Design of hydrogen embrittlement resistant 7xxx-T6 aluminum alloys based on wire arc additive manufacturing: Changing nanochemistry of strengthening precipitates
Mahdieh Safyari, Martin Schnall, Fabio Haunreiter, Masoud Moshtaghi
Abstract
In this work, atom probe tomography technique is used to investigate how wire arc additive manufacturing (WAAM) changes the nanochemistry of nanoprecipitates and grain boundaries after peak aging of a high strength Al-Zn-Mg-Cu alloy. The effect of change in nanochemistry of nanoprecipitates on the hydrogen embrittlement of the additively manufactured aluminum alloy is investigated using a three-point bending test in humid air. The results show that the unique in-process heat treatment during WAAM, offers the possibility to modify the nanochemistry of nanoprecipitates and improve the hydrogen embrittlement of the Al-Zn-Mg-Cu alloys in the peak aged state without sacrificing mechanical performance. Density functional theory shows that the WAAM process transforms the interfaces between matrix and precipitate into a strong hydrogen trap, which can reduce the hydrogen content of grain boundaries and suppress hydrogen-induced intergranular fracture.