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Aluminium and copper plates with 3 mm thickness were successfully friction stir lap welded at a lower rotation rate of 600 rev min 21 using a larger pin 8 mm in diameter. Good metallurgical bonding on the Al/Cu interface was achieved due to the formation of a thin, continuous and uniform Al-Cu intermetallic compound layer. Furthermore, many Cu particles consisting of pure Cu and intermetallic compound layers were generated at the lower part of the nugget zone, forming a composite structure with increased hardness. A lower rotation rate resulted in a decrease in annealing softening in the heat affected zone (HAZ), and a larger diameter pin increased the Al-Cu bonding area. These factors resulted in that the friction stir welded lap joint exhibited a high failure load of 2680 N with failure in the HAZ on the aluminium side.

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Cast Mg-Al-Zn (AZ80) alloy was subjected to friction stir processing (FSP) with three different FSP procedures: single pass, single pass with a pre-solution treatment (pre-ST), and two pass. FSP resulted in remarkable grain refinement, significant breakup, and dissolution of the coarse, networklike Mg 17 Al 12 phase. While the single-pass FSP procedure produced a heterogeneous microstructure with Mg 17 Al 12 particle-rich bands, both the pre-ST FSP and the two-pass FSP procedures resulted in the generation of a uniform microstructure. The pre-ST FSP and twopass FSP samples exhibited significantly enhanced strength and ductility due to remarkable grain refinement and dissolution of coarse Mg 17 Al 12 phase. A post-FSP aging resulted in the precipitation of fine Mg 17 Al 12 particle, thereby increasing the strength of the FSP samples. Among three FSP samples, the aged two-pass FSP sample exhibited the highest ultimate tensile strength (UTS) of 356 MPa and an elongation of 17 pct.