Study On Rheo-squeeze Casting Of Al-Cu Alloys

Semi-solid rheo-forming process is considered as one of the new formingtechnologies, which can be used to make thin-wall parts with high strength and lightweighting. It has attracted the attention of the society in the low-carbon economy trend forits low energy consumption and simple process. Al-Cu alloy is widely applied in manyfields, and how to further improve the performance of the Al-Cu alloy components is veryimportant. This research is focused on the Al-Cu alloy slurry preparation by indirectultrasonic vibration and the properties of rheo-squeeze casting components. Themechanism of indirect ultrasonic vibration is also discussed.The semisolid slurry of AlCu5MnTi alloy was prepared by indirect ultrasonicvibration (IUV), in which the horn was vibrated under the outside of the metallic cupcontaining alloy melt. The chemical compositions of the AlCu5MnTi alloy are Cu4.8%,Mn0.8%, Ti0.3%(mass%) and Al balance. The research mainly included the effects ofIUV temperature and time on the morphology of the semisolid slurry, and the distributionof primary crystals in the whole cup under the IUV. The results indicate that after applyingthe IUV for60s near or above the liquidus temperature, the semisolid slurry with grainshape coefficient of0.56and average grain diameter of67μm can be obtained. During theIUV time of60s, grain shape coefficient and average grain diameter are steadilyincreasing, from46μm to67μm and from0.42to0.56respectively. But the grain shapecoefficient declined to0.53at80s. The grain distribution of the whole cup isfundamentally uniform, and the average grain diameter of the top and the bottom isslightly bigger than the middle. A large quantity of free grains is observed near the cupwall within1to3mm to the edge, which indicated that IUV had the effect ofhigh-frequency mechanical vibration. Therefore, indirect ultrasonic vibration combines theeffect of both ultrasonic vibration and the high-frequency mechanical vibration.The semisolid slurry was formed by direct squeeze casting (SC). The effects ofapplied pressure, mould temperature and heat treatment on microstructure and mechanicalproperties of rheo-squeeze casting (RSC) AlCuMnTi alloy were studied. The results show that with the pressure increased from25MPa to100MPa, the average particle diameterdecreased from38μm to30.7μm, while the average shape factor increased from0.52to0.66. With the mould temperature increased from220℃to320℃, tensile strength andelongation increased firstly and decreased afterward. Under the condition that the pressurewas100MPa and the mould temperature was270℃, components achieved the bestmechanical properties after T5heat treatment. The tensile strength and elongation was326.5MPa and11%respectively, which were improved by6.5%and47%respectivelycompared with conventional squeeze casting components. The refinement andspheroidization of the grain are mainly attributed to the cavitation effect and acousticstreaming by the IUV. IUV homogenizes the solute field and eliminates themacrosegregation, resulting in higher mechanical properties. On the other hand, themechanism of grain refinement by pressure was also studied. The grain refinement wasmainly attributed to the increase of the heat transfer coefficient between the componentand the mould, rather than the change of the alloy liquidus temperature.