Al合金単結晶の応力腐食割れにおける割れ先端の溶解電流について

Abstract

The stress corrosion cracking (SCC) test of Al-4%Cu single crystals was firstly carried out at various potentials in 5.7%NaCl+0.3%H2O2 solution, and secondly the SCC test of Al-4%Zn single crystals was carried out without applying potential in 5.0%NaCl+0.5%HNO3+0.3%H2O2 solution. The characteristics of SCC were analyzed by the mechanochemical mechanism proposed by Ohtani and Hayashi previously. The results obtained are as follows:(1) SCC of Al-4%Cu single crystals occurs due to preferential attack along (100) traces at any anodic potential. Fracture time decreases exponentially with an increase of potential.(2) SCC of Al-4%Zn single crystals occurs along (100) traces at the stress region below the yield point, but the orientation of cracking is not clear in the stress region above the yield point.(3) The stress dependence of cracking propagaion period for both single crystals is explained by a mechanochemical model in which the dissolution process at the tip of crack is rate determining.(4) There is a relation, i∝t, between the dissolution current (i) of newly created slip plaines at the tip of crack and time (t).(5) ε1⁄2⁄t (ε: strain) is nearly proportional to applied stress (σa). This means that the mechanochemical model mentioned above is valid for the SCC of both aluminum alloy single crystals.