Effect of second phase and grain boundary precipitation characteristics on intergranular corrosion properties of 7050 aluminum alloy

Abstract

SEM，EBSD and TEM techniques were used to study the effects of grain boundary precipitation characteristics and the Fe-containing second phase（Al7Cu2Fe phase） formed under different aging regimes on the intergranular corrosion properties of Al-Zn-Mg-Cu alloys. The results show that the change rate of Fe content of Al7Cu2Fe phase with large surface size of aluminum alloy specimen after aging at 120 ℃ for 24 h is the largest，while the phase change rates of Fe content of Al7Cu2Fe phase with small size in specimens aging at 120 ℃ for 60 h and 120 h are greater. With the increase of aging time，the corrosion time of surface pitting caused by Al7Cu2Fe phase in 7050 aluminum alloy specimen is shortened，and the depth of intergranular corrosion decreases，indicating that its intergranular corrosion resistance is enhanced with the increase of aging time. In addition，with the increase of aging time，the PFZ （precipitation-free zone） width of the sample increases，the number of nuclei of GBPs（grain boundary precipitation） decreases，the spacing between GBPs increases，and the grain orientation prone to intergranular corrosion is gradually concentrated.

Keywords

• al-zn-mg-cu alloy
• aging time
• intergranular corrosion
• al7cu2fe phase
• grain boundary precipitation characteristics