Microstructure And Properties Of Graphene Nanoplatelets/Aluminum Composites Fabricated By Accumulative Roll Bonding

Aluminum matrix composites(AMCs)have become one of the most competitive engineering materials due to their excellent properties such as high strength,low density and high processability.At present,the high strength AMCs prepared in the research are usually at the expense of plasticity,and the introduction of reinforcement leads to a serious reduction in electrical conductivity of composites.It is urgently needed to prepare AMCs with high strength,high electrical conductivity and high ductility.In this study,graphene nanoplatelets reinforced aluminum matrix(GNPs/Al)composites were fabricated by a combination of accumulative roll bonding(ARB)at room temperature and hot accumulative roll bonding(HARB).The microstructure,composition,mechanical properties and electrical properties of the composites were characterized and analyzed by optical microscopy,scanning electron microscopy,X-ray diffraction,microhardness test,tensile test and eddy current conductometer.The effects of ARB cycles,HARB parameters and the content of GNPs on the microstructure,mechanical properties and electrical conductivity of composites were investigated,and the strengthening and toughening mechanisms of the composites were discussed and analyzed.The major results are summarized as follows:(1)GNPs/Al composites with different mechanical properties can be obtained by adjusting the ARB cycles,the temperature and time of HARB and the content of GNPs.With the increase of ARB cycles,the microhardness,strength and elongation of composites increased,and the electrical conductivity decreased slightly.In the case of uniform dispersion of GNPs,the increase of GNPs content is beneficial to improve the mechanical properties of composites,with only a small reduction in electrical conductivity.(2)Under the condition of 600?/30min-HARB(after 150 ARB cycles),with the increasing content of GNPs,the tensile strength of composites increased from 247MPa(0.2vol%)to 368MPa(2.0vol%),and the microhardness increased from 61.4HV to103.1HV,both of which are 2.0 times those of pure Al sample prepared by the same process;under the condition of 500?/10min-HARB,the tensile strength of GNPs/Al composites increased first and then decreased with the increase of GNPs content.The tensile strength is 261MPa to 387MPa,and the microhardness is 78.0HV to 95.1HV.The highest tensile strength can be obtained when the GNPs content is 0.5vol%,and the microhardness is 94.1HV,which are 1.6 times and 1.3 times those of pure Al sample prepared by the same process,respectively.The microhardness and strength of composites were improved significantly by the addition of GNPs,and the maximum strengthening efficiency is up to 397.The increase in strength comes from the synergy of fine grain strengthening,Orowan strengthening,CTE strengthening and load transfer.(3)GNPs/Al composites prepared in this study have good ductility.Under the condition of 600?/30min-HARB(after 150 ARB cycles),the elongation of composites with different GNPs content is 15.9%to 23.6%,which is higher than that of pure Al sample prepared by the same process(14.1%);under the condition of 500?/10min-HARB,the elongation of composites is 7.6%to 16.9%,which is also higher than that of pure Al sample prepared by the same process(13.1%)except for 2.0vol%GNPs/Al sample.When the grain size of ultrafine grained pure Al(435nm?690nm)decreases,the strength increases and the elongation decreases,however,the ultrafine grained GNPs/Al composites(263nm?757nm)exhibit different patterns of variation that the strength and elongation increase simultaneously with the decrease of grain size.The improvement of elongation is attributed to the hindering effect of GNPs bridging,pulling out and flattening on crack propagation.(4)When the cycles of ARB are 150,the microhardness of GNPs/Al composites prepared in this study is 61.4HV to 103.1HV,the tensile strength is 247MPa to 387MPa,the elongation is 7.6%to 23.6%,and the electrical conductivity is 28MS/m to 32MS/m.The 0.5vol%GNPs/Al composite prepared by 500?/10min-HARB has the best comprehensive properties:the microhardness is 94.1HV and the tensile strength is387MPa,which are 3.3 times and 4.8 times those of annealed pure Al,respectively;the elongation is 14.2%;the electrical conductivity is 30MS/m,which is 83%of annealed pure Al.The present results show that the GNPs/Al composites prepared by ARB+HARB processes can make good use of the strengthening,toughening effects and electrical conductivity of GNPs,providing an important basis for the fabrication of Al matrix composites with excellent comprehensive properties.