D AIMLER C HRYSLER CORPORATION No: PS-8955 Process Standard Date Published: 2004-08-10 Category Code: H-1 Change: S EASL Req. Yes
Restricted: No
ZINC ALLOY ELECTRODEPOSITED COATINGS
1.0 GENERAL
1.1 Purpo
This standard specifies the plating and performance requirements for various zinc-cobalt, zinc-nickel and zinc-iron alloy electrodeposits and their associated chromate coatings, ud for enhanced corrosion resistance on ferrous parts.
1.2 Part Drawings
Specific requirements shown on the part drawing shall take precedence over related requirements specified in this standard, or may be in addition to the requirements of this standard.
Becau this standard covers more than one zinc alloy, the chemical symbol of the alloying element must be added as a suffix after the process standard number to designate the specific alloy desired. For example, “PS-8955 Ni” for zinc-nickel, “PS-8955 Co” for zinc-cobalt, and “PS-8955 Fe” for zinc-iron alloy. If a suffix is not specified, any of the alloys covered by this standard may be ud at the discretion of the vendor.
A. The desired deposit thickness must be specified after the process standard number using a Αcode” designation. For example, the designation “PS-8955 Ni Code 30” means a zinc-nickel alloy deposit with a thickness of 8 micrometers or 0.00030 inch.
B. Parts with a hardness of Rockwell HRC 32 or greater require a mandatory bake for hydrogen embrittlement relief according to Process Standard PS-9500<S> (Hydrogen Embrittlement Relief).
C. The symbol <D> has been substituted for the diamond symbol in this standard to identify critical but non-regulatory items that require continuous Statistical Process Control (SPC). Refer to PS-7300.
D. The notation “<D> QAR per PS-7300" shall appear in the Part Drawing Standards Block.
2.0 PROCESS
2.1 Electroplating Process
Both acid and alkaline zinc alloy plating process are covered by this process standard.
2.2 Finish Requirements on Significant Surfaces
The requirements of this Standard apply to the significant surfaces of a part. Unless otherwi specified on the part drawing, significant surfaces for plating thickness and corrosion resistance determination are all surfaces that can be touched by a 19 mm (0.75 in) diameter sphere. The threads of threaded fasteners are not classified as significant surfaces. However, the entire head area of screws and bolts, and the unthreaded shanks of bolts are significant surfaces.
2.3 Workmanship
The plating shall be smooth, adherent, and free of blisters, pits, nodules, and other functional defects. Coverage shall be complete and uniform in appearance on significant surfaces, with respect to the electroplated deposit. Iridescence in the chromate finish is expected and acceptable.
2.4 Alloy Composition
The amount of alloying element prent in the zinc alloy electrodeposits covered by this standard is different for each alloy. The concentration limits for the various alloys are listed in Table 1.
NOTE: Zinc-nickel alloy deposits may be obtained from alkaline or mildly acidic plating solutions. The acidic plating process generally produce higher nickel content alloys than the alkaline systems, however alkaline systems are available which offer the same alloy content as acid systems. The corrosion resistance of zinc-nickel alloys is a function of both the alloys nickel content as well as the particular chromate conversion coating employed. In general, zinc-nickel alloy deposits containing a higher percent nickel within limits provide better corrosion protection than alloys with less nickel. However, the quality of the chromate is crucial. Accurate control of the alloy composition within the limits given in Table 1 is esntial for optimum corrosion protection.
TABLE 1: ALLOYING COMPOSITIONS AND PERMISSIBLE CONCENTRATION RANGE
DEPOSIT ALLOY WT.% RANGE OF ALLOYING
ELEMENT
NOMINAL WT.% RANGE OF
ALLOYING ELEMENT
要快乐Zinc-cobalt 0.4 to 1.0% Co 0.6% Co
Alkaline zinc-nickel 5.0 to 16.0% Ni 8.0% Ni
Acid zinc-nickel 9.0 to 16.0% Ni 12.0% Ni
Zinc-iron 0.3 to 0.8% Fe 0.5% Fe
2.5 Plating Requirements
2.5.1 Plate Thickness on Significant Surfaces
The plate thickness on significant surfaces (Section 2.2) must meet the minimum thickness as specified by the “Code” designation (refer to Section 2.5.2).
