THE INFLUENCE OF ION-INDUCED SURFACE MODIFICATION ON STRESS-CORROSION CRACKING OF ALUMINUM-ALLOYS

There have been very few studies on the effect of ion beam treatment on stress corrosion cracking. Therefore ion implantation of Mg, ion beam mixing of Zr thin films and ion-beam-assisted deposition of Si were used for modifying the surface of aluminium alloys and pure aluminium. Corrosion measurements under pitting conditions and stress corrosion conditions were performed. Auger electron spectroscopy depth profiling and electron diffraction were used to determine the composition and structure respectively of selected samples. The stress corrosion samples were made of Al alloy 7475 T651 according to DIN 50 125. For the pitting measurements polished pieces of an Al rod with a purity of 99.5% were used. The pitting measurements were performed in aerated aqueous solution of 2% NaCl at 25-degrees-C. The resistance against stress corrosion cracking was measured using a method according to ASTM G44, i.e. alternating immersion in an aqueous solution containing 3.5% NaCl under a constant strain of 100 MPa. The results of the measurements showed that it is possible to inhibit the initiation of stress corrosion cracking of Al alloys for a prolonged period by application of several different ion-induced surface modifications. Under the given conditions it seems that pitting is not a prerequisite for stress corrosion cracking.