The Microstructures And Properties Of In-Situ Prepared Mg₂Si_p/Mg-Al Matrix Composites And Its' Extrusion Deformation

in-situ reaction. The effects of the traditional solidification,extrusion and reciprocating extrusion and different heat treatment on microstructures and properties of the composites were investigated. The microstructures and phase constitution of the composites which were prepared by different techniques were studied by optical microscope, scanning electronic microscope, X-ray diffraction and differential thermal analysis. The mechanical properties of the composites were measured by hardness and tensile tests, and the thermal expansibilities of all composites prepared by different techniques were also tested by thermal mechanical analysis. The conclusions are as follows:1. AS93, AS96 and AS99 magnesium matrix composites were prepared by adding Al-Si intermediate alloy into magnesium alloy melt. The microstructures of these composites series are composed ofα-Mg matrix, dendritic or polygonal Mg₂Si phase andβ-Mg17Al12 phase.2. After solution treated composite ingots are extruded, complete recrystallization of AS93 matrix has happened; broken and refined Mg₂Si phases are distributed strippedly along direction of extrusion. AS96 has only partial recrystallization; the extruded and broken Mg2Si are distributed strippedly in form of comparatively large block along direction of extrusion. Basal body of AS99 is extruded and elongated into strip tape, equiaxed crystals aren't discovered in the basal body; the extruded Mg₂Si only are extruded and broken, but not separated.3. The uniform and refining microstructures which Mg₂Si particles uniformly distribute inmaybe obtained through reciprocately extruding solutioned Mg₂Si/Mg-Al matrix composites. As RE passes increase, Mg₂Si phases are broken and refined gradually; the size of the basal body crystal grain also diminishes gradually. The size of the basal body crystal grain of RE-12P is less than 10μm, equiaxed Mg2Si particles which are less than 20μm distribute uniformly in the basal body. 4. RE can greatly improve mechanical properties of as-cast Mg₂Si/Mg-Al matrixcomposites. As RE passes increase, room temperature and elevated temperature tensile properties, compressive property and hardness are improved greatly.