The influence of the parameters of hot drawing of MgCa alloys wires on the mechanical properties that determine the applicability of the material as a high strength biodegradable surgical thread

摘要

Magnesium alloys with calcium are some of the promising materials for creating soluble surgical threads. The recommended daily intake of magnesium in the human body is 375-500 mg, calcium - 800 mg. Other candidates as a material for surgical sutures are zinc and iron. For them, this parameter is 6.5-11 mg and 6-20 mg, respectively. Thus, in terms of the permissible content in the body, magnesium-calcium alloys compare favorably with other materials. However, these alloys have low ductility in the cold state and low deformability during drawing. The paper proposes to obtain wire from MgCa0.7, MgCa0.9 alloys by hot drawing. Moreover, the drawing process consists of deformation of the metal in the heated die and recrystallization during the movement of the workpiece. These processes allow us to control the microstructure of the finished wire to obtain the necessary ductility. The theoretical part of the work was to develop a mathematical model of the hot drawing process, taking into account the dependence of the flow stress on deformation, temperature, and strain rate, as well as recrystallization processes. To calibrate the model of flow stresses, experiments in the GLEEBLE machine were carried out to compress the sample under various thermomechanical conditions. To calibrate the recrystallization model, the initial compression of the sample to a strain of 0.1-0.3 and the subsequent registration of stress relaxation was carried out. The resulting material models were implemented in the FEM model of hot drawing. It made it possible to calculate the range of permissible parameters of the drawing and determine the optimal values of the speed and temperature of the drawing. The experimental part of the work consisted of a three-pass wire drawing with an initial diameter of 1.8 mm to a final diameter of 1.5 mm at various temperatures: 350°C, 400°C and 440°C. After the drawing was completed, the microstructure and mechanical properties of the wire were analyzed. The maximum elongation of the wire was observed for the maximum temperature (440°C) and amounted to 20% with Tensile Strength (TS) 230 MPa, which is sufficient to use the material as a thread. An in vitro corrosion tests showed that an increase in the temperature of deformation and annealing leads to accelerated corrosion. Thus, the data obtained allowed us to find a compromise between the strength, ductility, and corrosion rate of a MgCa magnesium alloys wire.