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Experimental study of nickel magnesium alloy plating ZM6

Author: GaoYanRui
Tutor: LiuChuMing
School: Central South University
Course: Materials Processing Engineering
Keywords: ZM6 magnesium alloy electroless nickel plating acid pickling zinc immersion corrosion resistance
CLC: TG174.44
Type: Master's thesis
Year: 2011
Downloads: 93
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Abstract


To improve the corrosion resistance of ZM6 magnesium alloy, two electroless nickel plating processes on ZM6 alloy with new pretreatment process were investigated in this paper. The morphology, component, chemical composition and structure of the pretreatment layers and electroless nickel coating were analyzed by scanning electronic microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction spectroscopy. The adhesion and corrosion resistance of the Ni-P coating were evaluated by means of thermal shock, potentiodynamic polarization, and salt spray tests. Experiment results are obtained as follows.1) The electroless nickel plating process:degrease→acid pickling→zinc immersion→nickel plating is improved by new acid pickling solution. And the suitable compositon of acid pickling solution for ZM6 alloy is as follows:CrO310 g/L+HNO310 ml/L. The acid pickling layer did not participant in zinc immersion reactions, and could assist to produce the compact zinc film with good adhesion.2) The properties of nickel coating are as follows:Its thickness reached about 62μm at 2 h deposition, and the deposition rate was nearly three times of traditional electroless nickel plating; it was uniform and amorphous, in which the content of P was 9.7 wt.%; compared with the bare substrate, the corrosion potential of the coated alloy shifted by 1075 mV positively and the corrosion current density decreased two orders of magnitude in 3.5 wt.% NaCl solution; the salt spray test time of Ni-P coating was 158 h;the coating-substrate adhesion was more than 12MPa; it lowered the tensile strength and yield strength by 12% and 5% repectively; it owned good anti-humid property and the anti-fungi propertity reached level one.3) In concern of the environment and simplification, the electroless nickel plating process:degrease→zinc immersion→nickel plating is improved by new zinc immersion solution. A compact, well- distributed zinc coating is obtained on the surface of ZM6 alloy in a new zinc immersion solution with addition of Sn+.4) The subsequent amorphous electroless nickel coating obtained by process(degrease→zinc immersion→nickel plating) is uniform and the thickness is 8.7μm after 1 h deposition with 9.3 wt.% P. The corrosion potential of the coated alloy shifted by 781 mV positively and the corrosion current density decreased one order of magnitude in 3.5 wt.% NaCl solution.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology > Metal complex layer of protection
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