Process for Electroless Deposition on Magnesium Using a Nickel Hydrate Plating Bath

Abstract

A plating process using an electroless plating bath formed from a single component solution used to effect nickel or nickel alloy plating on magnesium. The plating solution is provided with a nickel hydrate compound as a source of plating ions, a sodium hydrate compound and ammonium hydroxide. The bath solution is heated to a temperature of 50° C. or more, and the substrate is immersed therein for upto ten minutes to allow for formation of the heating layer.

Description

RELATED APPLICATIONS[0001]This application claims the benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61 / 599640, filed Feb. 16, 2012.SCOPE OF THE INVENTION[0002]The present invention provides a method and process of electroless coating of magnesium and magnesium alloy substrates with metal coatings and more preferably, coatings of nickel phosphorus (Ni—P) and / or its alloys, including zinc (Zn) in the form of (Ni—Zn—P) and (Ni-p-Zn) and / or Tungsten (W) in the form of (Ni—W—P), as for example part of a method of preventing the galvanic corrosion of magnesium.BACKGROUND OF THE INVENTION[0003]Magnesium is the eighth most abundant metal on earth. Magnesium is two-thirds the weight of aluminum; whilst having physical and mechanical properties approaching that of steel; and is easy to form and machine. Heretofore, the use of magnesium in commercial metal fabrication applications has been limited due to its extreme susceptibility to galvanic corrosion, particularly whe...

AI Technical Summary

Benefits of technology

The present invention provides a plating process for the deposition of metal coatings directly on magnesium and magnesium alloy substrates using a nickel hydrate plating bath. This process overcomes the disadvantages associated with conventional electroless plating processes and provides a more efficient and effective method for plating these metals. The plating bath solution is prepared as a single component solution with a pH of at least 10 and heated to a temperature of at least 50°C. The solution includes a nickel hydrate compound, such as nickel acetate tetrahydrate, nickel sulfate hexahydrate, or nickel sulfamate tetrahydrate, and a sodium hydrate compound, such as sodium citrate tribasic dihydrate or sodium hypophosphite hydrate. The plating process involves immersing the substrate in the heated solution for a short period of time and then optionally rinsing it with a solution containing a chloride salt. The invention also provides a method for electroless plating a plating metal on a magnesium or magnesium alloy substrate using a plating bath solution containing a nickel hydrate compound and one or more of nickel acetate tetrahydrate, nickel sulfate hexahydrate, or nickel sulfamate tetrahydrate. The plating process is efficient, effective, and can produce uniform coatings on magnesium and magnesium alloy substrates.

Problems solved by technology

Heretofore, the use of magnesium in commercial metal fabrication applications has been limited due to its extreme susceptibility to galvanic corrosion, particularly when it is placed in contact with metals other than aluminum and zinc, in the presence of electrolytes.

In particular, it has therefore been generally accepted that electroless coating is so excessively slow, that it cannot be commercially achieved at pH levels of 11 or higher.

Oxidized metal surfaces are generally understood as unsuitable bonding sites for any metal, including metals deposited by electroless coating processes.

This in turn may result in the formation of a poor finish, poor adhesion around oxidized and corroded areas, and / or intermittent coverage of the coating layer over the magnesium surface.

As a multi-step process, however, the requirement of pre-coating with copper has yet to receive widespread commercial acceptance by magnesium parts manufacturers, other than for use as decorative magnesium parts requiring chrome finishes.