Pretreatment, aluminum alloys surfaces

Figure 15. XPS carbon Is and oxygen Is photopeaks for pretreated aluminum alloy after acid etch and before bonding (FPL) two failure surfaces following bonding with polysulfone and testing in the wedge configuration (FPL MFS and FPL AFS) and, neat polysulfone (PSF) (38).

Aluminum. Eor aluminum alloys such as 1100 and 3003 only a cleaning operation is necessary before apphcation of enamel. Eor ahoy 6061, deoxidation and alkaline-chromate pretreatment processes may also be used to improve both the cleanliness of the surface and the development of enamel adherence. The spent chromium-containing solutions can present disposal problems and should be handled in accordance with existing regulations (19). 

Fig. 5. Effect of outdoor weathering on the strength of aluminum alloy/epoxy-polyamide joints (chromic-sulfuric acid-etch metal surface pretreat-ment)61 (Reprinted from Ref. 61, p. 194, by courtesy of Gordon and Breach...

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. 

A study of the pretreatment application and the surface prior to deposition indicates that the aluminum alloy panels have a marked sensitivity to the buildup of a fluorocarbon background in the plasma reactor. This study also showed that the application of the O2 plasma treatment modified the alloy surface, changing it... 

In this paper, we have presented test results of two methods of adhesion improvement on a specific aluminum alloy and a stainless steel. The methods are based on flame pyrolysis of silane precursors and a laser pretreatment in connection with a primer. While the first method seems to be most favorable for steel surfaces, the latter gives good results on both aluminum and steel. Both methods are well suited for application in the railroad industry since they are effective under atmospheric conditions and are therefore promising for integration in an automated production line. 

Lap shear tests were carried out using single lap joint specimens of the aluminum alloy (5052H34). Sample dimensions are shown in Fig. 34.6. Surface pretreatment and curing conditions of the joint specimens were similar to the other specimens used for the dismantlement test The lap shear strength of the... 

Figure 10.5 shows the data obtained on an epoxy-nitrile film adhesive on 5052-H34 aluminum alloy after immersion in hot water for 50, 100, 300, 500, and 1000 hours. This test is very useful because it permits a large number of adhesive-bonded specimens with different adhesives, adher-ends, and surface pretreatments to be tested at the same time with a relatively small investment in man hours and equipment. Figure 10.6 shows a comparison of the stressed-durability data and unstressed hot-water-soak data on the same epoxy-nitrile film adhesive, using 2024-T3 aluminum alloy. Note the parallelism of the plots. The curve in the lower left was obtained when lap-shear specimens were subjected to various levels of stress and then exposed to an environment of 60°C and 95% RH until failure. The failure time is plotted as a log function. The curve in the upper right portion is a plot of the data when the same types of lap-shear specimens were subjected to 60°C water for specified periods of time and then tested for their residual strength. In the first case, failure time was recorded. In the latter case, residual strength was determined. The same type of data is obtained with both curves. ... 

The effect of environment on pretreated oxides has also been studied by STEM. Venables et al.U ) documented the degradation mechanism causing bond failure of FPL (Forest Products Laboratory) etched aluminum alloys in a humid environment. The surface oxide with a cellular and whisker structure converts to a surface hydroxide with a com flake type stmcture as shown by a schematic diagram of the mechanism in Figure 15. 

In addition to specular reflectance, diffuse reflectance can also be used to study interfaces. Six compounds adsorbed on pretreated aluminum surfaces were studied by Kollek.(26) Figure 18 is the DRIFT spectrum of dicyandiamide in potassium bromide and adsorbed on CAA aluminum 2024-T3 clad alloy. The intensity of the nitrile peaks at 2207 and 2164 cm - in the dicyandiamide in a potassium bromide sample (upper spectrum) decreased in the dicyandiamide adsorbed onto CAA aluminum sample (lower spectrum), suggesting that a chemical reaction occurred between the nitrile group in the dicyandiamide and the aluminum oxide with new peaks resulting from this reaction assigned to an amide group. 

Like the aluminum alloys mentioned earlier, the titanium alloy surface can be pretreated by an anodizing process in which there is a controlled rate of surface dissolution accompanied by new oxide formation. Anodizing in bath solutions of either a chromic acid-fluoride or an alkaline-peroxide mixture produces joints with both high initial joint strength and long-term durability. 

The use of chemical pretreatments in acid or basic medium aimed to increase roughness and/ or to oxidize the alloy surface is less frequent [70,71], Aluminum slabs [72] or AISI316 stainless steel grids [70] have successfully been treated with acid aqueous solutions. However, attempts of chemical treatment of aluminum structured substrates lead to the dissolution... 

The surface pretreatment of aluminum alloys for adhesive bonding has been reviewed by Critchlow and Brewis (1996). The literature in the period 1976-1991 on the wet durability of aluminum joints bonded with epoxide adhesives has been reviewed by Armstrong (1997). Critchlow and Brewis (1995) have also reviewed surface treatments for the titanium alloy Ti-6Al-4 V. 

Figure 5.1 Effect of surface pretreatment on the performance of aluminum-alloy epoxy joints subjected to accelerated aging in water at 50 °C. ...

Surface characteristics and durability of adhesive bonded AA6060 aluminum alloy joints with different pretreatments have been studied. The results... 

---