Precipitation and crystallographic relationships of nanosized η/η’ precipitates at S-Al interface in Al-Zn-Mg-Cu alloy

Abstract

Quench-induced S(Al 2 CuMg) phases are generally formed in Al-Zn-Mg-Cu alloys. The precipitation and relative crystallographic relationships of η-type (MgZn 2 ) precipitates at the interfaces between the quench-induced S phases and Al matrix were studied in an Al-Zn-Mg-Cu alloy by coupling Cs-corrected scanning transmission electron microscopy (STEM) with scanning precession electron diffraction (SPED) technology. It was found that Zn segregation occurred at S-Al interfaces due to higher lattice strain energy, which induced the heterogeneous nucleation of nanosized η’ precipitates at these interfaces. Crystallographic orientation relationships (ORs) between the S phases and η’/η precipitates were firstly reported and discussed in Al-Zn-Mg-Cu alloy. With the coarsening of η precipitates at S-Al interfaces, a new type of OR ([112] Al //[ 1 ¯ 2 1 ¯ 0] η , (11 1 ¯ ) Al //(10 1 ¯ 3) η ) between the interfacial η precipitates and Al matrix was identified, which was different from their non-interfacial counterparts in Al matrix reported to date.