Effect Of Extrusion Ratio On The Microstructure And Properties Of Mg-Sn Alloy

Magnesium-based material, a new biodegradable medical material, could be applied as cardiovascular stents, bone fixation implant or the bone filler. As an implanted device in the treatment of cardiovascular diseases, magnesium alloy stent is expected to provide enough mechanical support in early stages and be able to degrade and be absorbed by organisms after the healing of the vessels.Magnesium alloys are mainly fabricated by pressure casting while there is seldom pressure processing ones, which accordingly limits the application of magnesium alloys in medical device industry. Hot extrusion forming technology, as one of the best solid forming processes, has been the focus of the research due to its many advantages. Extrusion technology could bring higher three-dimension compressive stress state to magnesium alloy than rolling could do, and to the greatest extent, improve the plasticity of the magnesium alloy which usually has a poor plasticity.The present work focused on the extrusion molding process of magnesium alloy bars. Three biomedical magnesium alloys, namely, Mg-3Sn-0.5Mn, Mg-3Sn-1Zn and Mg-3Sn-1Zn-5Mn, have been produced by extrusion molding in this work with three different sets of extrusion processing parameters. The effect of extrusion ratio on the microstructure, phase composition, mechanical properties, electrochemical corrosion properties and biocompatibility of the three magnesium alloys has been studied.The results have shown that Mg-3Sn-0.5Mn, Mg-3Sn-1Zn and Mg-3Sn-1Za-0.5Mn alloys which go through the extrusion process with the extrusion temperature 370℃, extrusion speed 1.5m/min, graphite lubrication and extrusion ratio of 6,13 or 20 could achieve improved tensile strength above 200MPa with elongation rate dropping slightly, owing to their obviously refined crystalline grain compared with that of as-cast magnesium alloys. Moreover, the corrosion rate of the alloys produced by extrusion changes little, compared with that of the as-cast ones. However, hemolysis ratio decreases with the increase of the extrusion ratio from 6 to 20 and the minimum hemolysis ratio (2.9%) could be obtained for the alloys with extrusion ratio 20.The elongation rates of Mg-3Sn-0.5Mn and Mg-3Sn-1Zn alloys are 16.3% and 16.8%, respectively, after extrusion with extrusion ratio 6, which allow multi-pass extrusion for these two alloys; while the use of extrusion ratio 20 would lead to large deformation, which requires a decrease of the number of extrusion process. The elongation rate of Mg-3Sn-1Zn-0.5Mn alloy after extrusion with extrusion ratio 6 is 18.7%, which supports multi-pass extrusion for this alloy.