Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming nonmetal coating
Patent
1991-07-15
1993-11-23
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming nonmetal coating
205219, C25D 1130
Patent
active
052641139
ABSTRACT:
A two-step process for the coating of magnesium and its alloys is disclosed. The first step comprises immersing the magnesium workpiece in a first electrochemical solution comprising about 3 to 10 wt-% of a hydroxide and about 5 to 30 wt-% of a fluoride having a pH of at least about 12. By controlling a current density to about 10 to 200 mA/cm.sup.2, an increasing voltage differential is established between an anode comprising the pretreated article and a cathode also in contact with the electrolytic solution. Next, the article is immersed in an aqueous electrolytic solution having a pH of at least about 11 and which solution is prepared from components comprising a water soluble hydroxide, a water soluble fluoride source and a water soluble silicate in amounts to result in an addition of about 2 to 15 g of a hydroxide per liter of solution, about 2 to 14 g of a fluoride per liter of solution and about 5 to 40 g of a silicate per liter of solution. Again, by controlling the current density to about 5 to 100 mA/cm.sup.2, an increasing voltage differential of at least about 150 volts is established between an anode comprising the pretreated article and a cathode also in contact with the electrolytic solution. This process results in a superior coating which has increased abrasion and corrosion resistance.
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Bartak Duane E.
Lemieux Brian E.
Woolsey Earl R.
Mayekar Kishor
Niebling John
Technology Applications Group, Inc.
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