Study On Corrosion Resistance Of AZ80 Magnesium Alloy Tubes By Hydrostatic Extrusion

Hydrostatic extrusion technology solved the difficult problems of plastic deformation processing of magnesium alloy under normal temperature. Magnesium alloy tubes with excellent mechanical properties can be gotten through it. But in practical application, the corrosive characteristic of magnesium alloy was the key to restrict its widespread application.The effects of hydrostatic extrusion process on AZ80 magnesium alloy corrosion behavior and the influence of heat treatment on the corrosion behavior of hydrostatic extrusion tubes were studied, in the case of as-cast, hydrostatic extruded,350℃1h,350℃2h and 350℃4h. The microstructure was studied by optical microscope, the expansive process of the corrosion was recorded by digital camera, the corrosion micro-morphologies were observed by scanning electronic microscope and the corrosion products were studied by X-ray diffraction. The corrosion rates were investigated with weight loss method, the corrosion current densities were calculated with Tafel lines according to the polarization curves and the impedance fitting parameters were simulated with equivalent circuit according to the electrochemical impedance spectroscopy.Some results were concluded:(1) The hydrostatic extrusion produced large numbers of sub-grains and dislocation tangles within AZ80 magnesium alloy. The corrosion resistance of hydrostatic extruded AZ80 magnesium alloy was lower than as-cast, with more serious corrosion morphology, with bigger average corrosion rate, with larger corrosion current density and lower corrosion resistance. (2) The re-crystallization of hydrostatic extruded AZ80 magnesium alloy occurred during annealing. That could effectively improve the corrosion performance of magnesium alloy for changing microstructure and composition distribution and reducing the dislocation density. Appropriate heat treatment could improve the corrosion resistance of hydrostatic extruded AZ80 magnesium alloy. In addition, the time of heat treatment would affect the corrosion resistance of alloy. With the heat treatment time extended, the corrosion resistance of hydrostatic extruded AZ80 magnesium alloy could be reduced. The results of this dissertation had reference value in the process of thermal-rheological forming and the exploitation of high-performance complex structural components for magnesium alloy.