Wettability And Salt Spray Corrosion Resistance Of Magnesium Alloys Treated With Laser Surface Texturing

With a series of advantages such as high specific strength,good specific stiffness,good machinability and castability,and recyclability,magnesium alloys are considered to be the most promising green engineering material of the 21 st century.However,the extremely low electrode potential of magnesium alloys and their susceptibility to corrosion in humid environments have limited their development,so it is vital to improve the corrosion resistance of magnesium alloys.In this paper,laser processing is used to regulate the surface wettability state of magnesium alloy,and the laser processing process and the influence law of the surface wettability state of magnesium alloy on the corrosion resistance to salt spray are studied,and the related mechanism is revealed.The main research contents and conclusions are as follows:(1)Laser surface texturing to regulate the surface wettability of AZ91 D magnesium alloy.Different laser parameters were used to build a rough texturing on the surface of magnesium alloy,and then combined with low temperature heat treatment to achieve the wettability control of magnesium alloy surface.The influence of the process parameters on the surface of magnesium alloy was investigated.The results show that laser power,laser scan speed and scan spacing have an important influence on the surface morphology and wettability of the magnesium alloy.The hydrophobicity of the periodically texturing surface is better than that of the randomly texturing surface;micro-nanoparticles generated during laser processing are attached around the surface texturing,forming a multi-level structure,which is conducive to the construction of a superhydrophobic surface.(2)Mechanistic study on the change of surface wettability of AZ91 D magnesium alloy.After laser processing,the surface of AZ91 D magnesium alloy shows super hydrophilic state,and the contact angle will change significantly after low temperature heat treatment.The influence law of elemental composition etc.on the surface wettability of AZ91 D magnesium alloy was studied.The results show that the elemental C content of the AZ91 D magnesium alloy surface increases significantly after heat treatment.The adsorption of organic C molecules in the air on the surface of the substrate reduces the chemical free energy on the surface of the magnesium alloy,which results in a change in the wettability of the magnesium alloy.(3)Study of the salt spray corrosion resistance of AZ91 D magnesium alloy with different wettability states.The corrosion behaviour of AZ91 D magnesium alloy was investigated by characterising the corrosion degree and the thickness of the corrosion layer of untreated,hydrophilic,hydrophobic and superhydrophobic specimens.The results show that the untreated,hydrophilic and hydrophobic specimens all corrode severely,while the superhydrophobic specimens show good corrosion resistance.Laser treatment can induce the formation of oxide film on the surface of magnesium alloy,in the early stage of salt spray corrosion the oxide film plays a protective role for the substrate,slowing down the corrosion rate;with the extension of corrosion time,the oxide layer is gradually destroyed and loses its protective effect.The superhydrophobic surface obtained by laser treatment improves the corrosion resistance for the following reasons: the superhydrophobic surface greatly reduces the contact time between the corrosive medium and the surface of the substrate,and the presence of a protective oxide film on the surface of the specimen,both of which synergistically improve the corrosion resistance of AZ91 D magnesium alloy effectively.