Fig. 4

(a) Macrograph of the AA6061-T6 FSLW cross section with white rectangles indicating typical regions; (b) a magnified view of the hook defect zone at AS in (a); a magnified view of (c) the upper and (d) the lower part of hook defect zone in (b); (e) a magnified view of the defect at RS in (a); (f) a magnified view including the kissing bonding defect and partial SZ in (a).