Preparation And High Temperature Mechanical Properties Of Graphene Reinforced Aluminum Matrix Composites

Aluminum matrix composite has the advantages of high specific strength and high specific modulus,and has been widely used in aerospace,shipping,transportation and other industrial fields.However,the low mechanical properties of aluminum matrix composites limit their application in the field of high temperature,so it is necessary to improve the high temperature properties of the materials.At the same time,graphene has been paid close attention by many scholars because of its excellent properties.Therefore,in this paper,Graphene(Gr)is used as the reinforcing phase,and 6061-T6 aluminum alloy is used as the substrate.The graphene reinforced aluminum base(Gr/6061Al)was successfully prepared by Rotating Friction Extrusion(RFE)Composite materials.This paper studied the effects of process parameters and graphene content on the forming of the composite,established the heat treatment process specification of the composite,and discussed the changes of the structure of the composite before and after heat treatment.Finally,analyzed the effects of RFE and heat treatment on the high temperature mechanical properties of Gr/6061Al composite.The results show that:Gr/6061Al composites with good forming and uniform microstructure were successfully prepared by RFE method.Too high or too low extrusion speed and rotation speed will affect the surface forming of materials.When graphene is less than 1.5vol.%,the composite has a good shape,but with the increase of graphene,the shape of composite is getting worse and worse;The structure of RFE matrix is fine equiaxed crystal,and the grain size of the composite becomes finer when graphene is added;With the increase of graphene content,the microhardness of the composite increases first and then decreases;The formation of Al₄C₃ phase in composite materials can be effectively avoided by RFE,but the number of second phase in matrix decreases and coarsening occurs;The interface between the Mg₂Si phase and the?-Al phase in the substrate is a coherent interface.After RFE,the Mg₂Si phase and the?-Al phase in the composite material become a semi-coherent interface.The best heat treatment parameters of the composite material are solid solution temperature of 540?+4h,and aging temperature of 175?+12h;After heat treatment,the grain size of Gr/6061Al composite is further reduced,the structure is more uniform,and the hardness of the composite is greatly increased;The brittle phase Al₄C₃ was not generated in the composite after heat treatment,and the size of the second phase decreased and the number increased significantly,the interface between the reprecipitated Mg₂Si phase and the?-Al phase was coherent interface.The tensile strength,yield strength and elastic modulus of Gr/6061Al composite prepared by RFE method increased first and then decreased with the increase of graphene;When the graphene content is 1.5vol.%,The tensile strength,yield strength,and elastic modulus of the composite material reach the maximum;The fracture of the composite material obviously exhibits good ductile fracture characteristics,but with the increase of graphene,the elongation of the composite material has been reduced,and the plasticity has deteriorated.Before heat treatment,the tensile strength and yield strength of the composite increased first and then decreased with the increase of temperature,while the elongation was opposite,the modulus of elasticity decreased with the increase of temperature;At300?,the tensile strength of 1.5vol.%Gr/6061Al composite is 70.1MPa,which is 60.0%higher than that of RFE;The fracture of the composite material is ductile fracture at high temperature.As the temperature increases,the dimples of the composite material become larger and deeper,and the plasticity is getting better and better.Heat treatment can greatly improve the high temperature strength of Gr/6061Al composites,but makes the plastics of the composites worse;After heat treatment,the tensile strength,yield strength,elongation and elastic modulus of the composite decreased with the increase of temperature,however,at the same temperature,the strength of the composite is higher than that of the substrate and the RFE-T6 substrate;At 300?,the tensile strength of 1.5vol.%Gr/6061Al-T6 composite is 139.0MPa,which is an increase of 98.3%compared with that before unheat treatment;In addition,with increasing temperature,the fracture mode of Gr/6061Al-T6 composites gradually changed from ductile fracture to ductile-brittle mixed fracture.The Gr/6061Al composite prepared by RFE is a mixture of four strengthening mechanisms:dislocation strengthening,fine grain strengthening,second phase strengthening and load transfer strengthening,which is not simply a direct addition.