Joining AA7099 to Ni-Cr-Mo Steel Using Single Pass Friction Stir Dovetailing and AA6061 Butter Layer

Journal Article · Wed Jul 07 00:00:00 EDT 2021 · JOM. The Journal of the Minerals, Metals and Materials Society

DOI:https://doi.org/10.1007/s11837-021-04668-0· OSTI ID:1813582

Olszta, Matthew J.  ^[1]; Overman, Nicole R. ^[1]; Reza E Rabby, MD ^[1]; Roosendaal, Timothy J. ^[1]; Mcdonnell, Martin ^[2]; Whalen, Scott A. ^[1]

---

1. BATTELLE (PACIFIC NW LAB)
2. U.S. Army Tank Automotive Research, Development and Engineering Center

A novel single pass friction stir dovetailing (FSD) was developed to join thick plate AA7099 to Ni-Cr-Mo steel in a lap configuration through the use of an AA6061 butter layer. The butter layer approach can be shown to significantly reduce interfacial failures by inhibiting the formation of brittle Fe–Al intermetallic compounds (IMCs) which are typically formed during conventional friction stir welding (FSW) of AA7099 directly to steel. This study evaluates the strength and microstructural evolution of the aluminum/steel joint interface between single pass FSD of AA7099/AA6061(butter)/steel fabricated using three different FSD tool configurations. The butter layer was achieved by placement of a free-floating strip of AA6061 within the dovetail groove that was pre-machined in the steel substrate. Friction stir welding was then used to simultaneously join the thick plate AA7099, the AA6061 strip and the AA7099 in a single weld pass. To optimize the joining process, three different pin geometries (full thread, half smooth/half thread, no thread) were evaluated; it was demonstrated that the half smooth/half thread tool produced the strongest weld joint due to the absence of a Zn rich layer at the Al/steel interface. The efficacy of this unique processing technique was tested using lap shear tensile testing as well as high resolution transmission electron microscopy (TEM). A discussion of the new FSD technique, joint configurations, and process parameters are provided along with joint microstructural analyses and mechanical performance.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1813582
• Report Number(s): PNNL-SA-155286
• Journal Information: JOM. The Journal of the Minerals, Metals and Materials Society, Vol. 73, Issue 7
• Country of Publication: United States
• Language: English