GMNA - GM4344M
Corrosion Protective Coatings, Zinc Plating
|Publication Date:||1 March 2005|
Specification GM4345M describes the basic requirements of electroplated zinc coatings on iron and steel substrates with provision for plating thickness, passivation treatment, color and salt spray requirements. The plating to this specification shall be chromate without any dipping solution, sealer, lubricant or any other chemical applied on top of chromate.
For the optional use of electroplating or mechanical (peen) plating GM4344M is also included as part of this specification. Provision is also made to specify mechanical plating only.
Note 1: Drawings with GM4342M designation with customary unit suffixes may be encountered. Contact materials engineer to determine the equivalent metric unit suffixes (GM4345M).
Material Description. The current zinc plating with passivation (K,D,B and E in Table 1) contains hexavalent chromate. These will be discontinued effective December 2005 or Model Year 2006 parts whichever is earlier. Table 2 shows the substitute finishes for GMNA.
Note 2: The surface lubricity of the substitute finish GMW3044 with suffix "N" is similar to that of GM4345M. The surface lubricity and other requirements of GMW4205 and GM6047M Code G (other recommended substitute finishes shown in Table 2) are different than those of GM4345M. Contact Materials Engineer for detail information
Note 3: This plating shall not be used on new designs. Contact Materials Engineer to substitute an appropriate code of GMW3044. Note the surface lubricity of GMW3044 could be different than that of GM4345M
Note 4: For GMNA conformance to the hexavalent chromate free requirements per GMW3059 is mandatory. For other GM regions the responsible Engineering group should be contacted if deviations are required for local programs.
Table 1 lists the common types of finishes covered by this specification. However, it may be necessary to devise additional combinations of finishes within the framework of this specification as follows:
1. the first one or two digits depict the plated metal thickness in micrometers,
2. the next character indicates uncoated zinc or supplementary treatment as shown in Table 1;
3. the remaining digits indicate corrosion requirements to base metal corrosion and zinc corrosion products as specified in Table 1.
When color is specified, the desired color is appended to the suffix.
Example: GM4345M 9D120/48 (bright-yellow) indicates a zinc plated finish, color dyed bright yellow, 9 µm minimum thickness, passivated or conversion coated to withstand 120 h neutral salt spray without evidence of base metal corrosion and 48 h neutral salt spray to zinc corrosion products.
Use of this finish on threaded surface and/or bearing surface of joints could affect the torquetension relationship. It is recommended that a torque-tension study of the fastener joint be performed before releasing this finish on a new application.