Effect Of ECAP And Heat Treatment On The Microstructure And Properties Of GNPs Reinforced Aluminum Matrix Composites

In this paper,the effects of graphene（GNPs）reinforced aluminum alloys were investigated.The heat treatable alloy ADC12 was selected to investigate the heat treatment on the microstructure,mechanical properties and dry sliding friction wear properties of ADC12-GNPs composites.Deformable aluminum alloy 2014 was selected to investigate the effect of isometric angle extrusion on the microstructure and mechanical properties of 2014-GNPs composites.Effects of T6 heat treatment on the microstructure and mechanical properties of graphenes（GNPs）reinforced ADC12 alloy were investigated.The results showed that the average size of Si phase was decreased from 57.2μm to 16.3μm after T6 heat treatment.The precipitates Al₂Cu nucleate preferentially at GNPs/Al interface owing to dislocation provide an effective diffusion channel for Cu elements.Moreover,uniformly distributed Al₂Cu could be observed at grain boundaries because active solute atoms spontaneously reduced energy and transferred to the grain boundaries.Comparing with ADC12-0.9wt.%GNPs composites,ultimate tensile strength（319.6MPa）,yield strength（245.8MPa）,elongation（3.26%）and hardness（180.6HV）of ADC12-0.9wt.%GNPs composites/T6 composites increased 37.58%,36.40%,26.36%and 49.88%,respectively.Due to GNPs addition,the ADC12-0.9wt.%GNPs composites reached peak ageing earlier 2h than ADC12 alloy.Meanwhile,GNPs produced load transfer strengthening,dislocation strengthening,and Orowan strengthening in concert with ageing strengthening,which together promoted the improvement of mechanical properties.In addition,frictional wear tests were conducted by subjecting ADC12,ADC12-0.9 wt%GNPs composite and ADC12-0.9 wt%.GNPs composite after T6 to the same load and further investigating the effect of different loads on the wear resistance of ADC12-0.9wt%GNPs composite after T6.SEM morphology analysis and EDS analysis of the material revealed that the wear rate of the ADC12 was 29.8×10^-3mm³/m at a load of 40N,which was 41.94%less than the wear rate of 17.3×10^-3mm³/m for the ADC12-0.9wt.%GNPs composite.Because graphene acts as a lubricant in the composite,it increases the wear resistance and reduces the wear rate of the composite.During the experiments,ADC12-0.9wt.%GNPs composite after T6gradually changed from exfoliation wear to abrasive wear,and then from abrasive wear to exfoliation wear as the applied load increased.As the load increases,the area of carbon film formation increases and the friction coefficient gradually decreases.As the load keeps increasing,the average diameter size of the abrasive chips increases,some of the graphene on the surface of the friction pin is ground or pulled out,and the friction heat promotes the formation of carbon film.The 2014-GNPs composites were subjected to single-pass equal-circle angle（ECAP）extrusion treatment.Under the single-pass ECAP process conditions,the microstructure of the composites and the dispersion of graphene showed a trend of first getting better and then worse with the increase of graphene content,and the average grain size was 28.4μm when the graphene addition was 0.8%.The extrusion temperature of the 2014-0.8wt.%GNPs composites was explored under single-pass ECAP process conditions,and with the increase in temperature,the microstructure of the composites had an average grain size of 20.7μm at 300°C.At this time,the tensile strength was 497.3MPa,yield strength was 406.2MPa,elongation was 8.7%,and hardness was 348.7HV,which are62.30%,52.08%,67.31%and 77.64%higher than the 2014 composites,respectively.Under single-pass ECAP process conditions,the tensile fracture of 2014 was brittle fracture and 2014-0.8wt.%GNPs composites were ductile fracture,however,the toughness nests were larger.2014-0.8wt.%GNPs composites after ECPA deformation had fine toughness nests and were ductile fracture.