Study On Aging Behavior Of GNPs/Al-Mg-Si Composites

In this paper,different kinds of GNPs/Al-Mg-Si composites were prepared by pressure infiltration method.The aging behavior of GNPs/Al-Mg-Si composites was systematically studied by using Brinell hardness tester,differential scanning calorimetry,scanning electron microscope(SEM),transmission electron microscopy(TEM)and electronic universal testing machine.The effects of graphene nanoplatelets(GNPs)on the Mg,Si diffusion and interfacial segregation behavior of alloying elements were studied.The effect of Mg and Si content on the aging microstructure and mechanical properties of the composites was investigated.The DSC and age hardening results of the composites show that,the addition of GNPs causes the exothermic peak of the aging phase to move to the high temperature region,and the exothermic enthalpy decreases.The age hardening rate of the composite is much lower than that of the matrix alloy.By adding Mg element,the number of aging precipitation phases of the composite material can be increased,and the exothermic peak of the ??? phase is more obvious,and the age hardening rate is gradually increased.When the Mg content is 2.18 wt.%,the age hardening rate is comparable to 6061 Al.After increasing the Si element content,the Mg/Si ratio in the matrix decreases,the exothermic peak of the DSC curve is passivated,and the age hardening rate decreases.By observing the microstructure of the composite,the addition of GNPs did not change the aging precipitation order of the composite,but the number and size of the precipitates in the composite changed.This is due to the fact that the Mg element is segregated at the interface,and there is not enough Mg element in the matrix to participate in the aging precipitation.By increasing the content of Mg element,the segregation and consumption of Mg elements by GNPs can be effectively compensated,and the number and size of aging precipitates are increased.However,further increasing the Si content reduces the Mg/Si ratio in the matrix of the composite,resulting in a decrease in the number and size of the aged precipitates.The structure of GNPs-Al interface was observed.It was found that the structure of GNPs was complete and the matrix was well bonded.A small amount of Al4C3 was formed near the interface,and the Mg element was segregated at the interface and existed as an oxide.Tensile tests on composites(peak ageing)show that GNPs reduce the ageing strengthening of composites compared with matrix alloys.With the increase of Mg content,the tensile strength of composites is improved,indicating that Mg The addition of elements achieved synergistic strengthening of GNPs and artificial aging in the composite.When 2.18 wt.%Mg was added,the yield strength of the composite reached 330.96 MPa and the elastic modulus was 88.97 GPa.However,with the increase of Si content,the tensile strength and elongation of the composite are both reduced.The fracture of the composite material has obvious dimples and tear ing ribs,showing microscopic ductile fracture.The strengthening mechanism of GNPs/AlMg-Si composites is mainly load transfer mechanism,dislocation strengthening mechanism and precipitation strengthening mechanism.