| Although China has a great resource of magnesium, the application ofmagnesium alloy stays in low-grade phase. As a result, to develop a processof low-cost and high-quality to produce thin magnesium alloy sheet, is a newchallenge to magnesium enterprises.Traditional process to produce magnesium alloy sheet is to use thecasting thick sheet to roll, involving in-process annealing, so that it is a longprocess. Due to short process, the continual casting and rolling (CCR)process is used presently to produce magnesium alloy sheet, nevertheless,the sheet is limited in the thickness and quality. This article is to develop aprocess of low-cost and high-quality to produce magnesium alloy sheetreferring to the process of CCR+ hot rolling of aluminum.Firstly, 2Cr13 and Q235 are chosen to compare the stability inmagnesium melt, and the samples of the two materials are immersed in molten magnesium alloy at 660℃for 24h, 48h and 72h. The metallographicstructures of the samples' surface are examined and the thickness of erosionlayers between the samples and the melt are measured. The curve ofthickness-duration is gained, the thicknesses of erosion layers of 2Cr13 andQ235 after 24h immersion are 46μm and 48μm respectively, and after 72hare 50μm and 107μm respectively. It is found that the erosion layer of the2Cr13 is without crack and the layer of Q235 is with crack. It is proven theflat layer has a passivating effect to the corrupting process. It is concludedthat 2Cr13 is a better choice for crucible material for its saving cost andlessening loss of breakdown of production.The pre-treatment of the CCR sheet is executed. The temperatures inthe experiment are 300℃, 350℃, 400℃and 450℃, and the immersingperiods are 2h, 4h, 6h and 8h, and the cooling ways are air cooling and watercooling respectively. The metallographic structures of samples at differentprocess are examined and the hardness is measured too. Considering thedesire of fine grain and small hardness in rolling process, the best process is:keeping 4-6h at 400℃, cooling in air. By this, the average size of the grain is10μm, and the hardness is 65HV.As the original status of material is key to the hot rolling process, and atpresent the hot rolling parameters of the CCR magnesium, sheet are notavailable, the compressing experiments are done, the sheets which arepre-treated and not are chosen to compare the effect of pre-treatment. 200℃, 250℃and 300℃are chosen for deforming temperature, the strain rates are0.1s-1, 0.01s-1 and 0.001s-1, and the strain are 0.2, 0.4 and 0.6 respectively forsheet not pre-treated at 300℃, 0.1s-1. The metallographic structures of thesheet deformed are examined, the best rolling parameter is: deforming at300℃and the strain rate is 0.1s-1, strain at 0.6. By this, the average grainsize is 5μm, which is suitable for stamping. It is found that there is originalbig grain in the structure of sheet not pre-treated, and the pre-treatment ishelpful to the rolling process. Based on the strain-stress curves, the flowstress model is gained using liner fit method, which can be used as thefundamental data for the further researching of the deforming of continualcasting and rolling magnesium alloy sheet.Magnesium alloy sheet produced with CCR process and hot rolling canreduce the process to produce thin sheet, and the data can be referred inmanufacture. |
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