Characterization of Surfaces Prior to Adhesive Bonding.
Final rept. 15 Mar 75-15 Mar 76,
NORTHROP CORP HAWTHORNE CALIF AIRCRAFT DIV
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The objective of this program was to develop procedures for the quality control of anodized surfaces on aluminum alloys prior to bonding. The scanning electron microscope SEM was selected as the inspection instrument. Both phosphoric and chromic acid anodizing systems were included in the initial phases of this program. The character of these anodic surface coatings was evaluated on both bare and clad 7075-T6 in terms of physical, chemical, and crystallographic nature. Anodic coatings were found to be composed of a porous oxide layer of the boehmite or alpha-Al2O3.H2O crystallographic form. Panels anodized on both the PABST Primary Adhesively Bonded Structures Technology program at McDonnell Douglas and Phase II of Characterization of Surface Prior to Adhesive Bonding at Rockwell Science Center, exhibited oxide coatings of similar character. The dependence of the anodic film character on the various anodizing parameters was determined for the phosphoric acid anodizing of bare 7075-T6. Included in this investigation were anodizing variables such as voltage, time, bath concentration, Pretreatment prior to anodizing, and postanodize rinsing. Both thickness and cell size of the oxide layer were found to vary almost linearly with the anodizing voltage and parabolically with anodizing time. The oxide character was also found to vary with the concentration of the anodizing bath, with an increase in bath concentration resulting in increases in both oxide thickness and cell size. The anodic surface character determined by SEM inspection prior to adhesive bonding was correlated with the wedge test durability behavior of the bonded surface.
- Metallurgy and Metallography
- Fabrication Metallurgy
- Test Facilities, Equipment and Methods