the composite aluminum-epoxy adhesive-polyethylene-epoxy adhesive-aluminum plotted as a function of the temperature of the joint formation...

Since the bubble chamber will be used with both hydrogen and helium, samples of aluminum epoxied to Plexiglas have been cycled to liquid-helium temperature several times with no visible degradation of the epoxy joint. 

The main limitation of this seal is that the epoxy joints slowly degrade after 6 to 8 cycles and the epoxy joint may loosen from the window. The aluminum seals, however, have been easily re-epoxied to the window wdth good success. 

Table 10.4 Effects of Surface Treatment on the Durability of 6061-T6 Aluminum Alloy Joints Exposed to Immersion in the Unstressed Condition (Nitrile-Modified Epoxy Paste Adhesivey ...

Aluminum/Epoxy Adhesive Joints", J. Adhesion 24, 313-335 Qndrus, D. J., Boerio, F. J., Gkannen (1989), "Molecular Structure of... 

R. G. Dillingham and F. J. Boerio, Interphase composition in aluminum/epoxy adhesive joints, J. Adhes. 24, 315 (1987). 

In a study of aluminum-epoxy adhesive joints, Dillingham and Boerio" used XPS analysis to determine that, after humid aging, the locus of fracture was within the metal oxide. They further proposed that catalysis during setting by acidic hydroxyls on the oxide caused the epoxy near the oxide to be more crosslinked than the bulk epoxy network. Another researcher" showed that fracture progressed within a weak boundary layer when a polyvinylidene fluoride-nylon bond was ruptured. 

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