Surface pre-treatment method for pre-coated heat-treatable, precipitation-hardenable stainless steel ferrous-alloy components and components coated thereby

Abstract

The present invention relates to the use, in a pre-coating process, of a flash plating, without a subsequent chromate seal, as a surface pre-treatment for a ferrous-alloy substrate prior to applying a corrosion-inhibiting coating to improve the overall corrosion protection of the pre-treatment component. Preferably the ferrous alloy is a heat-treatable, precipitation-hardenable stainless steel and the pre-treatement is a cadmium flash plate or a zinc-nickel alloy flash plate.

Description

[0001] This invention relates to the preparation of pre-coated ferrous-alloy components. More particularly, the present invention relates to the use of a surface preparation as a preliminary step in a pre-coating process to improve the corrosion protection and other properties of coated ferrous-alloy components.[0002] Aircraft manufacturers use a variety of different ferrous and non-ferrous metals in the fabrication of aircraft components. Commonly assigned U.S. Pat. No. 5,614,037 discloses a method for pre-treating aluminum and aluminum-alloy articles to obviate the use of wet sealants and other coatings for protection against corrosion damage.[0003] Ferrous alloys such as carbon steels and aircraft-quality low-alloy stainless steels, such as, for example, Aermet 100, HY-TUF.TM., 300M, H-11, HP9-4-30, 52100, 1095, 4130, 4135, 4140, 4330V, 4340, 6150, 8740, 18-8, 17-4PH, 17-7PH, 15-5PH, PH 13-8Mo, PH 15-7Mo, A-286, etc. are often used as primary structural aircraft components. Typic...

AI Technical Summary

Benefits of technology

The present invention relates to a method for improving the final condition of heat-treated, precipitation-hardenable stainless steel ferrous-alloy components by using a flash plating process with a specific surface pre-treatment before applying a corrosion-inhibiting coating. The pre-treatment process involves flash plating with either a cadmium or zinc-nickel alloy flash plate, followed by the application of a curable organic coating material that is curable at the same temperature as the ferrous-alloy substrate. The coated component is then heat-treated to simultaneously cure the coating and the component. The invention provides a better pre-determined final condition of the component, resulting in improved corrosion protection. The invention also includes a method for coating the ferrous-alloy component with a curable organic coating material and a curing process. The invention is useful for improving the corrosion resistance of ferrous-alloy aircraft structural components.

Problems solved by technology

These fasteners are often installed using a labor-intensive, time-consuming, and, consequently, very costly wet-sealant process.

However, cadmium is suspected of being a carcinogen and is a known toxic element.

Although several candidate coatings have been identified, no single replacement coating or system has been found that meets all of the engineering requirements.

However, it has been shown that, with respect to pre-coated components having different ferrous-alloy substrate materials, while the surrounding structural components are adequately protected to equivalent levels from corrosion attack, the coating itself that is applied to some of the components in known pre-coating processes may be adversely affected from an appearance standpoint and may interact to a degree that is visually perceptible.

Over a prolonged period of time, the possibility exists that the adverse effect of this interaction could not only manifest itself in the coating's visual appearance but may also have an effect on the coating's integrity, possibly leading to a compromised corrosion protection condition.

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