Fabrication Of In-situ TiB₂ Particulate Reinforced Magnesium Matrix Composites

The microstructure and properties of magnesium matrix composites with in-situ TiB2 particulate reinforcement were investigated in this paper. The in-situ TiB2/Mg-Zn-Cu-Y-Zr and TiB2/Mg-Sn-Zn-Al magnesium matrix composites were prepared by self-propagating high-temperature synthesis (SHS) and semi-solid stirring casting method. The effects of Al-Ti-B precast block on the microstructures and mechanical properties of both the two alloys were studied. Besides, the electromagnetic cast and ultrasonic vibration were introduced into the preparation of the TiB2/Mg-Sn-Zn-Al alloy. And their effects on the microstructure and mechanical properties of the alloy were also studied. The research results are as follows:The analysis of XRD results indicates the existence of I-phase (Mg3Zn6Y) and W-phase (Mg3Zn3Y2) in Mg-Zn-Cu-Zr alloys with the addition of Y element. The average grain size of Mg-Zn-Cu-Zr magnesium alloy is effectively reduced from 57μm to 39μm by Y element. The ultimate tensile strength of the Mg-Zn-Cu-Zr alloy is significantly deteriorated with the increasing of Y content, which is possibly related to the continuous networks of intergranular phases and the increase of W-phase.With the addition of Al-Ti-B precast block, the gain size of as-cast in-situ TiB2/Mg-Zn-Cu-Y-Zr magnesium matrix grows, and the elongation of the alloy reduces dramatically. After the treatment of hot extrusion, the gain size decreases and the distribution of particles becomes more uniform, which result in the improvement of mechanical properties of magnesium matrix. However, the tensile strength of the alloy reduces first and then increases with the addition of Al-Ti-B precast block.The grain of the in-situ TiB2/Mg-Sn-Zn-Al magnesium matrix, which was prepared by semi-solid stirring casting method, is refined with the addition of Al-Ti-B precast block. The TiB2 particulates are well connected with the matrix. Besides, the tensile strength of alloy effectively increases. When the content of Al-Ti-B precast block is 6 wt%, the tensile strength of alloy reaches to 129 MPa which is 12% higher than that without block. The treatment of hot extrusion improves the uniformity of TiB2-The strength of the alloy is up to 290 MPa while the content of block is 4 wt.%.The structure of in-situ TiB2/Mg-Sn-Zn-Al billets, which was obtained by the EMC method, is more fine and uniform than that prepared by the die cast method. Moreover, the strength and elongation of the alloys are greatly improved and reach to 41.9% and 50% respectively.The study of the in-situ TiB2/Mg-Sn-Zn-Al magnesium matrix with the application of ultrasonic vibration technique shows that the grain of alloys is refined, and the TiB2 particulates are better dispersed than the mechanical stirring. The tensile strength of alloys reaches to 142 MPa which is 25.8% larger than that of mechanical stirring billets.