Study On The Rheological And Frictional Properties Of Nano-SiC_p Reinforced Aluminum Matrix Composites

Particles reinforced aluminum matrix composites?PAMCs?,with a wide application prospect,have many nice properties,for instance,high specific stiffness,high specific strength,high wear resistance,good thermal stability and so on.The addition of Nano-sized SiC particles can improve hardness,wear resistance.Simultaneously,the composites can avoid the reduction of ductility or tensile strength,which?m-sized particles cannot overcome.Therefore,the application potential and value of Nano-SiC_p/AMCs?NPAMCs?are very great.However,the occurrence of agglomeration and clusters of Nano-SiC_p and in the melt is detrimental to composites properties,due to the high specific area of Nano-SiC_p and the poor wettability between Nano-SiC_p and aluminum-alloy slurry.In order to solve this problem and develop new composites,our laboratory has developed an innovational fabricating and forming process,which offers Nano-SiC_p/AMCs with uniform dispersion of SiC_p,good mechanical properties and high wear resistance.Considering that the researches on Nano-particle reinforced AMCs are still at the stage of preparation process and primary optimization of microstructure and properties so far,there are few studies on its rheological properties,fluidity and friction and wear properties.Therefore,this paper has firstly studied the ultrasonic process of Nano-SiC_p/AMCs with different content and their microstructure and mechanical properties,then the rheological properties,fluidity and friction and wears properties of Nano-SiC_p/AMCs with different content of SiC_p were also researched,and this paper revealed the influence law of changing SiC_p content on the above properties of the composites.The preparation of SiC_p/Al-5Cu composites with different nano-SiC_p contents was investigated.The agglomeration and clusters of SiC_p was effectively broke up and the grains were refined by ultrasonic vibration with the effects of acoustic cavitation and acoustic streaming.When the ultrasonic time was 3min,the distribution of SiC_p was significantly improved,and the primary?-Al grain and Al₂Cu phase were also obviously refined.As SiC_p content increased,the morphology of primary?-Al grains transforms from coarse dendrites to rose-shaped crystals or nearly spherical grains,and the size of?-Al grains decreased gradually.When the mass fraction of SiC_p reached 1.5wt%,the primary?-Al grain refinement effect was the best,which is 57%smaller than the average particle size of the matrix alloy.In addition,the tensile strength,yield strength and elongation of the composites are 289MPa,169MPa and 12.9%,which are 15.1%,12.7%and 24.0%higher than the matrix alloy respectively.When SiC_p content reached 2wt%,the effect of ultrasonic vibration was affected due to the high viscosity,which carried some spontaneous agglomeration of SiC_p and grain size increased as grain refinement decreased.The effects of Nano-SiC_p content on the apparent viscosity,rheological behavior and fluidity of SiC_p/Al-5Cu and SiC_p/A356 composites were studied,and the relevant model for forecasting were established then.The apparent viscosity and fluidity of the composites were measured by coaxial rotating cylinder method and spiral method respectively.With the increase of SiC_p content or the decrease of temperature,the apparent viscosity of composites slurry will rise rapidly while the fluidity will decrease gradually,which mainly due to the greatly enhancement of viscous force of the melt with the addition of Nano-SiC_p.The effects of SiC_p on the apparent viscosity of semisolid composites decreased rapidly with the increase of solid fraction.A356 Al-Si matrix alloy has lower viscosity and better fluidity than Al-5Cu matrix alloy under the same conditions.With the content of SiC_p increased,the effect of SiC_p on the degree of increase of apparent viscosity of Al-5Cu composites was gradually larger than that of A356,and so the degree of decrease of fluidity was.It should be noted that the slurry would stop flowing soon when high mass fractions of the SiC_p were added because of the poor fluidity of it now even at very high temperatures.There were a large number of hard solid particles in the slurry,leading to a high level of solid phase rate.The thixotropic properties of the two composites were measured at a constant shear rate.At the beginning,the thixotropic properties of the two composites were characterized by shear thinning.However,when the slurry was stabilized after being stirred and rotated for some time,the matrix alloy would decrease slightly while the apparent viscosity value of the composites would gradually increase,which was mostly due to the spontaneous agglomeration of SiC_p and the formation of slag of the melt.The models of the effects of Nano-SiC_p content on the apparent viscosity(?_AMC)and liquidity(L_AMC)of Al-5Cu composites were established under the 700?:?_AMC=?_A?0.23338?²₄)+0.718888m_SiC)+0.94905),L_AMC=L_A(1.001-0.0568m_SiC)-0.0648)m_SiC²))?0.5?m?2?,respectively.It is revealed that the effects of SiC_p content on the apparent viscosity and fluidity of composites is opposite,but the relationships between the content of SiC_p and the apparent viscosity or fluidity of composites are both quadratic.The relationship between the Nano-SiC_p content and the hardness and tribological and wear properties of SiC_p/Al-5Cu composites was studied.With the increase of SiC_p content,the hardness of composites enhanced,and it reached the highest when the content reached2wt%,which is 34.36%higher than that of matrix.The friction and wear mechanism of Al-5Cu matrix alloy is principally abrasive wear and peeling wear,while Al-5Cu composites reinforced by SiC_p are primarily abrasive particles wear and partial adhesive wear.As the content of SiC_p increased,the proportion of adhesive wear gradually rose with more pits,the surface furrows of the composites become shallow and the feature of grinding cracks gradually reduced.Besides the amount and size of adhesive abrasive dust become more and smaller respectively,and the roughness of surface increases compared with the matrix alloy.The composites are mainly abrasive particles wear and partial adhesive wear under low load.There are a lot of rough friction surfaces and pits crossed the relatively clear furrows and friction scratches.The composites under high load are mainly adhesive wear with some abrasive particles wear.There is a large number of rough friction surfaces and pits which become larger.The characteristics of furrows and friction scratches basically disappeared.