| The particulate reinforced aluminum matrix composites has many advantages,such as high strength,high modulus,fatigue resistance,heat resistance and wear resistance.It has been widely applied in aviation,aerospace,automobile,electronics and other high-end and engineering fields and has great potential for development.Compared with powder metallurgy,semi-solid stirring casting process is cheaper,more simple and suitable for large-scale industrial production.But there is also a disadvantage that it is difficult to disperse reinforcement particles.Therefore,mechanical vibration was introduced in this experiment to promote the dispersion of reinforcing particles.Then the hot-rolling process was adopted to eliminate the casting defects and increase the density of the composite material to prepare the B4C/Al-1.4Mg-0.8Si(wt.%)composite sheet.In this experiment,the influence of various process parameters on the microstructure and properties,the interface bonding mechanism between B4C particles and the matrix alloy and the rolling and plastic deformation mechanism of the composites were studied.The main research results include:(1)The optimum process parameters for the semi-solid stirring-vibration coupling process:stirring temperature is 640?;stirring speed is 500r/min;stirring time is 30min and vibration frequency is 100Hz.The composites prepared by this process parameters were uniformly dispersed,the porosity was low and the density was good.When 5%20?m B4C particles were added,the tensile strength of the composite was 129MPa and the elongation was 3.0%.(2)When the oxide film on the surface of B4C particles is continuous during the composite process,the bonding mechanism of B4C particles to the matrix alloy is mainly the oxide binding mechanism;When the oxide film on the surface of B4C particles is not continuous during the composite process,the grain/matrix alloy interface is mainly formed by dissolution-precipitation mechanism and the interface binding mechanism is mainly mechanical interaction,reaction binding,exchange reaction binding mechanism.Moreover,B2O3,A12O3,AlB2,Al3BC and other phases were found in the interface and the matrix.These phases can help pinning the grain boundaries and impede the movement of dislocations and improve the properties of the composite..(3)The optimal rolling parameters were determined:the rolling temperature was set at 450?,the holding time was 1h the rolling pass was 8 times,the first two passes was selected as 5%,the first two passes were selected as 5%reduction,the middle pass was selected as 15%reduction,and the last pass was selected as 25%reduction.At this point can be rolled out of dense tissue,B4C particles evenly dispersed composite sheet.After rolling,the tensile strength of 20?m 10%B4C/Al.4Mg-0.8Si(wt.%)Composite reached 183MPa,the elongation reached 7.0%,the tensile strength increased 37.6%Increased by 150%.(4)The fracture mechanism of the rolled composites is the toughness fracture of matrix alloy and the mechanism of debonding B4C particles and matrix.(5)The process of densification of the composite during rolling can be divided into the following three stages:1.In the first two passes of the composite rolling,the grains will not be deformed due to the smaller rolling reduction,but the adjacent grains will be adversely affected by the rolling force and the adjacent grain resistance The rotation occurs so that the direction of the direction of the shear stress on the sliding surface of the grain in the axial direction of the long axis of the grain is turned to the direction of the maximum shear stress;2.In the middle of the rolling of the composite material,the composite material is plastically deformed,and the grains are elongated by the external force in the rolling direction,and the number of the pores in the material is obviously reduced.3.In the last pass of composite rolling,the composite material basically reached the full density,and the severe deformation of the grains basically eliminated the residual pores in the second stage,and the grains were in close contact with the B4C grains.(6)The plastic deformation mechanism of the composite rolling process is analyzed:in the process of hot rolling,the matrix alloy undergoes plastic deformation under the action of external force,and the outer particles in the particle agglomeration area that obstruct the flow of the matrix during the deformation process are peeled off in one layer and flow with the matrix alloy.Subsequently,the matrix alloy is filled into the particle agglomeration zone,Thereby crushing the particle agglomeration area,improving the uniformity of particle distribution;at the same time,the plastic deformation of the grains during the rolling reduces the porosity defects;the distribution of B4C particles in the composite material will appear the convergence phenomenon. |
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