Optimization Of The Mechanical Properties And Electrical Conductivity Of Graphene Reinforced Aluminum Matrix Composites

Aluminum(Al)-based overhead power transmission lines are used to connect energy producer and consumer over long distances.They are a key component in the national power grid;therefore,their functionality and optimization are of great importance.Driving the search for new conductor materials,this Ph D thesis presents for the first time a complete study on reduced graphene oxide(RGO)-Al composites conductors,including an indepth investigation of the alumina in terms of content,size,and morphology and its impact on the mechanical behavior.These results are then complemented by room and high-temperature mechanical and electrical investigation of the wire-drawn RGO-Al composites.At first,the amount of electrical-detrimental aluminum oxide(alumina)was reduced in the newly developed,oxygen-free glovebox powder metallurgy fabrication routes.The results showed a substantial reduction in the alumina content of ～33% in the samples with a controlled processing atmosphere over the samples without.However,the processing atmosphere(air vs.argon)profoundly affected the microstructure,the size and morphology of the alumina reinforcement in the Al matrix,and subsequently the mechanical behavior of the hot rolled composites.These observations were interpreted by the alumina load-sharing through the shear-lag mechanism in samples with large alumina aspect ratios and the combined effect of the Orowan strengthening mechanism in samples with small aspect ratios.Subsequent cold wire drawing of the hot rolled RGO-Al composites(alumina content ～0.7 wt%,RGO content ～0.6 wt%)resulted in a simultaneous increase in strength and conductivity by ～8.6% and ～6.5%,respectively – a breakthrough since these properties are mutually exclusive.As a result,the composite wires exhibited a strength-conductivity combination of ～353 MPa ultimate tensile strength and ～54% international annealed copper standard,comparable or even superior to conventional Al alloy conductors that go through complex thermal-mechanical treatments.Such a property synergy was interpreted by the ultra-fine Al grain structure and the elongated grain morphology rendered by the deformation processing steps,and an Orowan-typed strengthening mechanism owing to the homogenously dispersed RGO nanosheets and natural amorphous alumina in the composite.Finally,novel micro-mechanical tests at elevated temperatures,thermal stability measurements,and state-of-the-art microstructural analysis were used to analyze the oxygen-low RGO-Al composites wires.They are shown to be stronger,stiffer,more heat resistant,and easier to fabricate than conventional high-temperature Al-based conductor materials with adequate conductivity.