An experimental investigation was performed into the formability of magnesium alloy
sheets that were hot-rolled after a semi-solid roll strip casting process. Semi-solid forming helps reduce the total product weight if the semi-solid material produced by light metals, such as aluminum and magnesium can be used to replace conventional iron and steel products. However, the problems of utilizing magnesium alloys are still related to high manufacturing costs. This means that improved quality must be balanced by economic validity. Magnesium alloy AZ31B was used in this experiment to ascertain the effectiveness of semi-solid roll strip casting for producing magnesium alloy sheets. The temperature of the molten magnesium, and the roll speeds of the upper and lower rolls, (which could be changed independently), were varied to find an appropriate manufacturing condition. Rolling conditions and heat treatment were changed to examine which condition would be appropriate for producing wrought magnesium alloys with good formability. Microscopic observation of the crystals of the finished products was performed. It has been found that a limiting drawing ratio of 2.4 was possible in a deep drawing process of the cast magnesium alloy sheets.
Authors addressed the case of bending using a press brake, and experimentally investigated and evaluated the effects of various conditions on the bending limit and bending accuracy for an AZ31 magnesium Mg alloy sheet thickness tϭ0.5 mm in air bending. The results indicate that cracks were generated on the surface of the Mg alloy sheet when the bending punch radius was smaller than 1.5 mm three times of the sheet thickness . To prevent these cracks, warm bending was required, in which the sheet material was heated to 250°C. Also, the amount of springback of Mg was larger than steel when bending at room temperature, since the modulus of elasticity of Mg is smaller than that of steel. However, when the bending temperature was high, the amount of elastic recovery of Mg rapidly decreased, resulted in a significant decrease in springback. When the bending temperature was as high as approximately 300°C, bent products with nearzero springback were obtained. In addition, we quantitatively determined the effect of various bending conditions, such as bending punch radius, die opening and bending temperature, on the bend radius and bend allowance of products. The results provide useful data that can serve as guidelines in actual bending process.
In previous studies, it is known that forming products with practical depth made of AZ31 magnesium alloy sheets can be obtained by applying the warm-deep drawing, where a heated die, blank holder and water-cooled punch are used. However, in‰uence of tool radius, which is one of signiˆcant factors on deep drawing formability, has not been examined systematically under the practical forming speed condition in which hydraulic or mechanical press machine forming are assumed. In this study, we systematically examined eŠects of tool radius and forming speed on the forming limit of warm-deep drawing for the cylinder and square cups. Furthermore, we studied the possibility of the reform of a square cup with small shoulder and corner radii by sizing, as it is di‹cult to form by only deep drawing.
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