DELPHI-I - DELPHI DX551300
CORROSION PROTECTIVE COATINGS – ZINC ALLOY PLATING (HEXAVALENT CHROMIUM FREE)
|Publication Date:||1 December 2011|
This specification covers the basic requirements for a barrel or rack electrodeposited zinc alloy plating system over a ferrous substrate. A plating system consists of; zinc alloy plating, a zinc-alloy surface treatment (e.g. trivalent chromium conversion coating), and may include a post treatment. All zinc alloy surface treatments and post treatments must be hexavalent chromium free. Five alloy platings are covered by this specification: zinccobalt, zinc-nickel [standard], zinc-nickel [high nickel content], zinc-iron and zinc-cobalt-iron. Zinc alloy plating is especially suitable for small to medium ferrous parts such as castings, fasteners, stampings, clips and other parts where levels of corrosion protection exceeding pure zinc are required. Table 1 lists the zinc alloy finishes covered by this specification and their alloy concentration limits and % nominal.
NOTE: These finishes are not recommended for applications where white corrosion is a cosmetic concern.
The specification number shown in the title is a generic number for the different zinc alloy plating finishes. Table 2 shows the specification numbers to be used on the drawings and reflects the basic requirements of the specification. The alloy's designation should be included in the drawing call out.
Drawing call out example: Zinc-Iron Alloy Plating, DX551302 per DX551300.
This example from Table 2 indicates a zinc-iron plating with a 8 micrometer minimum thickness that has a zinc alloy surface treatment. The coating must withstand a minimum of 600 hours neutral salt spray without evidence of base metal corrosion (red rust). A general topcoat is added to enhance the corrosion resistance. The presence of a letter after the specification number (example: DX551302-F) indicates an Approved Source Qualification Suffix per DX550083 requirement per DX550083, as described in Section 11.
Specific requirements shown on the part drawing shall take precedence over any requirements in this specification, or may be in addition to the requirements of this specification.
Some colors are obtained by the use of specific zinc alloy surface treatments, post-treatments or color dyes.
The use of zinc alloy plating and related finishes described in this specification on threaded surfaces and/or bearing surfaces of joints could affect the torque-tension relationship. It is recommended that a torque-tension study of the fastener joint be performed before releasing the specified plating and finishes for use on new threaded applications. See Table 1 of this specification.
Zinc alloy plated parts or their corrosion products must not come in contact with stressed Polyamides 6 or 66.