Research Of Fabrication Of 2D-C_f/Al Composite And Its Part By Liquid-solid Extrusion Following Vacuum Infiltration Technique

Liquid-solid extrusion following vacuum infiltration technique(LSEVI)is a new method to fabricate composites under vacuum.Its essence is to make the matrix alloy infiltrate into the fiber preform uniformly in the high temperature liquid phase state,and then alloy is formed under high temperature and high pressure and is forced to fill.Finally,the composite materials with the ideal microstructure and properties are obtained.Carbon fiber reinforced aluminum matrix(C_f/Al)composite has the characteristics of low density,high specific strength and stiffness and low coefficient of thermal expansion,which is the research focus of lightweight and high performance materials.However,the wettability of carbon fiber and aluminum alloy is very poor and they are easy to get oxidized at high temperature.2D carbon fiber preform has high fiber volume fraction,and fiber gaps are small and uneven,which has large critical infiltration pressure.It is very difficult to achieve fully uniform infiltration,which is a great challenge to prepare satisfactory 2D-C_f/Al composite materials.In the preparation of 2D-C_f/Al composite parts,it is important to overcome the difficulties in the preparation of composites.Moreover,ensuring the good shape and quality is also very necessary,and the effective preparation of the composite parts has become an important challenge.Only by solving these problems,this kind of composite materials could be applied.LSEVI could solve the preparation problems above,and it could provide high vacuum level,large infiltration pressure and so on.Composite part is capable of being implemented in effective preparation by it.There are many problems such as obvious interaction and bad wettability between carbon fibers and aluminium alloy,complex process parameters,many defects,and having large difficulties to prepare composites in the preparation process of 2D-C_f/Al composite.In this paper,deep research of LSEVI is carried out,and effective fabrication of 2D-C_f/Al composite by LSEVI is as the research object.2D-C_f/Al composite with sufficient and uniform infiltration effect,few defects,high performance,and satisfied composite part is the ultimate goal of the research.The main research contents are as follows.(1)The overall scheme of fabricating 2D-C_f/Al composite by LSEVI was proposed.According to in-depth analysis of LSEVI process and different study solutions of mould heating furnace,silicon carbide heating furnace was determined to be the best scheme,and it was designed and processed.Aluminium alloy smelting crucible was improved,and bilayer structure device of graphite and metal for the aluminum alloy smelting was designed and developed.Aluminum alloy vacuum casting system and forming die were designed and processed,and process experiment system of LSEVI to fabricate 2D-C_f/Al composite was finished ultimately.(2)From the static,the analysis and calculation of critical infiltration pressure were finished of aluminum alloy in the two-dimensional layer carbon fiber preform.Critical infiltration pressures under different fiber volume fractions from 10% to 50% were calculated,and the results showed that critical infiltration pressure increased with the increasing of the fiber volume fraction of the carbon fiber preform.From the dynamics,the analysis and calculation of variation between infiltration time and infiltration height were done under different infiltration pressures from 0.1MPa to 0.9MPa.The results showed that infiltration height increased with the increasing of infiltration time under the same infiltration pressure.Meanwhile,infiltration height increased with the increasing of infiltration pressure if the infiltration times were the same.The critical infiltration pressure of 2D carbon fiber preform in this study is 3.24 MPa,which is slightly lower than the actual test of 6~7MPa.The influence of process parameters on the preparation of 2D-C_f/Al composite was studied by the design of the pressure infiltration device and LSEVI test system.The experimental results are consistent with the former theoretical research,which lays the foundation for the following research of preparation 2D-C_f/Al composite with ideal microstructure and mechanical properties.(3)The influence of process parameters on 2D-C_f/Al composite was studied deeply.Main defects were studied in LSEVI,which included preform deformation,micro holes,unsatisfied infiltration and fiber damage,unreasonable tensile fracture and internal cracks.All of them were very bad for preparation of high-performance 2D-C_f/Al composites,and unreasonable process parameters were the main reasons to appear.The effects of four factors of LSEVI on the mechanical properties of the composites could be expressed as follows.