Structure-properties relations in spot friction welded (also known as friction stir spot welded) 6111 aluminum

D. Mitlin, V. Radmilovic, T. Pan, J. Chen, Z. Feng, M. L. Santella

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144 Scopus citations

Abstract

This work details some aspects of the microstructure-properties-processing relations in spot friction welded (also known as friction stir spot welded) 6111 Al sheets, joined in a lap configuration. We have shown that the tool pin penetration depth has a strong effect on the failure mode of the joined samples and a lesser effect on the joint shear strength. With increasing tool pin penetration depth, and consequently with increasing depth of the tool shoulder pressing into the top sample, the failure mode in a lap-shear test changes from brittle and concentrated near the pin hole, to ductile and away from the weld towards the base metal. The sheet interface under the tool shoulder consists four regions; a region where there is no contact at all between the two surfaces, a region where only a mechanical bond ("kissing bond") exists, a region where there is partial metallurgical bond, and a region with full metallurgical bonding. There is evidence that during welding the Fe-Si-Mn-Cu inclusions present in the as-received material are swept towards the joint interface, thus degrading the joint quality. The aluminum in the partially metallurgically bonded region, in the fully metallurgically bonded region and under the tool pin is fully recrystallized. In these regions, the presence of low angle grain boundaries indicates that additional deformation has occurred after recrystallized grains were formed. It is thus likely that recrystallization has occurred dynamically during the welding process. The material under the shoulder (a portion of the non-contacting region, the "kissing bond", the partial metallurgical and the full metallurgical regions) has a significantly larger grain size than under the pin, as well as a different texture.

Original languageEnglish
Pages (from-to)79-96
Number of pages18
JournalMaterials Science and Engineering: A
Volume441
Issue number1-2
DOIs
StatePublished - Dec 15 2006

Funding

This research was sponsored in part by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Freedom CAR and Vehicle Technologies, as part of High Strength Weight Reduction Materials Program under Contract DE-AC05-00OR22725 with UT-Battelle, LLC. Part of the microstructural analysis was performed at the National Center for Electron Microscopy (NCEM), LBNL, University of California, Berkeley. The NCEM is supported by the Director, Office of Science, U.S. Department of Energy under Contract No. DE-AC02-05CH11231. David Mitlin acknowledges Natural Sciences and Engineering Research Council (NSERC) of Canada and AUTO21 Network Centres of Excellence of Canada for sponsoring the research. The authors are grateful to Dr. S. Diamond's support. We are also grateful to A. Joaquin for cross-section specimens preparation.

FundersFunder number
Office of Freedom CarDE-AC05-00OR22725
U.S. Department of Energy
Office of ScienceDE-AC02-05CH11231
Office of Energy Efficiency and Renewable Energy
Natural Sciences and Engineering Research Council of Canada
AUTO21 Network of Centres of Excellence

    Keywords

    • 6111 Al alloy
    • Friction stir spot weld (FSSW)
    • Grain growth
    • Recrystallization
    • Spot friction weld (SFW)
    • Texture

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