Study On SiO₂p/AI-Mg Composites

In this paper, the Si02/Al-Mg composites have been triumphantly fabricated by powder metallurgy and thermodynamics, kinetics, microsti-ucture of interface, characteristic of friction and wear, density, hardness, conductivity, compression strength et al. of the composites have also been studied. The reaction-diffusion mechanism can be described by 憀ayer by layer reaction mechanism?and diffusion mechanism. the main reactions are as follows: 1 1 in particles: Al + Mg + Si02 = ?MgAI2O4+ Si AG~X) =-219 KJ/mol 2 2 or 2Mg + Si02 2MgO + Si AG~X) -172.6 KJ/mol 4 2 ?Al + Si02 Al203 + Si AG~~ =~-2 1 OKJ/mol 3 3 9(X) MgO + A1203 = MgAI2O4 AG0 =-28KilmoI 900 1 1 and Ai+ 桟u+Si02= ?CuAl2O4+Si 2 2 in Al-Mg matrix 2Mg + Si = Mg2Si 3Mg + A1203 = 3MgO + 2 Al AG~ =-43KJ/mol 3 3 1 桵g +A1203= ?MgA12O4+ 桝l AG~~ =-I3KJImol 4 4 2 According to our calculation about 16 5?8.4wt% MgAI2O4, O.7lwt%CuAI2O4 and a little MgO and Mg2Si or Si are generated in particles, all Si02, however, have been exhausted, In Al-Mg matrix about 11 .7wt%Mg2Si, 3桽wt%Si and 0 52wt%MgO are produced and Mg doesn抰 exist any longer. In the course of reaction about 2.8wt% Mg. 7.Owt% Al and 0 25wt% Cu diffuse from matrix to particles and about 9.7 Iwt% Si (as many as 97 1% of Si contents in primary 5102 particle) and about 0 26wt% 0 (as many as 2.6% of 0 contents in primary Si02 particle) diffuse from SiO? particles to Al-Mg matrix Under dry sliding wear conditions, the composites is suitable to work below the load of 200N, yet under lubncated sliding friction conditions, the largest ~憃lume loss isn抰 more than 0.8mm3 at the load of I 794N and the friction factor is less than 0.14, so this kind of composites can run in harshness conditions such as larger load in lubricated friction conditions. The wear rate of lubricated friction is less 2梸3 order of magnitude than that of dry friction, which shows the composites are perfect for lubricated friction conditions. In dry friction conditions the wear mechanism of the composites takes adhesive wear as the dominant factor below 294N, thereafter, gradually transforms into plow-type abrasive wear and slight adhesive wear along with increasing load; And in lubricated friction conditions the wear mechanism of the composites is light abrasive wear and little adhesive wear. The composition of inferior layer of dry friction is different from that of lubricated friction. The inferior layer of dry friction is composed of four parts: compound layer, broken layer, deformed layer and prototype structure layer, whereas the inferior wear layer of lubricated friction consist of three parts except for broken layer.