| Semi-solid forming (SSF) method is one of the most promising near-net-shape forming technologies in the 21st century. With its high efficiency, energy-saving, near-net-shaped forming production and high-performance products, and many other advantages, it has received extensive attention. In semi-solid processing technology, the key to SSF is fabricating the semi-solid materials with fine, uniform and spheroidal microstructure.ZL201 alloy is an important heat-resisting casting alloy with high strength and high mechanical properties at high temperature. Its cutting performance is good; processing surface is smooth; rich copper phase is heat-resisting; smelting technology is simple. It is mainly used in the manufacture of parts working at high temperature, and widely applied in the automotive industry, aerospace industry etc. But this kind of alloy's casting performance is poor, easy to generate heat crack, and it has big density and low resistance to corrosion.In this paper, ZL201 alloy is the object of the study, ZL201 alloy semi-solid slurry is prepared by nearby-liquidus with electromagnetic stirring casting technology. The experimental results show that, when electromagnetic stirring is imposed on ZL201 alloy melt at liquidus temperature, the microstructures of ZL201 alloy slurry are fine and near spherical grains. With the intensity of electromagnetic stirring and cooling increasing, grains growing fine and uniform. Electromagnetic stirring causes strong convection in the melt, so the melt temperature field and composition are uniform, and the condition against grain preferential growth is formed. When the melt temperature drops to the liquidus level, the whole melt enters the state of undercooling immediately, and a large number of nucleation is formed. Under the condition that the melt solute is well distributed, grain grows in all directions at the similar speed, and the grain can grow nearly spherical rapidly.The preparation of ZL201 alloy semi-solid slurry is prepared for rheological die forging forming.The microstructures and properties of ZL201 semi-solid rheological die forging are studied. The results of experiment show that, Because of the nearby-liquidus pouring and the role of electromagnetic stirring, the temperature and components of alloy melt is uniform.When ZL201 alloy melt is poured into the self-made mould, the alioy melt cool rapidly, a large number of atomic groups grow quickly. In the process of semi-solid die forging, the pressure increases the speed of solidification, reduce the melt temperature gradient and promote composition undercooling. Pressure and the intense flow of melt in the mold is help to accelerate the speed of heat dissipation, prevent bubbles and porosity. The pressure makes the forgings generate plastic deformation during solidification, break dendrite arms to fragments, so the microstructures and mechanical properties of the forgings are improved greatly.T5 heat treatment is used in the experiment of ZL201 forgings heat treatment, when solution temperature is 535±5℃, aging temperature is 175±5℃; solution time is 8h and aging time is 10h, the hardness value of the sample is 142.65HV, which is higher than other samples with other heat treatment. The results show that alloy forgings which its slurry with the electromagnetic stirring, alloy elements are uniform in the microstructure, and the electromagnetic stirring improve supersaturation of Cu, Mn and Ti element in the matrix, when alloy forgings under aging treatment, the size of precipitation phases become small, and uniform distribution, the number of precipitation phases increases.This study is under the circumstance of the ZL201 alloy composition does not change, using semi-solid slurry which prepared by nearby-liquidus with electromagnetic stirring for rheological forging, and using T5 heat treatment, improving the microstructure and mechanical properties of alloy forgings, increasing the using value of ZL201 alloy. |
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