Effect of extrusion combined with ECAP and ultrasound on the structure and properties of an Mg-Zn-Zr alloy

Development of implant systems from bioresorbable metals and alloys within the framework of modern osteosynthesis techniques is one of the priority and actively developing areas of medical materials science. Among the materials suitable for this role, the Mg-Zn-Zr magnesium alloy system stands out, characterized by good biocompatibility, strength, and an elastic modulus value close to that of human bone. However, for this specific application, the corrosion behavior of these magnesium alloys requires improvement. In the present study, using the Mg-5.8Zn-0.5Zr alloy as an example, a novel combined method of thermomechanical processing was applied, which is distinguished by the simultaneous application of ultrasonic waves to the workpiece during the process of equal-channel angular pressing combined with extrusion (EX-ECAP-US). A distinctive feature of the proposed method is the ability to produce long-length semi-finished products in the form of rods. The influence of different temperatures (400 and 300°C) at a deformation speed of 5.6 mm / s, as well as the simultaneous ultrasonic treatment with an oscillation amplitude of 5 μm and a frequency of 20 kHz, on the structural characteristics and properties of the processed samples was investigated. It is shown that at all considered deformation temperatures, the ultrasonic treatment applied during the EX-ECAP process leads to a decrease in the average grain size. XRD analysis established that the application of ultrasound during the EX-ECAP process leads to a reduction in microstrains and dislocation density compared to processing without ultrasonic treatment. The samples obtained at a temperature of 400°C with the application of ultrasound exhibit the most balanced set of mechanical properties. Moreover, all considered states after EX-ECAP-US are characterized by a high elongation value, reaching 23 %. Electrochemical corrosion resistance tests in Ringer’s solution indicate resistance of approximately the same order of magnitude for states subjected to EX-ECAP both with and without ultrasound.

1. Russian Science Foundation - 22-79-10325П