THE EFFECT OF MICROSTRUCTURE ON THE POLARIZATION AND STRESS CORROSION CRACKING IN AL-5MG ALLOYS

摘要

This paper presents a study of the microstructures of A1-5Mg alloys with additions of the alloying elements So, Zr, and Ag and the effects of these elements on the polarization and stress corrosion cracking behavior of this material in a 3.5%NaCI solution (pH=8) at 50°C. The results show that Sc+Zr additions have a stronger effect on inhibiting recrystallization than does Zr alone, and that in a sample aged for 24 hours the Zr+Sc alloy had less precipitation of AI3Mg2 along the grain boundaries relative to the alloy that contained only Zr additions. In the alloy that contained Ag and Zr additions, there was significantly more precipitation of A13Mg2 along the grain boundaries than in the aUoy that contained only Zr. Additions of Sc and Ag improve the protective nature of the passive film in A1-5Mg-0.15Zr alloys in 3.5%NaCI solution. Addition of Sc to an AI-5Mg-0.15Zr alloy improves stress corrosion cracking resistance, while addition of Ag causes the alloy to become more susceptible to stress corrosion cracking in the quenched (510°C) and aged (175°C/24h) conditions.