Research On Preparation Of SiCp Porous Preforms And Vacuum Pressure Infiltration Of Liquid Aluminum Alloys

As a near-net shape forming technology for producing SiCp/Al composites with high volume fraction,the liquid infiltration method has recently drawn attention by numerous researchers.The preparation of SiCp porous preforms and parameters during the infiltration process has significant effect on the microstructure and properties of SiCp/Al composites.In this study,a vacuum pressure liquid infiltration experimental apparatus was designed and manufacted,which has been applied to the SiCp/Al composites preparation,and effects of several processing parameters on the microstructure and properties of SiCp/Al composites,were investigated.Considering the limitation of current liquid infiltration experimental apparatus for forming SiCp/Al composites and to obtain the intermediate status of liquid aluminum infiltration,the basic parameters of the vacuum pressure liquid infiltration experimental apparatus were designed,The maximum value of pressure and temperature for the apparatus are 3.0MPa and 1200?,respectively.Then the experimental apparatus and its accessories were designed and manufactured.The infiltration experiments with aluminum dihydrogen phosphates as binder were carried out.The un-successful infiltration was analyzed.Hence the preparation process of SiCp porous preforms was optimized.The SiCp porous preforms with a good appearance were prepared by using ?-SiC particles,Ammonium bicarbonate?pore-forming agent?and Ludox?binder?as raw materials during the mould-forming and sinter processing.The SiCp porous preforms were successfully infiltrated by liquid aluminum alloys with the liquid infiltration experimental apparatus by using a higher vacuum.The microstructure of the prepared SiCp/Al composites has shown that the SiC particles with a sharp outline and few pores were found,and the brittle phase?Al₄C₃?was hardly to be found in the interface between the particles and the matrix.The SiCp/Al composites with different particles size of ammonium bicarbonate?150?m,200?m,250?m and 300?m?,contents of magnesium?0wt.%,5wt.% and 8wt.%?and infiltration pressure were prepared by the vacuum pressure infiltration process.The microstructure,porosity,bending strength and fracture morphologies of composites under different process parameters were analyzed.The effects of the particle size of ammonium bicarbonate,the Mg element content and infiltration pressure on the microstructure and properties of SiCp/Al composites were discussed.When enlarging the size of ammonium bicarbonate,the spaces among SiC particles will decrease,which not only makes the infiltration of liquid aluminum into the space more difficult,but also increases the porosity contents and decreases the bending strength of composites.Besides,as the increase of magnesium content,the liquid aluminum will have a better infiltration ability due to improved wettability,and the composites with lower porosity and higher bending strength were obtained.It is to be noted that the composite porosity content raised slightly and the bending strength declined when the content of magnesium further increase to 8wt.%.With the increase of infiltration pressure,the infiltrability of liquid aluminum into small pores was improved.As a result,the obtained composites were with lower porosity and higher bending strength.