Research On Technology Of Rehoroll-Casting Forming For Semi-solid AZ91D Magnesium Alloy

Semi-solid metal process (SSM) which was born in seventys at 20st century is a new near net shape technology. And its drip molding is compaction, high mechanical property; little machining, long mould life and can make complex configuration, environment protection, energy conservation, high efficiency. So, it is more and more taken into account in all over the world.It is considered as the most potential one of metal forming technology in the 21st century.Magnesium alloy have the advantages of light-weight, high intensity ratio, high stiffness/weight ratio, high damping property and electro magnetism shielding property and so on, so recently it has acted an important role in automobile and electric industry as a weight reducing material. But the application of magnesium alloys productions most is die-casting. Die-casting has not been satisfied with the require of production colligation properties, because the thin wall accessories used in the 3C(Computer, Communication, Consumption)products and the high performance magnesium alloy accessories used in the auto products required with the processing techniques higher and higher. The processing technology of semi-solid metal has very vast development foreground. Up to date, there are seldom study on semi-solid rheocasting process and the microstructure and properties of semi-solid magnesium alloy.In this paper, the process of the semi-solid AZ91D rehoroll-casting by the semi-solid manufacturing equipment which was self-developed was researched. Near globular and nondendritic grain of semi-solid magnesium structure was made by the methods of mechanism stiring and slope. Because of the nice flow properties of the semi-solid slurry, rehoroll-casting was carried after mading semi-solid slurry. Then semi-solid rehoroll-casting magnesium strips were received. The microstructure and the properties were tested. Furthermore, the simulation experiment was carried out in computer by the finite element method. On the numerical and experimental base, the technical parameter was optimized by the orthogonal design.The result is: 1.The trial material, trial equipment, trial processing of AZ91D semi-solid magnesium rehoroll-casting were researched. The methods of making slurry used by trial were mechanism stiring and slope. The whole trial equipment was self-developed. The trial equipment was feasible indicated by trial.2. The temperature collection and control on AZ91D semi-solid magnesium rehoroll-casting were achieved via virtual instrument technology. The virtual instrument system was performe credibility, work convenience, and was capable of high precision of control temperature. This establish the foundation of practise apply for this technology.3. Effect of technics parameters of semi-solid magnesium rehoroll-casting process on microstructure via a great deal of tests was researched. The effect of stir rate, stay time, mould temperature on the size and shape of semi-solid magnesium strips structure were investigated. Consequently, the optimum technics of making sulrry and rehoroll-casting was confirm.4. The optimum parameters of mechanism stiring method and slope method were obtained by orthogonal method. The optimum parameters of mechanism stiring method were: shearing rate 500 r/min; staying time 10min; stiring time 15min; moulding temperature 560℃; The optimum parameters of slope method were: moulding temperature 630℃; lean angle 60°; slope length 0.570m; staying time 5min;5. The further hot-cold process showed: AZ91D and AZ31B semi-solid rehoroll -casting strip have a big plasticity.The cold total deformation was 28% of AZ91D. the hot total deformation was 47% of AZ91D. The hot total deformation was 57% of AZ31B.6. It was shown that heat treatment process can improve the structure and property of semi-solid magnesium rehoroll-casting strips. The technicse of heat reatment was fine when the heat treatment temperature is about 420℃. With the increasing of heat treatment temperature, the aberrated eutecticα-Mg grain increased gradually and the shape became nubby gradually,β-Mg₁₇Al₁₂ phase decreased gradually andβ-Mg₁₇Al₁₂ phase which remain a few discontinuity distribute on theα-Mg grain boundary closely approaching the equilibrium solidification structure.β-Mg₁₇Al₁₂ phase separate dispersion out from the aberrated eutecticα-Mg grain again. Which not only make the base body intensify but also nonrestrict the mechanism of transfiguration .With the increasing of heat treatment temperature, hardness in eutectic structure area will increase and then decrease, when the temperature is beyond 400℃, it will increase again, but primaryα-Mg grain hardness is nearly unchanged.7. The simulation experiment of making slurry and casting were carried out in computer by the finite element method. Coupled numerical simulation of flow and heat in rheoroll-casting for semi-solid magnesium alloys used by slope was researched. The influence of the different slope parameters( pouring temperature,length of slope,lean angle)on the flow and heat field of semi-solid magnesium alloy is analyzed. Heat field numerical simulation of roll-casting area was researched too. The optimum moulding temperature was decided by the optimum solidification point, and obtain the optimum parameters of slope: moulding temperature 630℃, lean angle 60°, slope length 0. 570m, staying time 5min.