Study On Technique Of Preparing Aluminium Alloy Semi-solid Slurry

The first, as well as crucial, step of semi-solid processing is to prepare semi-solid slurry. This paper represents a novel technique of preparing ZL101 aluminium slurry, which takes advantage of mechanical vibration. The slurry prepared using mechanical vibration has a mean size ofαgrains of 60μm~100μm, with a near-spherical configuration, and the solidoid proportion varies from 5% to 65%, which could be applied to many kinds of rheological process.Firstly, the mechanical vibrator used to preparing semi-solid slurry and a die mold are designed and fabricated. Vibrating amplitude and frequency are adjustable, through adjusting eccentric block and frequency converter. The die mold matches horizontal cold chamber die casting machine, and its cavity is designed according to the die casting test bars.Secondly, this paper studies convection of liquid under mechanical vibration. A water-polystyrene model is used, and it is found that as the amplitude of vibrating equipment goes up, the amplitude of free surface of liquid increases as well, the whole liquid bulk moves more violently; while as the frequency of vibrating equipment increases, the amplitude of free surface goes down, and the liquid moves much faster. Generally speaking, the free surface of liquid in the cup moves most violently, and the energy is decreased gradually when transmitted downwards.The mechanism of formation of non-dendritic grains is investigated. A water-30%wt. NH4Cl model is used to study the influence of mechanical vibration on nucleation and crystal growth, which shows that numerous equiaxial grains generates under the circumstance of vibration and overcooling, compare to that of coarse dendritic ones without vibration. Under the convection prompted by mechanical vibration, formation of non-dendritic grains attributes to the equiaxial grains generated as well as convection, which leads to grains'movement and growing by all directions, then the grains grow up to be near-spherical in the end.This paper also studies relationship between experimental factors(including frequency and amplitude of vibration, slurry holding time, holding temperature, pouring temperature and adding 0.2%wt.Al-5Ti-B additive) and slurry quality. Mean diameter of grains decreases as amplitude and frequency go up, while increases as holding time and holding temperature go up; mean configuration coefficient of grains increases as amplitude and frequency go up, while decreases as holding temperature goes up, while increases at an early stage and decreases later as holding time goes on, and it reaches the summit when being held at a temperature of approximately 605℃; proportion of solidoid increases as vibrating frequency goes up. It is found as well that the higher the pouring temperature is, the worse the slurry becomes. What is more, adding 0.2%wt.Al-5Ti-B helps to fineαgrains.The influence of experimental factors on quality of casting is studied in the end, according to which the combination of these factors leading to a best outcome is represented. Vibrating frequency and holding temperature have complex influence on the quality of casting, while as holding time goes up, the quality goes down. The best combination of experimental factors, which is feasible for rheological die casting is chosen as: vibrating frequency of 41.7Hz, and holding time 3min, holding temperature near to 605℃.