Investigation on Surface Hardness and Microstructure Evolution in AA ۷۰۷۵-T۶۵۱ Multi-Layered Laminate Fabricated Through Friction Stir Additive Manufacturing

Friction stir additive manufacturing (FSAM) is a variant of sheet lamination additive manufacturing used to produce large, near-net-shaped ۳D parts. Unlike traditional friction stir lap welding, FSAM introduces a new plate to one that is already joined, with the effective area limited to the nugget zone. The present study focuses on exploring the microstructure and microhardness around the nugget zone in a five-plate AA ۷۰۷۵-T۶۵۱ laminate synthesized at ۱۰۰۰ rpm and ۳۵ mm/min. Microhardness increased vertically in the weldment NZ, reaching ۱۴۳ HV in the top layer with ۲.۰ μm fine equiaxed grains. The grains on the advancing and retreating sides were coarser compared to the nugget zone. A W-shaped microhardness profile appeared across layer interfaces. These findings contribute significantly to advancing the FSAM technique, particularly in manufacturing multi-layered, multi-pass laminates.

Keywords:

Friction stir additive manufacturing (FSAM) , surface hardness , microstructure evolution , grain refinement , AA ۷۰۷۵-T۶۵۱