Summer Internship’23 Project: Synthesis of Functionally Gradient Material using Friction Stir Additive Manufacturing

FSAM is an additive manufacturing process based on friction stir processing (FSP). In this technique, a rotating tool plunges into the material layers, generating enough heat due to friction and causing severe plastic deformation, enabling material flow and joining metal layers. In this study, an Al-Cu-based functionally gradient material (FGM) with variation in mechanical and corrosion properties was introduced by stacking Al 6063 alloy sheets (0.7 mm thick) and copper powder. Stacking was done such that outer surfaces have Al alloy and the core region has a mixture of Cu and Al. It is expected that Cu addition will enhance the mechanical properties of the FGM, and outer Al alloy will help in improving corrosion resistance. FSP was performed at tool rotation speed of 600 rpm, traverse speed of 50 mm/min and tool tilt angle of 2˚. Microstructures were observed after sectioning the obtained FGM along the transverse plane. The samples were subsequently heat-treated (solutionised and peak-aged), and their corresponding hardness and corrosion properties were compared. Cu was dissolved in the Al matrix by solutionising. However, some Cu particles were visible, which indicates that solutionising conditions were insufficient. Partial dissolution of Cu was apparent since peak-aged samples had higher hardness due to the precipitates, while the dissolution of precipitates after solutionising resulted in low hardness.

The addition of copper enhanced corrosion resistance in the Al-Cu FGM, but the formation of new precipitates after solutionising and peak ageing led to a decrease in corrosion resistance due to micro galvanic coupling. Hardness: Peak-aged> Solution heat-treated > After FSAM > Base alloy Corrosion resistance: After FSAM > Peak-aged ~ Solution heat-treated> > Base alloy

The fabricated FGM showed ten times better corrosion resistance and higher hardness value than the base alloy. Also, it has better corrosion resistance than conventional Al-Cu alloys, which are highly susceptible to intergranular corrosion. Hence, our FGM has potential marine applications.