Influence du type de renfort et des reactions chimiques aluminium-carbure de silicium sur les proprietes des composites a matrice metallique

This thesis deals with the effect of the type of reinforcement and of the chemical reactions between Al and SiC, on the properties of MMC. We had a particular interest in the matrix of the ternary systems Al-Mg-Si such as AS7G03 and 6061 commercial alloys. We have also studied some binary alloys Al-5% and Al-1% Mg. The first part covers the subject of processing of MMC's by the compocasting technique. Our work assesses the role of semi-solids state in facilitating the incorporation of the reinforcement. Other factors also affect the elaboration of aluminium matrix-silicon carbide composite such as surface oxidation of SiC and the presence of Mg in the melt.; The second part of our work consists of the characterization of product, of the reaction between the different matrix and silicon carbide in the as-received condition or after artificial oxidation. For as-received particles after elaboration no reaction has occurred between the molten aluminium and the silicon carbide. However, prolonged holding at elevated temperature gives rise to extensive formation of Al{dollar}sb4{dollar}C{dollar}sb3{dollar}. For oxidized particles the silicon layer surrounding the silicon carbide reacts with the molten alloy to form Mg rich polycrystalline oxide. In the case of low magnesium concentration this oxide layer is mainly composed of spinel (MgAl{dollar}sb2{dollar}O{dollar}sb4{dollar}) and for the higher 5% Mg level MgO is formed. Those oxide layers can protect the SiC against molten aluminium attack acting as a diffusion barrier.; Those reactions between silica and Al-Mg alloy consume some magnesium from the melt and brings Si into the metals. These composition changes greatly affect the age hardening behavior of the matrix. For example it is possible to generate age hardening behavior on an Al-1% Mg matrix composite which is not hardenable without the effect of the reaction with oxidized particle.; The last part of this thesis treats the mechanical properties of Al-1% Mg matrix reinforced by oxidized or as-received particles of different shapes (platelets, sphere and angular particles). The main effect of the surface oxidation of particles is caused by the hardening of the matrix resulting from the silicon rejection of the interface reaction. The failure of the material is brought about by cavities germination.; In the case of very soft matrix, cavities are initiated by ductile mechanism in the matrix. As the hardness of the matrix increases, the number of broken particles increases but for the hardest material rupture occurs as a result of the failure of the interface. (Abstract shortened by UMI.)...