Abstract
Aluminium alloys from the 6xxx series are used in numerous applications due to their versatile properties. Machinability is particularly important for the production of complex components. Bismuth is a promising alloying element for improving the machining properties of AlMgSi alloys. Due to the insolubility of bismuth in aluminium and the formation of low-melting phases, it promotes short chip breaking, which is crucial for efficient machinability.
This work aims to investigate the strength potential of a modified 6xxx aluminium alloy in which bismuth was used as a chip breaking element. Various alloy compositions were produced by Design of Experiment (DoE) and subjected to industry-standard heat treatment. Brinell hardness measurements were used to assess strength, while microstructural and chemical analyses using scanning electron microscopy were used to characterise the microstructure. Thermodynamic calculations and a linear regression model made it possible to analyse the influence of the alloying elements on the hardness and to predict future hardness values based on the composition.
The results illustrate the direct influence of the bismuth content on the hardness of the alloys analysed. Particularly in low-alloyed variants, a high bismuth content leads to a significant reduction in hardness. In higher alloyed alloys, this effect is less significant due to the larger volume of hardness-increasing phases. The formation of the β-Mg3Bi2 phase was identified as the main factor for the loss of hardness. This phase, which has no positive effect on machinability compared to the low-melting eutectic Bi + α-Mg3Bi2 compound, binds magnesium from the melt at an early stage. As a result, less magnesium is available for the formation of the primary hardness-increasing Mg2Si phase, which leads to a lower hardness. In order to avoid deviations in hardness, a targeted adjustment of the alloying elements, in particular magnesium and bismuth, is necessary.
These findings make an important contribution to the further development of aluminium alloys with improved machining properties that meet the requirements of modern production processes.
This work aims to investigate the strength potential of a modified 6xxx aluminium alloy in which bismuth was used as a chip breaking element. Various alloy compositions were produced by Design of Experiment (DoE) and subjected to industry-standard heat treatment. Brinell hardness measurements were used to assess strength, while microstructural and chemical analyses using scanning electron microscopy were used to characterise the microstructure. Thermodynamic calculations and a linear regression model made it possible to analyse the influence of the alloying elements on the hardness and to predict future hardness values based on the composition.
The results illustrate the direct influence of the bismuth content on the hardness of the alloys analysed. Particularly in low-alloyed variants, a high bismuth content leads to a significant reduction in hardness. In higher alloyed alloys, this effect is less significant due to the larger volume of hardness-increasing phases. The formation of the β-Mg3Bi2 phase was identified as the main factor for the loss of hardness. This phase, which has no positive effect on machinability compared to the low-melting eutectic Bi + α-Mg3Bi2 compound, binds magnesium from the melt at an early stage. As a result, less magnesium is available for the formation of the primary hardness-increasing Mg2Si phase, which leads to a lower hardness. In order to avoid deviations in hardness, a targeted adjustment of the alloying elements, in particular magnesium and bismuth, is necessary.
These findings make an important contribution to the further development of aluminium alloys with improved machining properties that meet the requirements of modern production processes.
Translated title of the contribution | Evaluation of the strength potential of a 6xxx machining alloy |
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Original language | German |
Qualification | Dipl.-Ing. |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 20 Dec 2024 |
Publication status | Published - 2024 |
Bibliographical note
embargoed until 31-10-2029Keywords
- aluminium alloy
- strength potential
- machinability
- bismuth
- hardness