Study On Microstructure And Properties Of In-situ Prepared TiB₂ Particles Reinforced Aluminum Matrix Composites

In-situ TiB₂ particle reinforced aluminum matrix composites have low density,high specific strength,low expansion coefficient,high resistance to fatigue,and elevated temperature,etc.The Villiaumite mixture?KBF₄+K₂TiF₆?reaction method was used to prepare in situ self-generated TiB₂ granule reinforced aluminum matrix composites,which was mixed by adding KBF₄ and K₂TiF₆ into molten cast aluminum.Through the pyrolysis reaction of villiaumite salt,TiB₂ granule was generated in situ in aluminum solution,so as to obtain in situ self-generated TiB₂ granule reinforced aluminum matrix composites.However,in the preparation process of this method,due to the decomposition of KBF₄ villiaumite salt at high temperature,a large amount of highly toxic smoke is generated,which causes environmental pollution.At the same time,a large amount of heat is released from the reaction,which makes the reaction process difficult to control,thus generating a large number of highly corrosive by-products.To solve these problems,ZL109 and JB-3 cast-aluminum alloys were used as the matrix materials.In this paper to prepare in-situ self-generated TiB₂ particle reinforced aluminum matrix composites by improving the reaction method of traditional mixed salt method,the influence of the preparation process on the microstructure and mechanical properties of the composites was studied.The main research contents and results are as follows:1.The thermodynamics and reaction mechanism of the reaction system Al-K₂TiF₆-KBF₄ are analyzed.The results show that the reactions,2KBF₄?10?3Al?AlB₂?10?2KAlF₄,K3 ₂TiF₆?10?13Al?3TiAl₃?10?K₃AlF₆?10?3KAlF₄,and AlB₂?10?TiAl₃?TiB₂?10?4Alcan be spontaneously occur at the temperatures in the range of 200K-1200K,and the spontaneous reaction tendency increases with the increase of temperature;However,TiB₂ particles cannot be obtained by adding AlB₂ and Al₃Ti mixed particles in the melt aluminum.2.Using ZL109 as matrix material and Al-KBF₄ and Al-K₂TiF₆ as reaction systems,AlB₂/ZL109 and Al₃Ti/ZL109 composites were prepared,respectively.The effects of the preparation process on the microstructure of the composites were studied.The results show that AlB₂ particles in spherical and block-like shapes are evenly distributed in AlB₂/ZL109 composites with an average size of 5?m.While for the Al₃Ti/ZL109composite,the Al₃Ti particles are in rod,block and rod shapes with an average particle size of 15?m,which are dispersively distributed in the matrix.The process parameters for the preparation of the composites are optimized to be the melting temperature of800?,mixing time of 20 min and the holding time of 30 min,the pouring temperature of 750?.3.The TiB₂/ZL109 composite was prepared by the reactions of Al-KBF₄ and Al-K₂TiF₆ step by step,and the microstructure and mechanical properties of the composite were studied.The results show that the microstructure of the composite is fine with the TiB₂ particles in block-like shape evenly distributed in the matrix.The average size of the TiB₂ particles is about 1?m.The tensile strength of the as-cast TiB₂/ZL109composite at 25? and 360? are 167 MPa and 71 MPa,respectively,which is increased by 31.4%and 57.7%,respectively,in comparison with the matrix alloy.Moreover,the composite exhibits a high wear resistance.4.By adding K₂TiF₆+AlB₂ into the melting JB-3 alloy,the TiB₂/JB-3 composites were prepared,and the microstructure and mechanical properties of the composite were studied.The results show that the TiB₂ particles can be produced in situ through the reaction between K₂TiF₆+AlB₂+Al,and theTiB₂ particles are in shape of regular disk with the average size of about 1?m,which evenly disperse in the matrix.The tensile strength at 25? and 360? of the composite after T6 heat treatment are 239 MPa and 116.3 MPa,respectively,which increased by 16.59%and 36.4%,in comparison with the matrix alloy in T6 state.Moreover,the composite exhibits a high wear resistance.