Effect of Ga on Stress Corrosion Cracking Characteristics of Al-9 mass%Mg Alloys

Abstract

In the present investigation, precipitation behavior of a secondary phase by aging treatment, mechanical properties and time to stress corrosion cracking failure were measured and examined, for the purpose of determining the effect of Ga content on the stress corrosion cracking behaviors of Al-9 mass%Mg alloys in a mixed solution of 1 x 10 -2 kmol/m 3 HCl + 5 x 10 -1 kmol/m 3 NaCl including 3 x 10 -2 kmol/m 3 K 2 Cr 2 O 7 as an oxidizing agent. The principal conclusions are summed up as follows: (1) Stress corrosion cracking fracture resistance deteriorates with increasing Ga concentration in the alloys. Especially when the Ga component exists in the form of a solid solution, its effect is strong. The failure from stress corrosion cracking of the specimens in this investigation is primarily intergranular cracking. However, the aging treatment and the Ga content do not have considerable effects on the mechanical properties of the specimens. (2) The secondary phase precipitated in the specimens by the aging treatment consists of the Al 3 Mg 2 compound. However, in the specimens containing Ga, in addition to the Al 3 Mg 2 compounds, Ga compounds such as Mg2Ga and MgGa2 also precipitate. However, during the aging time shorter than 76.8 ks no no precipitation of the Ga compound was observed and the Ga component exists in the matrix as a solid solution.