Microstructure Characterization and Mechanical Properties of a Friction Stir Additive Manufactured (FSAM) AA6061 Bulk Material
By Jong-ning Aoh (National Chung Cheng University), Chih-wei Huang (National Chung Cheng University), Yong-fong Huang (National Chung Cheng University), Yu-an Huang (National Chung Cheng University)

A solid state friction stir additive manufacturing process (FSAM) was developed to produce an AA6061 bulk material by consecutive friction stir lap welding of stacked AA6061 plates. AA5083 was chosen as bottom plate so that the characteristics of material flow between stacking layers can be better visualized under macro etching of dissimilar aluminum alloys. Appropriate tool design and process parameters were relevant for a successful FSAM of defect-free bulk material. Material flow characteristics such as onion rings in the stir zone, hooking phenomenon and the associated kissing bond occurred on both sides of the TMAZ were of particular interest. Mechanical properties were determined by tensile test, hardness and shear test. Kissing bond and integrity of the bulk material can be unveiled by shear test using slotted specimens. Recrystallization and microstructure refinement within additive stir zone were characterized using OM, SEM and EBSD. T6 heat treatment was conducted to recover the strengths of the bulk pieces.