Forming And Properties Of SiCp/AZ91 Magnesium Matrix Composite Tubes

SiCp/AZ91 magnesium matrix composite ignots with the SiC particles average size of 10μm and volume fraction of 20% were fabricated by stir-casting technique. The deformation processes from SiCp/AZ91 magnesium matrix composite ingot to tube were simulated by software DEFORM2D and the real tubes with two extrusion radios were processed successfully. The microstructures of the materials were examined by optical microscope (OM) and scanning electron microscope (SEM). The tensile properties, impact resistance behaviors, fracture toughness and damping behaviors of the ingot and tubes were tested. The basal plane texture of the matrix of the composite was measured qualitatively by the method of X-ray diffraction.The distributions of SiCp were almost the same in different parts of the big ingot and there was just tiny precipitation of SiCp in the bottom of the ingot. The simulation of the hot extrusion showed that large extrusion speed could break the outside wall of the tube. If the tubes were extrused by low speed, the friction condition had tiny effection on the forming process.We got a perfect extrison technology with the extrusion speed 1mm/s and extrusion temperatue 400℃by which the tube didn't present periodic surface cracksDynamic recrystllization took place during the extrusion. The extrusion improved uniformity of SiC particle distribution and as the extrusion radio increased, the uniformity was better. There was strong basal texture in the matirx of the extrused tube, with the basal plane parallel to the extrusion direction and paralle to cylinder of tube. The intensity of basal texture in the matirx increased as the extrusion ratio increased.Hot extrusion enhanced the mechnical properties significantly because it could eliminate particle segregations in as-cast composites,improve particle distribution uniformity and increase the bonding strength between the SiC and matrix. Hot extrusion reduced the damping properties in room temperature but enhanced high-temperature damping performance of the composites.After solution and aging treatment, Mg17Al12 appeared as net-distrubution. Heat treatment enchanced the yield strength and ultimate tensile strength but reduced the fracture toughness of the tube.