| ZL205A alloy is a typical high-strength cast aluminum-copper alloy,have high strength and excellent plastic toughness,high temperature performance and cutting operation performanc,attracts the attention of researchers.Using aluminum instead of steel is an important means to realize automobile lightweight,which can greatly reduce the quality of automobile parts,save energy,reduce cost.In order to meet the higher demand of automobile lightweight for strength and plasticity,nano phase reinforced aluminum matrix composites were designed with high strength and plasticity ZL205A alloy as the matrix to further improve the strength and plasticity.In the traditional alloying route,it is difficult to take both strength and plasticity into account.In this paper,the ZL205A alloy as the matrix,and the two-dimensional nanostructured graphene is used as the reinforcement.Graphene/ZL205A aluminum matrix composites are prepared by the stirring casting method.Using metallographic microscope,scanning electron microscope,transmission electron microscope,systematically studied the influence of graphene addition and different heat treatment processes on the microstructure of composite materials.The hardness,tensile properties and corrosion resistance of graphene/ZL205A aluminum matrix composites were tested,and the effects of graphene addition and different heat treatment processes on the properties of composites were studied.Explains the strengthening mechanism and fracture mechanism of the composite material,and explores the mechanism of the heat treatment process on the microstructure and mechanical properties of the composite material,and optimizes the best heat treatment process.The main research conclusions are as follows:The as-cast structure of ZL205A aluminum alloy is composed of a typicalα-Al phase and Al2Cu eutectic phase,and the coarse Al2Cu eutectic phase presents a continuous distribution at the grain boundary.Compared with the ZL205A alloy,the addition of graphene significantly refines the primaryα-Al phase and Al2Cu eutectic phase in the graphene/ZL205A composite.When the amount of graphene is 0.3wt.%,the average grain size ofα-Al decreases from 80μm to 25μm,the size of the Al2Cu eutectic phase at the grain boundary becomes smaller,and the partially separated Al2Cu eutectic phase becomes elongated transform into a spherical shape.The addition of graphene has little effect on the grain size of the ZL205A alloy（T5 state）,resulting in a significant change in the grain boundary Al2Cu eutectic phase size and morphology.Compared with the ZL205A alloy,the Al2Cu eutectic phase in the 0.3wt.%graphene/ZL205A composite is basically completely spheroidized and dispersed finely on the grain boundaries.Compared with ZL205A aluminum alloy,when the graphene content increases from0wt.%to 0.5wt.%,the tensile strength,yield strength and elongation of the graphene/ZL205A composite material are significantly improved,0.3wt.%graphene/ZL205A composite material has the best mechanical properties.Compared with ZL205A aluminum alloy,the tensile strength,yield strength and elongation of 0.3wt.%graphene/ZL205A composite are 475MPa,417MPa and 6.0%respectively,which increased by 10.4%,5.8%and 33.3%,respectively.The increase in composite strength is mainly attributed to the grain refinement strengthening and graphene load-bearing strengthening,and the increase in elongation is mainly due to the refinement ofα-Al grains and Al2Cu eutectic phase.Compared with the ZL205A alloy,the fracture mode of the 0.3wt.%graphene/ZL205A composite material gradually changed from the brittle fracture of the base alloy to the ductile intergranular fracture.The effects of solution temperature（525℃,530℃,535℃,540℃）and solution time（535℃/10h,12h,14h,16h）on the microstructure and mechanical properties of 0.3wt.%graphene/ZL205A composites were studied by the control variable method.The results show that the best solution treatment process for 0.3wt.%Gr/ZL205A aluminum matrix composites is 535℃/14h,the Al2Cu eutectic phase is basically dissolved,and theα-Al grains have not grown significantly.Based on the single-stage aging process,three pre-aging temperatures（100℃,110℃,120℃）are selected,and the best two-stage aging treatment process of0.3wt.%Gr/ZL205A is 120℃/4h+152℃/6h,the tensile strength reaches 480.2MPa,the yield strength reaches 431.0MPa,and the elongation rate is 6.5%.This may be due to the fact that graphene can be used as the nucleation core of the GP zone during the pre-aging process,and theθ"phase in the final aging process takes the GP zone generated during the pre-aging process as the basal nucleation.The greater the number of GP zones,the shorter the time required for the composite to reach peak aging.Compared with ZL205A aluminum alloy,when the graphene content increases from0wt.%to 0.5wt.%,the self-corrosion potential of the composite material gradually shifts to the right.Compared with ZL205A aluminum alloy,the effect of graphene addition on the pitting potential is not obvious.Compared with 152℃/8h single-stage aging treatment,0.3wt.%graphene/ZL205A aluminum matrix composites have better corrosion resistance after 120℃/4h+152℃/6h double-stage aging treatment.The self-corrosion potential is reduced by-1.281V rose to-1.127V.This is mainly due to the dispersed Al2Cu phase and narrow PFZ on the grain boundary,which reduces the tendency of microbattery corrosion at the grain boundary. |
