Comparative study of process characteristics and coating properties of Al-alloys 6082 and 5083 during Friction Surfacing

Tobias Bucken, University Duisburg-Essen, Duisburg, Germany
Jorge dos Santos, Helmholtz-Zentrum Geesthacht, Geesthacht, Germany
Alfons Fischer, Universität Duisburg-Essen, Duisburg, Germany
Stefanie Hanke, Helmholtz-Zentrum Geesthacht, Geesthacht, Germany

Friction Surfacing (FS) is a solid state joining process which enables the deposition of a coating layer. A rotating stud from the coating material is pressed onto the substrate under axial load, leading to heat generation in the stud tip and plastification of the material. The involved plastic deformation under high temperature (≈0.75Tmelt) and pressure leads to dynamic recrystallization of the coating material and initiates the bonding with the substrate. A high cooling rate (≈30K/s) retains the recrystallized microstructure and causes small grain sizes. A superimposed translational movement determines the direction of material deposition, during which the stud is continuously consumed.

The aluminium alloys 6082 and 5083 have been processed within the process parameter window as follows: rotational speed 1000–2000 min-1, axial force 9–16 kN, translational speed 2.5–15 mm/s. The material yield, the coating geometry, the process torque and temperature were analysed for both alloys. Further, recrystallization grain size and hardness were determined. Materials based on the same major alloying elements can behave quite differently during FS due to their specific mechanical and thermal properties. This study was carried out in order to analyse and compare the precipitation and the solid solution hardening alloys 6082 and 5083 with respect to their differences as to processing and microstructural characteristics.

Alloy 6082 can be processed in a wide parameter window, limited by 5083 which tends to discontinuities. At 2000 min-1, 9 kN and 15 mm/s, 6082 shows a coating thickness of more than 3.5 mm, whereas 5083 reaches only 1 mm. The material yield of 6082 with about 65% is twice as big as that of 5083. Temperature measurements show that 5083 renders higher temperatures up to 515°C compared to 6082. This is in agreement with a 30% bigger torque measured with 6082. The recrystallization grain size shows values between 5–20 µm for 5083, while the 6082 reveals also smaller ones of less than 5 µm. In comparison to the base material, the 6082 coating shows a decrease of hardness of 20 %, whereas the hardness of 5083 displays only little variations. As expected FS leads to a partial dissolution of precipitations for 6082, while the solid solution hardening of 5083 is not affected.

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