Correlation of Microstructure and Local Mechanical Properties Along Build Direction for Multi-layer Friction Surfacing of Aluminum Alloys

Abstract

The process variant of friction surfacing (FS) depositing multiple layers on top of each other is known as multi-layer friction surfacing (MLFS). Due to the solid-state nature of the process, re-heating is significantly reduced compared to common fusion-based AM techniques. The work gives a detailed and fundamental insight into the microstructure along the MLFS build direction for two different aluminum alloys and different process parameters. Focusing on the grain size distribution and recrystallization ratio, the stacks show a higher degree of recrystallization and finer grains at the interfaces. The observed grain sizes at the interfaces were 2.0 µm (AA5083) and 1.1 µm (AA2024), and 5.8 µm (AA5083) and 3.1 µm (AA2024) at the layer center. For the non-precipitation-hardenable alloy (AA5083), the local microstructural trend could be related to the hardness distribution along the stacks, i.e., a slightly higher hardness at the layer interfaces (95 HV) compared to the layer center (90 HV). The relationship is more complex for precipitation-hardenable alloys (AA2024), which show a rise in hardness between 40 HV0.2 and 45 HV0.2 along the stack height. The effect of subsequent layer depositions on the microstructure and hardness is discussed and a distinctive grain size distribution along the build direction was shown to be a fundamental characteristic.

Corrosion behavior of multi-layer friction surfaced structure from dissimilar aluminum alloys

“…The deposited material presents almost equiaxed grains with 3.28 ± 1.83 µm. For similar process parameters and materials, Shen et al 10 reported average grain size values between 4.0 µm and 4.7 µm, which is in good agreement with Kallien et al 31 as well as the results of this study. The grain size within a MLFS stack is relatively homogeneous for every layer 10 .…”

“…The consumable stud base material and MLFS deposited material did not present a difference in chemical composition for EDS analysis, but the materials are microstructurally distinct 31 , Fig. 3 .…”

“…The grain size within a MLFS stack is relatively homogeneous for every layer 10 . Slight alterations in grain size are linked to the complex material flow during FS layer deposition, leading to local fluctuations in plastic strain and temperature conditions 31 .

Figure 3 Micrographs, ( a.1,b.1,c.1 ) etched (Barker’s solution of HBF 4 ) and ( a.2,b.2,c.2 ) from electron backscatter diffraction (EBSD), for the microstrutctual analysis of ( a ) AA5083 MLFS deposited material, ( b ) AA2024 substrate material and ( c ) AA5083 stud base material.

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