Research On Preparation Process Of ZrO₂/Al-Mg Composites Based On 3D Printing Extrusion Freeform Fabrication

Interpenetrating Phase Composites?IPCs?utilize the special structure of porous ceramic phases and the possible interface reaction with metal phases to obtain metal/ceramic composites with higher bonding strength.Compared with traditional metal matrix composites reinforced by particles and fibers,interpenetrating network structure composites,due to their special structure,are beneficial to quickly disperse and transfer the stress concentrated on points or surfaces in a spatial range,which can greatly Improve the bearing capacity of composite materials.As a new type of additive manufacturing technology,3D printing technology can prepare parts with complex shapes and high precision.At the same time,it can also prepare parts with special structures through artificial design,which greatly expands the scope of application of materials.In this thesis,the 3D printing technology is used to prepare the ZrO₂ preform,combined with the pressureless infiltration process,the interpenetrating network structure ZrO₂/Al-Mg composite material is prepared.The main research results of the infiltration process and the structural properties of the composite materials are as follows:?1?The ZrO₂ preform with a network structure was successfully prepared as a reinforcement of the composite material by 3D printing technology.The experimental results show that when the diameter of the extrusion head is 0.6mm,0.8mm and1.0mm,the line gap in the space network of the preform can be Controlled at0.6-0.8mm,0.4-0.7mm and 0.4-0.5mm respectively;when the lap angle between adjacent layers of the extruded yarn is 45°,although the design hole is uniform,the area of the hole's proportion is large,and when the overlap angle between adjacent layers is 60°,the design holes are not uniform.Preform with small hole's proportion per unit area and uniform pore size can be prepared in the overlapping form of 90°;the sintering temperature of the preform should be higher than 1200?,and when the temperature is lower than 1200?,the sintering bond between ZrO₂ particles is weak,and the strength of the preform is low.?2?The experiment adopts the pressureless infiltration process to prepare the interpenetrating network structure ZrO₂/Al-Mg composite material.The infiltration temperature,infiltration atmosphere,and Mg content in the alloy are three important factors that can achieve infiltration during the infiltration process.The increase of the infiltration temperature promotes the occurrence of infiltration.When the infiltration temperature reaches above 900?,the Al-Mg alloy can be well infiltrated in the ZrO₂preform,but the increase of the infiltration temperature will bring about the deformation of the preform and the metal matrix due to the problem of volatilization,the appropriate infiltration temperature is 900-950?;infiltration atmosphere is infiltration under vacuum and air atmosphere,only weak infiltration occurs under argon atmosphere,while infiltration under nitrogen atmosphere is good,Therefore,during the infiltration process,nitrogen participates in the necessary reaction to promote the infiltration;the increase of the magnesium content in the alloy can also promote the occurrence of infiltration.When the magnesium content is higher than10wt.%,The infiltration effect will be abrupt,The infiltration effect is obvious,but at higher magnesium content,although infiltration occurs well,but due to the excessively high magnesium content in the metal liquid,the metal liquid volatilizes seriously in the metal process.At high Mg content,Al₃Mg₂ hard and brittle phase will be formed,which seriously affects the performance of the composite.Studies have shown that the activity[Mg]in the alloy plays a key role in infiltration.?3?An obvious reaction occurs at the interface of the composite material.The microscopic appearance is the metal phase?bulk material?transition layer?ceramic phase.The interface generates Al_0.1Zr_0.9O_1.95,Zr_0.875Mg_0.125O_1.875.875 replacement solid solution and Al₃Zr,which make the metal phase and ceramic phase mechanically mesh together,and the interface bonding strength is improved.When the sintering temperature of the preform is low,due to the low strength of the preform,the preform will break during the infiltration process.When the sintering temperature of the preform is 1490?,the preform is intact during the infiltration process.?4?The hardness of the composite material is significantly better than that of pure Al-Mg alloy.The mechanism is that the interpenetrating network structure of the composite material improves the hardness and other properties of the composite material to a large extent;during the friction process,the protruding ceramic reinforcement reduces the effective contact area of the friction pair and the base material,increasing its wear resistance.Experiments show that the wear mechanism of composite materials is a combination of abrasive wear and adhesive wear,with abrasive wear mainly.The experimentally measured hardness of the composite material is 196.5HV,and the wear rate is 6.4×10^-5g/?N·m?.