Electroless Nickel-Phosphorus Plating Process Of Magnesium-Lithium Alloy

The electroless nickel-phosphorus alloy plating of magnesium-lithium alloy has the better characteristics of uniform coating,good conductivity and corrosion resistance,so it has great research value in the surface treatment of magnesium-lithium alloy.Due to the extremely strong activity of magnesium-lithium alloys,how to increase the bond strength of the Ni-P alloy layer has become a difficult point.The paper first obtains the excellent pretreatment process for magnesium-lithium alloy by optimizing the pretreatment process of electroless nickel-phosphorus alloy of magnesium-lithium alloy.Then the alkaline electroless nickel-phosphorus alloy process was studied to improve the combination of nickel-phosphorus alloy layers force.In this paper,the single factor test was performed on the pickling process,in order to study the effect of nitric acid,phosphoric acid,glycerin and pickling time on the performance of the Ni-P alloy plating,and finally the best pickling process was obtained.Besides that,the single factor test was also performed on the activation process.The purpose is to study the effect of ammonium hydrogen fluoride,phosphoric acid and activation time on the properties of Ni-P alloy layer,and finally the best activation process was obtained,so that the subsequently Ni-P alloy plating was firmly bonded to the matrix.In the paper,firstly the zincation components and process parameters were separately subjected to orthogonal test.The results show that the concentration of potassium pyrophosphate and the temperature of zinc leaching are the main factors determining the performance of Ni-P alloy layer.Secondly,the single factor test was performed on the zincation process,and the microstructure of the zinc-immersed layer was analyzed by scanning electron microscopy(SEM).The results show that after the secondary zinc-immersion,the zinc layer is more firmly bonded to the substrate and the coverage is uniform.Through the single factor test,the zinc removal process is optimized,and we can obtain effective zinc removal process,removing the zinc layer that is not bound to the substrate and reducing the corrosion of the substrate.In this paper,we performed orthogonal tests on the components of alkaline electroless nickel-phosphorus alloy solutions.The results show that the concentration of complexing agent A is the main factor that determines the performance of Ni-P alloy layer,while the effect of Ammonium hydrogen fluoride concentration is less.The alkaline electroless nickel-phosphorus alloy process suitable for Mg-Li alloys is selected.The Ni-P alloy layer firmly bonded to the substrate is deposited on the surface of the substrate to provide more nucleation sites for electroless nickel-phosphorus alloy plating.The resulting electroless nickel-phosphorus alloy layer can be subjected to a thermal shock test and cross-cut test at 250°C.The paper used time-potential curves,SEM and EDX to study the growth process of alkaline electroless nickel-phosphorus alloys.The results show that alkaline electroless nickel-phosphorus alloys are mainly divided into three stages.In the first stage,the zinc layer in the surface of the substrate reacts with the soluti on to expose part of the substrate.The second stage is the displacement reaction between nickel ions in the magnesium matrix and magnesium matrix or zinc layer.The third stage is the co-deposition reaction of Ni-P alloy on the surface of the substrate.This paper analyzes the economic cost of the whole process of electroless nickel-phosphorus alloy plating.The cost of the electroless nickel-phosphorus alloy plating is low and it is expected to be applied in the surface treatment process of Mg-Li alloy.