| Magnesium alloys are characterized by low density,high strength,high stiffness,vibration damping and electromagnetic shielding.They are widely used in various fields where lightweight structures are required,such as the automotive industry,aerospace,weaponry and electronic products.However,the high chemical reactivity and poor corrosion resistance greatly limit the use of magnesium alloys.Therefore,protective treatments are often required to improve the suitability of magnesium alloy materials in different environments.When magnesium and its alloys are exposed to the atmosphere,magnesium rapidly forms porous,poorly bonded,non-uniform oxide,hydroxide and carbonate films that do not provide satisfactory corrosion protection.Therefore,magnesium alloys must be surface modified and surface coated,which is an effective means of protecting the base material from the environment to improve corrosion resistance.The surface treatment of the magnesium alloy by electroless plating can form a coating on the surface of the magnesium alloy which is resistant to abrasion,corrosion and uniform thickness,and is widely used in many fields.However,the current application of magnesium alloy electroless nickel plating technology will produce a large amount of environmentally harmful Cr6+,which will cause threats and damage to the human body and the environment.Therefore,this paper explores the effects of changing variables on the direct electroless nickel plating process of magnesium alloys and the pre-treatment process of green environmental protection.This subject uses the control variable method to prepare Ni-P coating on the surface of magnesium alloy substrate.The effects of different factors on the properties of the coating were investigated by changing the plating time,plating temperature,plating pH value,heat treatment temperature,magnetic field strength,magnetic field method and pretreatment process.The obtained magnesium alloy nickel-pHospHorus coating was characterized,the surface morpHology of the coating was measured by optical microscope,the bonding force of the obtained coating was measured by an automatic scratch tester,and the wear resistance of the magnesium alloy coating was obtained by using a friction and wear tester.The hardness of the coating is tested using a microhardness tester to analyze the test results,and then to study the mechanism of the influence of different factors on the electroless plating process and to obtain a green pre-treatment process.Through research and analysis,we can get:?1?The binding force of magnesium alloy nickel-pHospHorus plating increases with a certain temperature within a certain range.The optimum temperature is 80?.The temperature has a certain influence on the wear resistance,and the specific performance is that the wear resistance increases as the temperature increases.The heat treatment process can significantly increase the hardness of the coating,heat treatment can increase the wear resistance,the coating is heat treated,and the coating properties and structure will change.?2?The applied magnetic field during plating can affect the deposition rate of ions in the coating.The addition of alternating magnetic field and static magnetic field will affect the hardness of the coating.When the strength of the alternating magnetic field is increased,the hardness of the magnesium alloy nickel-pHospHorus coating increases first.After the trend of reduction.?3?The addition of alternating magnetic field and static magnetic field can affect the wear resistance of magnesium alloy nickel-pHospHorus coating to a certain extent.Under alternating magnetic field,the wear resistance of the coating is best when the AC voltage is 24V,and the static magnetic field strength is Below 6mT,the wear resistance of the coating is affected by the magnetic field,and the wear resistance is enhanced with the increase of the magnetic field.The bonding force between the magnesium alloy plating layer and the substrate increases as the strength of the static magnetic field increases.?4?By changing the pre-treatment,under the conditions of no chromic acid etching and HF-free activation,while avoiding the use of environmentally harmful chromic acid and hydrofluoric acid,it is found that the magnesium alloy can be uniformly formed by exploring the coating properties.Compact Ni-P coating,so the use of lanthanum nitrate,lanthanum nitrate,potassium permanganate pretreatment can be used as a green alternative to hexavalent chromium and hydrofluoric acid. |
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