| As aluminum alloy has the advantages of high specific strength,low thermal expansion coefficient,good corrosion resistance and low density,it is widely used in the applications of national defense,transportation,energy,and power.However,with the rapid development of national manufacturing technology,the demand and applications of aluminum alloy pose higher requirements and more challenges.Graphene nanoplatelets(GNPs)have excellent strength,toughness,permeability resistance,corrosion resistance and self-lubricating properties,which can effectively improve the comprehensive properties of aluminum alloys,resulting in a potential improvement on mechanical properties,corrosion properties and friction properties.Therefore,graphene-reinforced aluminum matrix composites are used as the research object to expand their application range.The disadvantage of the traditional preparation method is that it is difficult to form parts with complex shapes.In this paper,selective laser melting(SLM)technology was used to prepare GNPs/AlSi10 Mg composites.The microstructure,mechanical properties,corrosion performance and friction and wear properties of GNPs/AlSi10Mg composites were investigated,and the strengthening mechanism,corrosion mechanism and friction and wear mechanism of graphene on AlSi10 Mg alloy were revealed.The main research works and results are as follows:(1)The effect of the silicon phase size and distribution on the microstructure,mechanical properties,and corrosion resistance of SLM fabricated AlSi10 Mg were studied.It was found that the hardness gradually decreases as the silicon particles grow larger.This is attributed to the weakening of solution strengthening.The increase in the distance between Si particles results in a decrease in strength.The network-like distribution of nano-eutectic silicon particles effectively improve the corrosion resistance of materials,mainly because the potential difference between the fine silicon particles and the matrix is small,and the network-like distribution of eutectic silicon benefits to producing a dense oxide film.When the silicon particles are coarsened and isolation-distributed,the corrosion resistance of materials decreases.This is mainly because the growth of silicon particles increases the corrosion driving force between the silicon particles and the matrix,which intensifies the oxidation reaction and impedes the formation of a dense protective film on the corroded surface.Besides,the local slight corrosion in the SLM fabricated AlSi10Mg alloy preferentially occurs at the boundary of the molten pool,as the remelting and growing up of eutectic silicon particles at the molten pool result in a potential difference higher than the inside of the molten pool.(2)The microstructure and mechanical properties of the SLM fabricated GNPs/AlSi10 Mg composites with different GNPs contents were investigated.Results show that the added GNPs refine the grains and increases the dislocation density of composite material but do not change the preferred growth orientation of the grains in the <100> direction.When the GNPs content is 0.1 wt.%,GNPs are evenly dispersed in the aluminum matrix and the matrix interface is well combined.The composite material is dense and has no obvious pore defects,and its strength and elongation reach 417 MPa and 8.4%,respectively,which are mainly strengthened by the mechanisms of fine-grain strengthening,load strengthening and dislocation strengthening.Besides,with the increase of GNPs content,the mechanical properties of GNPs/AlSi10 Mg composite material decrease due to the agglomeration of graphene,and the fracture morphology of the composite material is changed from plastic fracture to brittle fracture.(3)The corrosion resistance of the SLM fabricated GNPs/AlSi10 Mg composites with different GNPs contents was studied.Results show that the corrosion resistance of justfabricated samples is in a descending order of 0.1 wt.%GNPs/AlSi10 Mg,0.3 wt.%GNPs/AlSi10 Mg,0.5 wt.%GNPs/AlSi10 Mg,AlSi10 Mg.After the 50-day corrosion,the order of decreasing corrosion resistance is 0.1 wt.%GNPs/AlSi10 Mg,AlSi10 Mg,0.3 wt.%GNPs/AlSi10 Mg,0.5 wt.%GNPs/AlSi10 Mg,and the corrosion resistance of samples gradually decrease as the corrosion time increase.This is the increase of corrosion time reduces the bonding performance of GNPs and the matrix interface,resulting in a decrease in the permeability of GNPs to corrosive media.After 60-day corrosion,the GNPs “barrier” is destroyed and acts as an effective cathode,which accelerates the corrosion process of composite materials.Their corrosion resistance is in a descending order of AlSi10 Mg,0.1 wt.%GNPs/AlSi10 Mg,0.3 wt.%GNPs/AlSi10 Mg,0.5 wt.%GNPs/AlSi10 Mg.(4)The friction and wear properties of the SLM fabricated GNPs/AlSi10 Mg composites with different loads and different friction and wear speeds were studied.Results show that under the same load,the wear amount decrease with the increase of friction and wear speed,and the morphology of the wear debris changed from 2-18 ?m fine debris to 100-200 ?m flake debris.The friction and wear mechanism are changed from abrasive wear and slight oxidative wear to delamination wear and oxidation wear.This is because the large amount of frictional heat generated from high-speed wear benefits the formation of a mechanically mixed layer and reduces the damage of the worn surface.Under the same friction and wear speed,the wear amount increases with the increase of loads,and the morphology of wear debris changes from6-40 ?m fine debris to 50-210 ?m flake debris.The friction and wear mechanism are changed from abrasive wear to delamination wear and oxidative wear.This is mainly because the GNPs crack-bridging of the subsurface layer and the GNPs self-lubricating properties are beneficial to improve the tribological properties of GNPs/AlSi10Mg composite material. |
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