Electroless Ni-P/Ni-Cu-P Coatings On AZ91D Magnesium

Mg distributes very broadly in the nature, and arranges in thirdthat is only inferior in Al and Fe, it is one of the richest elements inthe earth's crust. Mg alloy is one kind light quality alloy material thatcan meet each industry need, and it's developing foreground isextremely considerable. because of the high specific tenacity, thegood anti-impact performance, Mg alloy can satisfy the need ofaviation, astronautics, automobile and electronic products.But thechemical activity of Mg is high, the standard electrode potential is-2.37V(relative to the standard hydrogen electrode). In the dryatmosphere, the surface of Mg can form the thin film of oxidecompound that has the certain protective function to the substrate. Butthe compact coefficient of the nature producted oxide film is 0.79, Itis smaller than 1, In other words, after Mg is oxidized, the volume ofthe oxide compound reduces, the oxide film is loose and porous.Therefore, the corrosion resistance of Mg and Mg alloy is quite bad,and Mg and Mg alloy take on the very high chemical andelectrochemical activity, all of them limite the application of Mgalloy.Along with the thorough research and widespread application ofchemistry Ni plating craft and coating organizational structure andperformance, some main characteristics of chemistry Ni platingreveal gradually, that establishes the status that could not besubstituted of chemistry Ni plating in the surface plating domain. Thispaper chooses to carry on the chemical plating in the surface of Mgalloy, that can improve the corrosion resistance, the physicalperformance and the mechanical performance, and achieve the goalthat expand the application of Mg alloy.This paper takes Mg alloy as research object in experimentalstudy period, it has prepared double-decked Ni-P/Ni-Cu-P alloycoating in the surface of Mg alloy successfully, At the same time, italso has prepared Ni-P binary alloy coating for the comparison.The paper mainly includes the following contents:(1)This paper has studied the chemical plating principle andcraft of chemistry Ni-P/Ni-Cu-P plating of Mg alloy, and has findedout suitably plating condition, and has determined the chemicalplating formula.(2)Carried on the test using EDS and XRD to the differentcoating ingredient and the organizational structure. The findingsindicated, changed the parameter of plating craft can obtain theNi-Cu-P coating of the different P,Cu content, the chemical platingcraft which we choose to obtain for indefinite crystalless conditioncoating, all of them guaranteed in the organizational structure thatcoating has the good corrosion resistance.(3)Observes and analyzes the superficial appearance of Ni-Pcoating and Ni-Cu-P coating using the scanning electron microscope.The findings indicated, The Ni-Cu-P ternary alloy coating superficialappearance and the Ni-P binary alloy coating superficial appearanceis similar, The surface is the butcher shape structure, that cover insubstrate compactly, and there isn't obvious hole on it.(4)Test the polarization curve of the substrate and the differentcoating. The findings indicated, the corrosion electric potential of theNi-Cu-P coating is about -0.58V, compared to Ni-P, it has theenhancement slightly, Theoretically, it had guaranted Ni-Cu-Pcoating that has the good corrosion resistance. In addition, tested thecorrosion resistance of the coating using 10%HCl. The findingsindicated, The test specimen don't to corrode continues 200 minutesin 10%HCl, Degree of hardness may reach 576HKV, and the coatingbinding force is good, it has good preventment to Mg alloy.