Mechanical interlocking aluminum

Since water exposure has been shown 86) to have no substantial short-term effect on adhesive bonds in which a large degree of mechanical interlocking is present, these pretreatments have the potential to enhance the durability of aluminum/polymer adhesion systems. 

One might expect that the more developed porous layer produced by the PAA process would tend to provide a greater number of successful mechanical interlocking sites 54-86-135-136> and initiate a larger degree of plastic deformation in the resin upon failure than the FPL oxide. Test data i29) comparing PAA and FPL pretreated systems have supported this conclusion. Also, the oxides formed by the PAA pretreatment have exhibited better stability in wet environments 54). Hence, the PAA process has replaced the FPL etch as the method of choice for the pretreatment of aluminum for adhesion systems i32-133>. 

T/F plasma polymer was also selected to improve the adhesion of different spray paints to IVD Al-coated panels. As presented in Table 32.3, T/F plasma polymer [DC plasma-polymerized trimethylsilane (TMS) followed by hexafluoroethane (HFE)] gave rise to such a strong adhesion of E-coat that could not be stripped off after 24-h application of Turco solution. Since the formation of mechanical interlocking between primers and porous IVD surfaces could conceal the role of plasma treatment in enhancing adhesion, bare 7075-T6 aluminum alloy panels with smooth surfaces were first used as substrate to examine the effect of plasma treatment on the adhesion of spray paints. 

Phosphoric acid anodization (PAA)( > is a common method of surface preparation of aluminum adherends prior to adhesive bonding for aerospace applications. PA A surfaces are microscopically rough(6) and are more resistant to hydration than aluminum surfaces prepared by other treatments.(2,90) The microroughness provides for mechanical interlocking with the primer or adhesive, which results in a strong adhesive bond, while the environmental stability of the oxide (together with its porosity) results in excellent bond durability in hot, humid environments. 

For example, chromate etching of aluminum, such as was used in this study, produces a porous outer layer of oxide which promotes adhesion through mechanical interlocking of adhesive and substrate ... 

---