Investigation of Cr, Cu and Zn sites in corroded/uncorroded aluminum by X-ray absorption spectroscopy (XAS)

X-ray absorption spectroscopy (XAS) was used to characterize the Cr, Cu and Zn sites in 7175 T736 aluminum which had exhibited corrosion at the bond between the Al and ethylene propylene diene monomer (EPDM) during 9.8 years of storage. The characterization was concerned with the Cr, Cu and Zn coordination chemistry (chemical valence, coordination number, bondlength, disorder, and species of surrounding atoms) of corroded and uncorroded samples. The results show that only the Cu site in the Al alloy significantly changed during the process of corrosion. After corrosion no chemical shift was observed in the Cu K-edge (8979 eV) nor was the significant presence of Cu oxide, sulfide, chloride or hydroxide found. Analysis of the data using XAS methods indicated that similar to 20% +/- 10% of the Cu sampled (to a depth of similar to 104 mu m using fluorescent yield) was present as disordered, metallic Cu after corrosion. The remainder of the Cu was present in the alloy as it would be found in uncorroded 7175 T736. Very little Cu was found in the top similar to.235 mu m of the corrosion layer as sampled by electron yield methods. (C) 1997 Elsevier Science Ltd.