Study On The Mixing Process Of Graphene And ZK61 Magnesium Alloy Powder

To overcome the agglomeration of graphene itself,the dispersion problems of graphene within magnesium alloy and the difficulty in fabricating magnesium matrix composite,a novel technique for preparing and forming graphene reinforced magnesium based composite—ultrasonication powder thixoforming was proposed in this work by combining the merits of ultrasonic treatment,powder metallurgy and thixoforming technologies.Therefore,the ultrasonic treatment process of graphene nanosheet(GNPs)was first studied,and subsequently,the pickling process of ZK61 powder and the mixing process of ZK61 powder with GNPs or Go was investigated respectively.Finally,we tried to prepare GNPs/ZK61 Mg based composite and Go/ZK61 Mg based composite by utilizing ultrasonication powder thixoforming method.The obtained results indicated that:In ethanol solvent,ultrasonic treatment had a significant dispersing effect on GNPs.The dispersing process can be divided into three stages: First one was the dispersing of agglomerates,second one was the fragmentation and exfoliation of GNPs,and last one was the further size decrease of the GNPs due to the fragmentation effect,and GNPs tended to be uniform.GNPs are preferentially broken from their own defects,resulting in the improvement of the order of GNPs structure.Then vacancy defects occurred,leading to the damage in the structural integrity of GNPs.Prolonging ultrasonic time can improve the dispersing effect of GNPs,and will generate vacancy defects if the time was too long;Increasing the ultrasonic power will improve the dispersion efficiency of GNPs,but its fragmentation was quite severe and the number of generated vacancy defects was large at the same time.Lower solvent temperature led to the more uniform dispersion of GNPs;Low viscosity and high surface tension can improve the cavitation strength,which can improve the dispersion effect.When the amplitude transformer extended into the liquid surface at a relatively smaller distance,the concentration of GNPs was relatively lower and the diameter of container was comparatively smaller,the dispersion effect of GNPs was better.The optimum process parameters obtained in this work were as folloes: the suspension liquid concentration was 1.5 mg/ml,ethanol solvent temperature was 25°C,the distance of amplitude transformer inserted the liquid was 15 mm,the glass vessel was 65 mm in diameter,the ultrasonic power was 960 W,ultrasonic processing was 4 h.Under the aforementioned parameters,the GNPs can be dispersed uniformly with a relatively less structural damage.Excessive process parameters seriously damaged the structure of GNPs,and otherwise,a poor dispersion effect can be achieved.Go suspension was prepared by ultrasonic treatment at 840 W in ethanol solvent containing 10 vol.% distilled water for 40 min.In order to get the GNPs and ZK61 powder uniformly mixed,the ZK61 powder was treated with acid pickling to remove the oxide at first.a adhesion process was used to prepare the GNPs+ZK61 mixed powder,and the type of adhesive,amount of adhesive and GNPs amount on the gluing effect of GNPs+ZK61 were studied.The results disclosed that when 0.3wt.% Hexadecyl trimethyl ammonium Bromide was used as adhesive to adhere 0.2 wt.% GNPs and ZK61 powders in ethanol solution,each powder uniformly adhere GNPs,and GNPs was not agglomerated.Subsequently,an electrostatic attraction process was employed to prepare the Go+ZK61 mixed powder,Firstly,the effects of ultrasonic stirring time,mechanical stirring speed and strong or weak acid on the powder uniformity of pickling ZK61 were studied.Then the effects of the concentration of glacial acetic acid,the amount of Go,the amount of distilled water and the liquid filtration method on the electrostatic attraction effect of Go+ZK61 were investigated.The results indicated that when the ZK61 powder was pickling with ethanol solution containing 1 vol.% glacial acetic acid,and was mixed with ultrasonic stirring for 4 min at a speed of 160 r/min,the ZK61 powder with oxide removal and positive charge can be obtained.After being mixed with 0.1 wt.%Go suspension,static precipitation and vacuum drying was conducted to obtain the mixed powder,the absorption of Go on the surface of ZK61 powder was realized.The GNPs+ZK61 mixed powder and Go+ZK61 mixed powder obtained under the above optimum parameters as well as the ZK61 matrix powder was first hot-pressed at 300? and 282 MPa,and then the green billets was heated at 630? for 60 min to obtain a semisolid ingots,which was finally moved to mold with temperature of 300? and thixoforged under a pressure of 330 MPa.The results indicated that the ultimate tensile strength(UTS),elongation and Vickers hardness of ZK61 base alloy were 164.33 MPa,5.62% and 60.08 HV,respectively.The UTS,elongation and vickers hardness of 0.2 wt.%GNPs/ZK61 Mg matrix composites were 211.6 MPa,5.5% and 59.0HV,respectively.The UTS,elongation and vickers hardness of 0.5wt.%GNPs/ZK61 Mg matrix composites were 176.61 MPa,5.63% and 61.27 HV.The UTS,elongation and vickers hardness of 0.1 wt.%Go/ZK61 Mg matrix composites were 234.9 MPa,6.0% and 64.0 HV,respectively.The UTS,elongation and vickers hardness of 0.5wt.%Go/ZK61 Mg matrix composite were 97.64 MPa,3.68% and 55.98 HV,respectively.That is,composite materials with proper amount of reinforcement had a significant higher UTS than the base alloy,but the elongation did not decrease and the hardness remained nearly unchanged.The mechanical properties of Go/ZK61 Mg based composites with excessive Go addition were significantly decreased compared with that of the ZK61 base alloy.