Az31 Magnesium Alloy Electroless Ni-p Amorphous Plating And Its Crystallization

Magnesium alloys are the lightest metal structure materials in the practical application. They have been widely used in aerospace, automobile and electronics industry for its outstanding characteristics, such as high strengh-to-weight ratio, high electromagnetic shieldlessness, good dampness, good damping property and machinability, etc. However, the chemical properties of magnesium alloys are very active, poor corrosion resistance has often prevented it from further exploitation. Before used magnesium alloy workpiece must be protected by certain surface treatment processes, Electroless plating on the surface of Magnesium alloys is an effective method. Ni-P coating with high corrosion resistance and wear resistance can be obtained on magnesium alloys and uniform coating can be gained especially on complex castings.This article mainly focused on electroless plating on AZ31 magnesium alloy. Electroless Ni-P plating obtained on AZ31 magnesium alloy is smooth and bright, and has a high adhesion strength. Then of pretreatment process before electroless has been optimized. The effects of some factors including main salt, reducing agent, pH and temperature to electroless rate are studied. The deposit coating morphology, microstructure, composition and crystallization temperature are determained and analysed by using OM and SEM observation, EDS analysis, XRD analysis, DSC analysis. Finally, the properties of electroless plating before and after heat treated has been studied by salt spray exposure and electrokinetic potential polarization curve research techniques.The hardness of electroless Ni-P plating is about decuple as the bare alloy. High hardness could extend its using life. The electroless Ni-P plating has high corrosion resistance in the 3.5% sodium chloride solution. The corrosion potential of electroless Ni-P plating shifts about 800mV to the positive potential direction than the corrosion potential of the bare alloy, and no peeling occurs on surface of the plated sample until 72 hours lasted. It shows that the corrosion resistance of the plated sample improvs a lot. After the crystallization at annealing condition, the hardness of electroless Ni-P plating further improves, but the corrosion resistance drops with the plated sample before the crystallization.