Preparation,microstructure And Mechanical Properties Of In-situ TiB₂/2024Al Composites Fabricated By Ultrasonic Assisted Squeeze Casting

Metal matrix composites have been developed rapidly in recent years due to their excellent comprehensive properties and strong design performance.The composite with Al or its alloy has excellent properties,such as high specific strength,high temperature resistance,wear resistance and so on.It is widely used in the field of structural parts.In situ synthesis is widely used in the preparation of composite materials.The wettability between the reinforced phase and the matrix prepared by in situ method is better and has excellent high temperature mechanical properties.However,the existing preparation methods are difficult to solve the two problems of fine particle agglomeration and the decrease of ductility after the introduction of second phase,Therefore,the process control of composite materials is very important.Under this background,the research of preparation,microstructure and mechanical properties of in-situ TiB₂/2024Al composites fabricated by ultrasonic assisted squeeze casting was carried out.The appropriate melt preparation parameters were obtained by studying the ultrasonic melt process of in-situ TiB₂/2024Al composites;the composites were prepared by ultrasonic assisted squeeze casting and their microstructure and properties were studied;the heat treatment mechanism and strengthening mechanism of TiB₂/2024 composites were studied,and the distribution of enhanced particles was predicted.The main research results are as follows:In the melt preparation stage,when the reaction temperature is 850?,the Al-Ti mesophase is fully dissolved to form a thermodynamically stable TiB₂ enhanced particle;High energy ultrasonic treatment of 15min can effectively inhibit the agglomeration of enhanced particles and promote their uniform distribution;With the increase of the mass fraction of the reinforcing phase,the matrix structure was gradually refined and the properties of the material were improved.Squeeze casting can significantly increase the strength of composite materials but reduce the plasticity of the materials,when the pressure was 150 MPa,the tensile strength of the materials was increased by about 40%,but the elongation was reduced by about 40%compared with the gravity casting parts;Ultrasonic vibration during solidification can improve the plasticity of composites,but has little effect on the strength of composites;The composite material with better mechanical properties can be obtained by ultrasonic assisted squeeze casting,the elongation and the strength of the composite material can be both improved.The hardness of TiB₂/2024 composites increased significantly after heat treatment,about 40%higher than that before heat treatment.The main strengthening mechanisms of composites include thermal mismatch strengthening,Orowan strengthening,grain refinement strengthening and load transfer strengthening,The enhancement effect is related to the particle size distribution,and the distribution of enhanced particles can be predicted by comparing the theoretical value with the actual value.It is found that increasing the number of reinforcing particles in the grains is the key method to improve the comprehensive properties of particle reinforced composites.The study on the solidification behavior of TiB₂/2024 composites is of great significance for obtaining high strength and high plastic aluminum matrix composites and expanding the application prospect of aluminum matrix composites.