Wrought Aluminum Alloy Semisolid Slurry Microstructure Formation In Self-inoculation Method Process And Its Rheo-Squeeze Casting

Semi-solid forming technology combines the advantages of traditional whole liquid casting and whole solid forging, provides a new solution to the complicated shape wrought alloy parts near net shape forming.2024wrought aluminum alloy as the research object in this thesis, semisolid slurry was prepared by self-inoculation method, micro structure and evolution regularity of the primary solid phase in the slurry are investigated. The solidification process of non-dendrite primary grain in self-inoculation method process is analyzed. Wheel hub trial production was formed by applying direct rheo-squeeze casting technology, and the microstructure and forming defects of those semisolid wheel hubs were analyzed.The microstructure evolution of2024wrought aluminum alloy slurry during continuous cooling and isothermal holding was investigated by a simple technique of water quenching. Results show that during the continuous cooling course, solid fraction, average particle size and shape factor increases continuously with decreasing temperature. The increase of solid fraction during continuous cooling was dominated mainly by the precipitation of solid-phase particles in the early stage, and by the growth of solid-phase particles at last. The evolution process of isothermal holding can be divided into three steps:disaggregation of the chain structure, mergence and coarsening, and the final ripening of primary particles. While in the isothermal holding stage, solid fraction of the slurry fluctuated at the corresponding values, particle size of the primary solid phase increased continuously, and the shape factor decreased firstly, then increased and finally decreases to a value between1.3-1.4. These primary solid particles grew by obeying the LSW kinetic law in the whole isothermal holding process, which suggests coarsening by Ostwald ripening.Solidification process analysis of primary phase in the semisolid slurry prepared by self-inoculation method shows that, a intense temperature fluctuation was burst into the alloy melt while the self-inoculants particles added, and a compulsory homogeneous nucleation formed. Inclined plate multi grooves diverter wall play a role of heterogeneous nucleation basement, a lot of rosiness free crystal was formed by the convection on the diverter. High nucleation rate and crystal nucleus growth and survival are the key of the self-inoculation method slurry preparation process. The formation of free grain and it size grew up were influenced by undercooling in the melt and interaction between the primary crystal.According to experimental equipment and preliminary research foundation, The experimental process parameters of2024aluminum direct rheo-squeeze casting were formulated. Slurry pouring temperature, mold preheating temperature, squeezing pressure, squeezing speed, dwell time, and graphite lubricant were confirmed.2024wrought aluminum alloy wheel hub trial production was formed by applying direct rheo-squeeze casting technology. The microstructure, element distribution characteristics and forming defects in those semisolid wheel hubs were analyzed.