Effect Of La₂O₃ On In-situ Reaction Of Al-Ti-C-CuO System In Aluminum Alloy Melt

In order to reduce or eliminate the large-sized strip-like phase Al₃Ti which is easily formed in the in-situ reaction of the Al-Ti-C-CuO system,the rare earth oxide La₂O₃ is added to form the Al-Ti-C-CuO-La₂O₃ system.The Aluminum Matrix Composites were manufactured by in-situ reactive near liquidus cast of La₂O₃ powder,aluminum powder,CuO powder,Ti powder,graphite powder with 6063 aluminum alloy as the matrix using the in-situ reaction method.The Optical Microscope,X-Ray Diffraction,Differential Scanning Calorimeter,Scanning Electron Microscope,Energy Dispersive Spectroscopy and Transmission electron microscope were utilized to study the phase size,morphology,distribution of the in-situ reaction products and its interface structures with the Al matrix.The specific results are as follows:When the melt preheating temperature is 1000°C,the reactant powder mixing time is 60 min,the precast block molding pressure is 10MPa,and the reactant molar ratio in the preform is Al:Ti:C:CuO:La₂O₃=4.8:1.0:1.2:1.0:0.008?the content of La₂O₃ is 0.6wt.%of the content of the precast block?,the additions of precast block is 20wt.%of the mass of the Al matrix,the aluminum matrix composites with better shape and uniform distribution of in-situ reaction products are manufactured.After La₂O₃ is added to the Al-Ti-C-CuO system,the in-situ reaction process,the size and distribution of the in-situ reaction products in the system change significantly.La₂O₃ reacts with C to form LaC₂and CO.LaC₂ reacts with Ti in the melt to form TiC and[La],and[La]reacts with Al and Ti in the melt to form a new rare earth phase Ti₂Al₂₀La.Therefore,the reactions between Al reacts with C and Ti to form Al₄C₃ and Al₃Ti are prevented.The 120?m Al₃Ti phase transforms into a 20?m Ti₂Al₂₀La phase and the size of Al₂O₃ and TiC particles reduces from 5?m to 1?m and 1?m to 0.5?m,respectively.TiC particles act as nucleation cores to promote nucleation and Al₂O₃ particles pin the grain boundaries to hinder grain growth during solidification.TiC and Al₂O₃ particles refine grains together.Moreover,the fluidity of the whole matrix melt is improved and the in-situ Al₂O₃ and TiC particles are dispersed in the matrix to dispersion-strengthen the aluminum matrix composite.The aluminum-based composite material follows the lowest energy principle during solidification.At the interface structure between the in-situ products and the Al matrix,the crystal plane of the Al matrix first crystalized is the close-packed surface?111?.It is found that the in-situ reaction products have the following orientation relationship with the Al matrix:TiC?200?//Al?111?and its interface is in a semi-coherent relationship;Al₂O₃?112?0?//Al?111?and its interface is in a coherent relationship.Al₂O₃?011?2?and?101?2??form a non-coherent interface with the Al matrix;?-Al₂O₃?101?3?,?0006?,?1?013?forms a non-coherent interface with the Al matrix?111?plane;The coherent interface is formed between the Al₃Ti?112?crystal plane and the Al matrix?111?crystal plane,and the interface between the Al₃Ti?204?crystal plane and the Al matrix?111?crystal plane is in a non-coherent relationship;Ti₂Al₂₀La?440?//Al?111?and its interface is in a semi-coherent relationship and the Ti₂Al₂₀La?311?//Al?111?forms a non-coherent interface.