Drawing of magnesium fine wire and medical application of drawn wire
Natthiwan Dodyim, Kazunari Yoshida, Tomoaki Murata, Yusuke Kobayashi
Abstract
Magnesium is not only classified as one of the lightweight materials, but also expected to be applied in medical stents and medical artificial joint screws because of its good biocompatibility and biodegradability in the human body. Our research has studied the production of sound pure magnesium fine wire for the medical stent by the cold drawing method. Pure magnesium wires are known to have low ductility and poor formability at room temperature. It is pointed out that its crystal structure has a close-packed hexagonal crystal and hence the slip surface during deformation is limited. Therefore, the cold drawing of magnesium wire is very difficult. In this research, the finite element analysis (FEA) and Cockroft-Latham fracture criterion have been conducted to clarify the optimum drawing conditions for obtaining a fine wire without an internal crack by studying the relation between the die half angle and the pass reduction that affects the drawability of pure magnesium wire. The results show that 6o of die half angle and 13 % of pass reduction are suitable conditions to prevent an internal crack. Furthermore, the intermediate annealing process was also examined to prevent the generation of small voids in the center of the wire. Consequently, we succeeded to draw the fine wires with 0.5 mm in diameter without internal cracks and good finishing surface roughness.