Investigation of friction surfacing of an Al-Mg alloy in view of solid-state additive manufacturing
von Zina KallienFriction surfacing (FS) is a solid-state layer deposition technique for metallic materials, where
the deposition of a consumable material is enabled due to friction and plastic deformation. The
principle shows potential as coating technology, repair technique or additive manufacturing
(AM) approach. Major advantages lie in the solid-state nature of the FS process as the layer
deposition is performed below materials’ melting temperature. This avoids challenges that are
common for fusion-based processes, which are mainly related to material melting and solidification,
as for example porosity or hot cracking. Additionally, lower thermal gradients are
induced, preventing strong anisotropy and distortion. FS can be performed for various material
combinations, including some of those that are considered to be non-weldable via fusion-based
approaches. Despite the broad potential of the FS technique, the fundamental knowledge about
the process-controlling parameters and the properties of the deposited material show significant
research gaps. This work approaches these gaps on the example of an Al-Mg alloy.
The aim of this study is to explore material properties and potential applications of FS, in
particular as AM approach. In the first part, an extensive parameter study is performed for
single layer FS deposition with regard to process temperature and resulting geometry of the
deposit. The experimental data is used to set up and validate a numerical heat transfer model
based on the finite element method that provides high resolution temperature distributions as
well as the temperature evolution during the FS deposition process within the substrate. The
obtained results point to a direct relation between deposit geometry and process temperature.
The findings open new options to control and/or optimize layer deposition via FS as active
heating or cooling is expected to influence the layer deposition.
The second part of this work focuses on the characterization of the properties of FS deposited
material for multi-layer FS structures. The built structures are used for extensive analyses of
the microstructure as well as the mechanical properties with special focus on the role of layer
interfaces. The results revealed a significantly refined microstructure enabled by recrystallization,
which presents a periodic trend in grain size along the build direction, i. e. height of the
build stacks. The observed microstructural features were found to be a fundamental characteristic
of FS depositions, which are in correlation with the corresponding hardness distribution
of the stack built from a non-precipitation-hardenable Al-Mg aluminum alloy. In terms of
tensile strength, the FS deposited material presents homogeneous strength and no significant
directional dependency or preferred interface where failure occurred for room temperature testing.
Compared to the base material, the FS deposited material showed an increased strength at
room temperature, which could be related to the Hall-Petch strengthening effect. Tensile testing
at elevated temperatures revealed homogeneous properties; however at high temperatures
of 500 ◦C, significant grain growth occurs, which affects the tensile behavior. Furthermore, the
layer interfaces were no found to have a significant effect on fatigue crack propagation at room
temperature, leading to the overall conclusion that the FS layer interfaces are not detrimental to
static and dynamic mechanical properties of the FS deposited structure at room temperature.
Overall, this work presents comprehensive insights into the properties of a FS deposited Al-Mg aluminum alloy. The obtained properties are very promising compared to other (fusionbased)
layer deposition techniques, underlining the potential of the FS process. The current
results present a basis for further research and optimization of FS deposited material advancing
towards the application.
the deposition of a consumable material is enabled due to friction and plastic deformation. The
principle shows potential as coating technology, repair technique or additive manufacturing
(AM) approach. Major advantages lie in the solid-state nature of the FS process as the layer
deposition is performed below materials’ melting temperature. This avoids challenges that are
common for fusion-based processes, which are mainly related to material melting and solidification,
as for example porosity or hot cracking. Additionally, lower thermal gradients are
induced, preventing strong anisotropy and distortion. FS can be performed for various material
combinations, including some of those that are considered to be non-weldable via fusion-based
approaches. Despite the broad potential of the FS technique, the fundamental knowledge about
the process-controlling parameters and the properties of the deposited material show significant
research gaps. This work approaches these gaps on the example of an Al-Mg alloy.
The aim of this study is to explore material properties and potential applications of FS, in
particular as AM approach. In the first part, an extensive parameter study is performed for
single layer FS deposition with regard to process temperature and resulting geometry of the
deposit. The experimental data is used to set up and validate a numerical heat transfer model
based on the finite element method that provides high resolution temperature distributions as
well as the temperature evolution during the FS deposition process within the substrate. The
obtained results point to a direct relation between deposit geometry and process temperature.
The findings open new options to control and/or optimize layer deposition via FS as active
heating or cooling is expected to influence the layer deposition.
The second part of this work focuses on the characterization of the properties of FS deposited
material for multi-layer FS structures. The built structures are used for extensive analyses of
the microstructure as well as the mechanical properties with special focus on the role of layer
interfaces. The results revealed a significantly refined microstructure enabled by recrystallization,
which presents a periodic trend in grain size along the build direction, i. e. height of the
build stacks. The observed microstructural features were found to be a fundamental characteristic
of FS depositions, which are in correlation with the corresponding hardness distribution
of the stack built from a non-precipitation-hardenable Al-Mg aluminum alloy. In terms of
tensile strength, the FS deposited material presents homogeneous strength and no significant
directional dependency or preferred interface where failure occurred for room temperature testing.
Compared to the base material, the FS deposited material showed an increased strength at
room temperature, which could be related to the Hall-Petch strengthening effect. Tensile testing
at elevated temperatures revealed homogeneous properties; however at high temperatures
of 500 ◦C, significant grain growth occurs, which affects the tensile behavior. Furthermore, the
layer interfaces were no found to have a significant effect on fatigue crack propagation at room
temperature, leading to the overall conclusion that the FS layer interfaces are not detrimental to
static and dynamic mechanical properties of the FS deposited structure at room temperature.
Overall, this work presents comprehensive insights into the properties of a FS deposited Al-Mg aluminum alloy. The obtained properties are very promising compared to other (fusionbased)
layer deposition techniques, underlining the potential of the FS process. The current
results present a basis for further research and optimization of FS deposited material advancing
towards the application.