Semi-solid Microstructure Evolution And Thixoforging Of As-cast TiB₂/Al Composites Billet

Aluminum matrix composites have become a high-performance light alloy material urgently needed by the rapid development of military defense,aerospace,rail transit and other fields,due to its many excellent properties.At present,the technology of semisolid thixoforming of particle reinforced aluminum matrix composites is facing a problem about the preparation of semi-solid billet.In this context,the research on microstructure evolution during semi-solid remelting and thixoforming of TiB₂/2024 Al composite as-cast billet is carried out.Specific research contents include: TiB₂/2024 Al composite with fine equiaxed crystal structure was prepared by optimizing the process parameters of liquid forging.Effects of semi-solid remelting process parameters on microstructure evolution of TiB₂/2024 Al composites under conventional thermal radiation heating and induction heating.Microstructure evolution mechanism of semisolid remelting of TiB₂/2024 Al composites.And study on thixoforging of TiB₂/2024 Al composites.Firstly,in-situ TiB₂/2024 Al composites were prepared by ultrasonic assisted liquid forging.The microstructure of the billet was improved by changing the casting temperature.Casting temperature determines the solidification process of composite melt under the action of liquid forging pressure.When the casting temperature is 730?,the composite melt will solidify immediately under the undercooling provided by the pressure and form a cast microstructure with fine equiaxed grains.And the microstructure uniformity of composite ingot is well.Then the semisolid remelting test of TiB₂/2024 Al composite as-cast billet was carried out by conventional thermal radiation heating.After semisolid remelting,the microstructure of composite as-cast billet with 730? casting temperature has high roundness and has high uniformity.With the extension of the heat preservation time of remelting,the average grain size of semisolid microstructure increases.Semisolid remelted grain coarsening mechanisms include grain consolidation growth mechanism and Ostwald ripening.When the remelting temperature is low,the grain growth mechanism was dominated by the grain consolidation growth mechanism.As the remelting temperature increases,the grain coarsening is dominated by Ostwald ripening mechanism.The mechanism of ultrasonic vibration on semisolid microstructure needs further study.At last,semisolid remelting and thixoforming of TiB₂/2024 Al composite as-cast billet were carried out by induction heating.The optimal semisolid remelting process parameters were determined as 628? and holding for 5 min and the average grain size and shape factor of semisolid microstructure were 67.1 m and 0.84 respectively.The thixoforging of TiB₂/2024 Al composite was carried out with the optimum remelting parameters.And a certain type of engine connecting rod with good surface quality was formed.The yield strength of the big end of the connecting rod and the connecting rod body were increased by 9.0% and 11.8% respectively compared with that o f the as-cast billet,and the tensile strength was increased by 7.7% and 6.3%,and the elongation was increased by 6.5% and 10.8,respectively.In this paper,the preparation of TiB₂/2024 Al composite as-cast billet,the semisolid remelting of composite as-cast billet under conventional radiation heating and rapid induction heating,and the semisolid thixoforging were studied.A method for preparing a composite billet with fine non-dendritic microstructure,microstructure evolution mechanism of semisolid remelting of composite under conventional thermal radiation heating,microstructure evolution of semisolid remelting under induction heating condition,and the process of semisolid thixoforging were proposed.A theoretical and experimental basis is proposed for the preparation of semisolid billet of aluminum matrix composites with short process and low cost,and to realize the precise forming of complex components of aluminum matrix composites.In the future,the research on semi-solid forming of aluminum matrix composites should focus on the accurate forming of complex components of aluminum matrix composites,and the corresponding relationship between semi-solid structure and the structural properties of formed components,so as to realize the collaborative control of composite thixo forging ability and properties.