Application of phase shifting interferometric microscopy to studies of the behaviour of coarse intermetallic particles in 6056 aluminium alloy

Phase shifting interferometric microscopy was used to study the behaviour, in sulphate solutions, of the two types of coarse intermetallic particles present in the 6056 T6 aluminium alloy. The influence of overaging was determined. The two types of particle did not present the same behaviour: the Al-Mg- and Si-containing particles dissolved during polarization in a sulphate solution, whereas the Al-Si-Mn- and Fe-containing particles led to the dissolution of the surrounding matrix. The behaviour of the coarse particles depended on the time of overaging: for the shortest time, the dissolution of the Al-Mg- and Si-containing particles was very strong; in the same way, the cathodic behaviour of the Al-Si-Mn- and Fe-containing particles was very significant. On the contrary, for the non-overaged 6056 T6 alloy, these two phenomena were not so significant. (C) 1998 Elsevier Science Ltd. All rights reserved.