| Magnesium alloy owns many excellent properties such as biocompatibility,degradable and mechanical properties. In the modern medical equipment applicationfield, magnesium alloy has great superiority. This paper studies a new capillaryextrusion technology that is magnesium alloy low temperature extrusion. Thistechnology reveals the plastic deformation mechanism of low temperature andresearches the deformation laws systematically. Lay the foundations for the theories andtechnologies on the plastic processing application of magnesium alloy thin tube.Develop a new material for magnesium alloy capillary. The material has high dimensionaccuracy, strength and toughness. It can realize integrated control for the organizationand property of magnesium alloy and precision forming. It has important meanings forexpanding application field of magnesium alloy which has tiny size, high strength andtoughness. Finally we can obtain a new manufacture technology of tiny tubes.This paper studied on AZ31magnesium alloy and used a forming technology ofhollow ingot positive extrusion. The studies of extrusion experiments were relativelysystematical. Got the technology parameters of extrusion forming and optimized theprocess parameters continuously through experiments. Realized thin tubes extrusionforming of AZ31magnesium alloy. This paper analyzed the experiment results throughthe equipments of metallographic microscope, electronic universal test machine andVickers micro-hardness gauge. And analyzed uniformity of tube wall thickness whichmade by hollow ingot positive extrusion. It also studied that heat treatment time anddifferent extrusion parameters such as extrusion temperatures and the ratio of extrusionhow to influence AZ31magnesium alloy grain sizes and the properties.The results showed that: tube wall thickness was relatively uniform when extrudedby hollow ingot positive extrusion with the defined process parameters. The ratio ofwall margin reduced gradually from the head to the end. The minimum of the ratio ofwall margin is2.5%. The surface of tubes didn’t have defects of cracks, layers anddepressions. The roughness of the surface and the precision of the dimension are quitegood.The dynamic recrystallization happened and grain size was refined at the firstextrusion process, but dynamic recrystallization happened incompletely. The dynamicrecrystallization completely happened at the second extrusion process and grain sizeuniform, but grain size grew up slightly.Along with the rise of blank temperature, the grain size increased graduallyreduced, strength and hardness reduced gradually. The results showed that under theconditions of mould preheating temperature at300℃, the first blank temperature at200 ℃and the second blank temperature at150℃, tubes of Φ8mm×1mm could obtainoptimal comprehensive properties. Along with the rise of extrusion ratio, the effect offine-grain strengthening was more obvious. Not only grain sizes gradually reduced butalso comprehensive properties gradually increased. The results also showed that tubeswhose outside diameter less than or equal to4.1mm and extrusion ratio is31.5couldobtain optimal comprehensive properties.The static recrystallization occurred in the heat treatment process, grain sizes wereuniform relatively. Along with the extension of the annealing heat preservation time, notonly grain sizes grew up, but also the compressive strength and the hardness of tubesgradually reduced. Especially, grain sizes grew up abnormally and the compressivestrength and hardness greatly reduced when the annealing heat preservation time was120min. Along with the annealing temperature increased, grains almost not grew up andso the compressive strength and the hardness of tubes. The tubes achieved betterproperties when holding temperature30min at225℃. |
