Fabrication Of In Situ Al₂O₃Particle Reinforced Al Matrix Composites

In situ Al2O3particle reinforced Al matrix composites have clean interface and highinterfacial bond strength with Al matrix, so they have good comprehensive perfo rmanceand attractive application prospect. Among all the in situ methods, contact reactionprocess and direct melt reaction process are simple technological processes. However, theoxide powder is not easy to disperse and get into the melt, and the temperature of thereaction is usually high. So it is necessary to improve the wettability between oxidepowder and Al melt, and decrease the temperature of the in situ reaction. In this paper,the preparation technology of in situ Al2O3particle reinforced Al matrix composites wasstudied, which is based on the contact reaction and direct melt reaction of Al-CuO andAl-SiO2reaction system. We initiate the technology to bring the indirect ultrasonictreatment into Al-CuO reaction system.First, the composites were fabricated by contact reaction process using Al-CuO-SiO2reaction system. The results show that when there is no Al powder mixed in the CuO-SiO2powder (mass ratio of CuO and SiO2is2.5:1), the in situ reaction is hard to happen below825℃; after adding some Al powder into the powder, the in situ reaction could happen.The optimum powder proportion of Al/(CuO+SiO2) is about1/5. The reduction ofweight or briquetting pressure of preformed block can’t improve the dispersion of thereaction product. And it is the same case when the powder is wrapped in aluminum foilinstead of briquetting, or when the content of Al powder in mixed powder increases. Someof the Cu produced by the reaction dispersed into melt and observed as Al2Cu phase at thegrain boundary while the other Cu remained in the slag. There are almost no Al2O3particles dispersed into the melt.Then, the composites are fabricated by direct melt reaction using Al-CuO reactionsystem. And the effects of dispersants and ultrasonic treatment on the in situ reaction werestudied. The results show that flux can adsorb and dissolve Al2O3and makes Al2O3turninto slag and separated from the melt. So the flux can’t be used as dispersant. Whenassisted with indirect ultrasonic treatment (ultrasonic power is2.6kW), the in situ Al2O3particle reinforced Al matrix composites can be synthesized successfully by direct melt reaction between Al and CuO. With ultrasonic treatment，Al2O3particles are about1~2μm in diameter and the particles distribute uniformly both in the grains and the grainboundaries. Furthermore, the quantity of Al2O3particles with ultrasonic treatment is morethan that without ultrasonic treatment. The optimal temperature of indirect ultrasonictreatment is about665~675℃. The heating and isothermal holding process after ultrasonictreatment is beneficial to the dispersion of Al2O3particles. The promotion of in situreaction is mainly due to acoustic streaming effect and acoustic cavitation effect duringultrasonic treatment. Because these two effects can improve wettability between Al meltand CuO powder and can disperse the agglomerate CuO powde r. The essence of thepromotion is the optimization of kinetic and thermodynamic environment in the reaction.