Influence of graphene dispersion in aluminum-graphene-composites on mechanical and electrical properties of extruded profiles

• Applicants: Professor Dr. Aleksander Gurlo; Dr.-Ing. Maik Negendank
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing ; Materials in Sintering Processes and Generative Manufacturing Processes
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426183735

• Final Report Year: 2024

Final Report Abstract

From the literature it is known that graphene can exhibit exceptional mechanical and physical properties. But that is only the case for mono-layer graphene. Van-der-Waals forces acting between graphene monolayers lead to agglomerations and thus deceasing properties of these graphene clusters. Main goal of the project was to achieve good exfoliation of graphene layers as well as a homogenous distribution of graphene in the aluminum matrix by means of different processing approaches along a powder metallurgical production route. Besides intensive mechanical mixing, processes of attritor milling, disc milling and ball milling were investigated. Composite powders containing commercial as well as self-synthesized grapheneous powders were then compacted, extruded and characterized. For the intensive mechanically mixed and the attritor milled composites little positive strengthening effect was achieved. Through short term (5min) disc milling, strengths values were increased by up to 30%. In case of tensile yield strength, the increase of 30% was achieved only for the self-synthsized ocalic acid exfoliated graphite (OAEG). With commercial GNPs strength was only increased by 20%. Results of Raman spectroscopy indicated that besides lower particle size of OAEG, OAEG consisted of fewer layers (but still multi-layer graphene) and contained less defects than commercial GNPs, which is expected to be main reasons for the better improvement of composite strengths. Ball milling processing led to the highest overall strength values of aluminum-graphene-composites observed throughout the project. By increasing ball milling speed and duration and hence higher energy input into composite powders, increases in strength of up to 212% (from UTS=114MPa to UTS=356MPa) were determined. But, pure aluminum processed the same way also increased in strength by 186% (from UTS=114MPa to UTS= 326MPa). Hence, it was concluded that the main strengthening mechanism of ball milled composites is work hardening and only about 10% was due to particle strengthening of graphene. Additional processing approaches such as shear deformation via the shear extrusion technique and a rGO-coating of aluminum powder particles via grafting did not lead to positive results. Furthermore, none of the processing approaches was able to improve the electrical conductivity of composites in comparison with pure aluminum.

Publications

• Extrusion and characterization of aluminum/graphene composites. ESAFORM 2021.
  Negendank, Maik; Faezi, Hamidreza Rabi; Ovsianytskyi, Oleksandr; Goerke, Oliver; Gurlo, Aleksander & Müller, Sören
  
• Aluminum-Anodes for Metal-Air-Batteries. The Minerals, Metals & Materials Series, 467-477. Springer Nature Switzerland.
  Heydrich-Bodensieck, Janne Max; Negendank, Maik & Müller, Sören
  
• Effects of disc milling and indirect extrusion processing on mechanical properties of aluminum-graphene-composites with commercial GNPs. Materials Research Proceedings, 28, 455-466. Materials Research Forum LLC.
  NEGENDANK, M.
  
• Effect of ball milling processing on mechanical properties of extruded aluminum-graphene-composites with commercial and self-synthesized graphene sources. Materials Research Proceedings, 41, 696-705. Materials Research Forum LLC.
  NEGENDANK, Maik