| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2001: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2000: ¥2,700,000 (Direct Cost: ¥2,700,000)
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| Research Abstract |
The most popular grain refiner consisting of C_2 CI_6 was used in industry for grain refining of magnesium alloy containing an aluminum element. However, it has a great problem, because it generate the dyoxine matter by the decomposition of chloride. At present, it cannot use at all. On the other hand, it is well known that the superheat treatment is effective for grain refining of Mg-AI system alloys, however, the grain refining mechanism is not clarified yet. The advantage of this method keeps clean the environment, because harmful grain refiners such as C_2 CI_6 were not used so that it is useful technology, except the larger thermal energy is consumed because of the high temperature.
The purpose of this investigation is to clarify the grain refining mechanisms of the superheat-treated AZ 91 magnesium alloy. The molten alloys were quenched at various temperatures and cast into the mold after superheat treatment. Each sample reveals each high temperature state as quenched. Each sample is examined by an optical microscope and EPMA. The primary magnesium dendrites were generated from the heterogeneous nuclei of AI_4 C_3. The impurity elements in the magnesium alloy such as Mn, Fe, Si, and Cu were melted in the molten magnesium alloy, however, C was remained in the superheat treated molten alloy. In this process, C and AI reacted and formed AI_4 C_3. High purity Mg-AI alloy was also cast with and without superheat treatment. Both samples were refined for the grains because the AI_4 C_3 compounds were able to form easily without the superheat treatment. It is concluded that the AI_4 C_3 compounds in the commercial AZ91 alloy were formed during the superheat-treatment and they nucleated the primary crystals of magnesium.
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