Microrough morphology

In characterizing adherend morphologies, we will use the terms microrough and macrorough. The distinction between the two is arbitrary however, for discussion purposes, a microrough morphology is characterized by features with dimensions on the order of tens of nm. The term macrorough is used to characterize features with dimensions on the order of microns. 

Aluminum surfaces are prepared for adhesive bonding in aerospace applications by either etching or anodization in acid solutions. (For less stringent strength and durability requirements, mechanical abrasion can be adequate.(2)) Common preparations result in microrough adherend morphologies, which studies have shown yield the best overall bond durability. Three of these surface preparations are described in this section Forest Products Laboratory (FPL) etching procedure, phosphoric acid anodization (PAA), and chromic acid anodization (CAA). 

The FPL oxide morphology is shown in the high-resolution SEM stereo micrograph and isometric drawing in Figure 2.(i2) The oxide consists of a network of shallow pores and protrusions or whiskers on top of a thin, barrier layer. This microroughness provides a... 

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