The use of biodegradable magnesium alloys for implants in osteosynthesis involves the manufacture of complex shape structures with a variety of holes, threads, etc. In this regard, there is a need to use a material with an increased complex of mechanical properties to ensure the good quality of manufactured complex elements

One way to improve the microstructure and increase the mechanical properties of the alloy is to provide the required cooling rate of casting, which is achieved by the use of various mold materials and coolants.

The simulation of the casting process with the different cooling rates and their effect on the structural parameters of the magnesium alloy were performed using ProCast^TM software. The calculations were performed for the following technologies: sand casting; casting in a steel mold, air cooled; casting in a copper mold, air cooled; casting in a copper mold, water cooled; casting in a copper mold, cooling with liquid nitrogen.

Casting in a metal mold is more effective than sand casting because, due to the higher cooling rate, it provides better microstructure parameters of the alloy. The secondary dendrite arm spacing (SDAS) has been reduced by almost 2 times, the spread in the values by volume also decreased. The difference was higher with increasing the cooling rate when casting in a metal mold.

Increasing the cooling rate resulted in significant grain refinement as well as a decrease in grain size deviation from the mean. So, the use of a copper mold with water cooling leads to grain refinement of the alloy by almost 2 times compared to sand casting.

Practical studies of the microstructure and mechanical properties of standard cast samples confirm the calculations made using ProCast^TM software. The average grain diameter of the matrix for sand casting was 177 μm, for casting in a steel mold with air cooling - 88 μm, for casting in a copper mold with air cooling - 60 μm, for casting in a copper mold with water cooling - 31 μm, for casting in a copper mold with cooling with liquid nitrogen - 11 microns.

As a result, the improvement of the microstructure parameters of the Mg-Zr-Nd magnesium alloy has led to the improvement of the complex of mechanical properties of the alloy after heat treatment (Table 1).

Table 1 - Mechanical properties of Mg-Zr-Nd magnesium alloy at different cooling rates