(Squeeze pressure)>(Preheating temperature)>(Squeeze temperature)>(Melting temperature).The squeeze pressure was the most significant factor to fabricate the high performance C_f/Al composites.By using the method of orthogonal experimental design,optimized process parameters of LSEVI were obtained as follows: the squeeze pressure was 70 MPa,preheating temperature was 615 oC,squeeze temperature was 620 oC,melting temperature was 780 oC,and vacuum degree is 0.09 MPa,under which the ideal 2D-C_f/Al composite part could be prepared.UTS of 2D-T300/Al composite prepared using LSEVI reached 263 MPa,and it was improved by 120% than that of matrix.On the basis of above-mentioned analysis,useful methods and measures were obtained,which were able to reduce the defects in the process of the LSEVI technique.(4)The effect of different fiber layer orientation angles on the 2D-C_f/Al composites was explored,and the effect of the changed angles on the microstructure and properties of the composites was revealed.Through the method of fiber lamination,carbon fiber preforms with different orientation angles of 30o,45o,60oand 90o were prepared,and 2D-C_f/Al composites were fabricated by LSEVI.It was found the volume fraction of four kinds of preform was about 45%.In the microstructure of composites,there were lots of carbon fibers with elliptical shapes in the upper carbon fiber bundle,and their size was gradually increased.This was because there were fiber orientation angles between adjacent fiber layers,and this could be showed in the cross sections.Through mechanical properties test of composites above,it showed that ultimate tensile strength(UTS)of the obtained C_f/Al composite was improved greatly than that of matrix alloy.When the angle was 90o,and fiber bundles were orthogonal between adjacent fiber layers.When the angles were 45° and 90°,the increased rates were 112.5% and 63.9%,respectively.Fiber bearing capacity of four kinds of composites was calculated through theoretical method.When fiber orientation angles of 2D-C_f/Al composite were different,fiber bearing capacity Fn of nth layer could be calculated by formula Fn=|F×cos[(n-1)×?]|,(0o???90o).When the fiber orientation angles were 30o,45o,60o and 90o,respectively,increased rates of composites UTS were to increase initially and then to decrease.Through theoretical calculation and analysis,the experimental results and theoretical calculation matched well with each other.Through theoretical calculation and experiments,it was found that total fiber bearing capacity in the tension direction was one of the significant factors to UTS of composites.(5)The effective preparation of the 2D-C_f/Al composite special shaped-part by LSEVI was studied,and the experience of satisfied forming technology of 2D-C_f/Al composite part was obtained.By comparing the three kinds of composite preparation schemes of whole forming and processing type,semi modular splicing type and graphite cavity forming,it was found that the third scheme was the best one,which has a simple operation process and low cost.Combining with the composite profile,graphite mould was manufactured to achieve effective forming of composite special shaped part,and 2D T300 carbon fiber preform were prepared by fiber layer method.2D-C_f/Al composite special-shaped part without the obvious macroscopic defects were prepared by LSEVI.(6)The analysis and testing of the 2D-C_f/Al composite special shaped-part by LSEVI was carried out.Infiltration of 2D-C_f/Al composite special-shaped part was full and uniform,and the casting defects could not be found.Its density was 2.23g/cm3,which was lower at 17.9% than that of matrix,and the porosity was 1.4%.Test results showed that CTE(Coefficient of thermal expansion)of composite was less than that of matrix alloy below 300?.CTE of matrix alloy increased with increasing temperature.CTE of composites increased with the increase of temperature in longitudinal direction of composites,too.However,it decreased in transverse direction.At low temperature of 100?,CTE of this kind of composite was equivalent to only 52.2% and 22.5% of matrix alloy respectively in transverse and longitudinal direction.At high temperature of 300?,it was even equivalent to only 28.7% and 51.4% in transverse and longitudinal direction.UTS of composite part had been increased by 115.8% than that of matrix,and tensile fracture was satisfied.This showed 2D-C_f/Al composite special-shaped part could be prepared by LSEVI,and this will provide a good reference for the reliable and stable preparation of 2D-C_f/Al composite materials and its application in industrial application.