Research On Plastic Processing Technology And Corrosion Of Thin Tube Of AZ31magnesium Alloy

Magnesium alloy is an ideal cardiovascular stents biomedical material because of its good biomechanical compatibility and degradable characteristics as well as mechanical properties. This paper researched a new extrusion technology to manufacture magnesium alloy thin-walled tube with large slenderness ratio and high strength as well as high toughness at low temperature with the help of a force transmission lubrication medium. This technology also revealed the mechanism and law,at the same time, of low-temperature extrusion plastic deformation, realizing integrated control for the micro-structure and properties of magnesium alloy and precision forming.This also produce important significance for the application of magnesium alloy thin-walled tube with high strength and high toughness in the field of biomedicine.In this paper, cast AZ31 magnesium alloy bar stock which was raw materials was tested adopting the hollow spindle forward extrusion approach. The technology parameters of extrusion forming were conformed and the best parameters were optimized according to the laboratory condition. The paper researched uniformity of tube wall thickness by hollow ingot positive extrusion and the influence of microstructure and properties of AZ31 magnesium alloys in different heat treatment time and temperature. Simulating body fluid corrosion was done later to test the corrosion rate and production.Studies showed that the segregation and inhomogeneous of cast AZ31 magnesium alloys after heat treatment declined, and the second phase melt into the gr ain from bounty, the twins reduced.The Φ3.0mm tubes were gained after two steps of extrusion deformation. Due to large plastic deformation, the analysis showed the dynamic recrystallization happened and grain size was refined to 8.4μm and tensile strength is 223.5MPa as well as the elongation is 9.5% with ductile fracture. Above all, micro-structure and properties were improved compered to the cast.In the process of heat treatment, when the temperature got 225℃, grain size was refined, tensile strength retained 257.5MPa with high elongation; when the remained 45 minutes, the tubes got high mechanical properties such as 7.5% elongation during to refined grain about 5.1μm with ductile fracture type.A lot twins showed along with the increasing of deformation when drew fro m Φ3.0mm to Φ2.5mm, the elongation declined from 9.5% to 7.3% while the te nsile strength improved from 223.5MPa to 240.3MPa; when drew from Φ2.5mm to Φ2.0mm, the elongation was 7.0% while tensile strength was 256.3MPa.The corrosion types were mainly in the grain and along the bounty corrosion. The grain size and structure are related to corrosion rate in simulating body fluid corrosion,the corrosion rate increasing with the refined grains and the decreasing twins. The maximum corrosion rate was 28.5mg/(cm2·day) and the minimum corrosion rate was9.3mg/(cm2·day). The product of body fluid corrosion is Mg(OH)2 as well as few Mg H2.