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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. b s t r a c tThe effect of prior work hardening on the microstructure and mechanical properties of a friction-stir welded (FSWed) Al-5.4Mg-0.2Sc-0.1Zr alloy was investigated. The microstructure of the final stir zone was shown to be weakly dependent on the initial condition of the base material; FSW led to the formation of fully recrystallized microstructures with average grain sizes ranging from 1.2 to 1.5 μm and a moderate dislocation density of $ 3.57 1.5 Â 10 13 m À 2 in the stir zone. The nano-scale Al 3 (Sc,Zr) dispersoids coarsened from 9 to $ 15 nm but retained a coherent relationship with the matrix. In contrast, the joint efficiency of the obtained welds was very sensitive to the initial material condition. Nearly full strength joints were obtained in both annealed (O) and partially hardened and stabilized (H323) conditions. However, the joint efficiency was only 65% in the fully hardened condition (H18). The relatively low weld strength for the alloy in the H18 condition was attributed to the elimination of dislocation and substructure strengthening during FSW.

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