The following ASTM Standard Methods are recommended for determining the coating thickness:
- ASTM B 487 Microscopic Cross Section
- ASTM B 568 X-Ray Method
- ASTM B 499 Magnetic Method
- ASTM B 504 Coulometric Method
Except for the microscopic method, it is esntial to calibrate the test instrument with an alloy of the same composition as that being measured.
2.5.2 Minimum Deposit Thickness
The minimum coating thickness are specified by the Code number suffix after the process standard number as follows:
Code 0: Not recommended, u PS-79<S> or PS-4220<S> if color identification of parts is required; e PS-Plating.
Code 20: 5 micrometers (0.00020 in)
Code 30: 8 micrometers (0.00030 in)
astronautsDeposit thickness greater than Code 30 are generally not recommended. If it is determined that th
ickness less than Code 20 or greater than Code 30 are necessary for a particular application, drawing notes shall be ud to designate the required thickness. If no “Code” is specified on the drawing, the default is “Code 30”.
To insure compliance with the minimum thickness requirements of this standard, the plating thickness shall be measured on a regular and frequent basis using acceptable sampling plans, such as recommended in ASTM B 697, B 602, and B 762 or equivalents. Control charts and records documenting compliance with the minimum thickness requirements of this standard shall be prepared and maintained.
2.6 Chromate Type Conversion Coatings
A chromate type passivate is considered an integral part of the electrodeposited zinc alloys of this process standard. Chromated coatings significantly enhance the overall corrosion resistance of the deposit. The zinc alloy electrodeposits covered by this process standard require a hexavalent or trivalent chromate conversion coating that is formulated for the particular alloy.
NOTE: Parts submitted prior to JANUARY 1, 2007 may utilize either a hexavalent or trivalent chromate. Parts supplied beginning JANUARY 1, 2007 shall u a trivalent chromate system only. H
exavalent chromates will no longer be allowed at that time. No topcoats are allowed on fasteners and other threaded parts unless approved by Fastener Engineering. Slight color iridescence and color variations are acceptable.
The effectiveness of the chromate coating is measured by the number of hours of salt spray exposure before the development of voluminous white corrosion products. A faint white film or “blush” does not constitute a failure. Table 2 summarizes the required minimum hours of salt spray exposure before the formation of white corrosion products for the alloys and chromate coatings covered by this standard, as well as the minimum number of hours to red rust.
2.7 Performance Requirements
2.7.1 Adhesion
The deposit shall not peel from itlf or from the substrate when tested in accordance with ASTM B 571 (Standard Test Methods for Adhesion of Metallic Coatings).
The hardened, aged chromate coating shall be tightly adherent to the zinc alloy substrate and shall not be removed by ordinary handling.
2.7.2 Hydrogen Embrittlement Relief
High strength/high hardness steel parts with a Rockwell Hardness of HRC 32 or greater MUST BE PROPERLY BAKED according to the schedule and procedure specified in Process Standard PS-
9500<S>, ΑHydrogen Embrittlement Relief”, within one hour after plating. The bake operation shall be ud prior to hexavalent chromate post dip and may be done after trivalent chromate post dip, provided it can be shown that there is no detrimental effect on the corrosion resistance.
2.7.3 Hydrogen Embrittlement Test
The hydrogen embrittlement test is to be performed according to Process Standard PS-9500<S>.
2.7.4 Accelerated Corrosion Resistance
NOTE: The salt spray test is only ud to test the integrity of the alloy deposit and the effectiveness of the chromate coating. The hours to white or red rust SHALL NOT be construed as having any correlation to the actual rvice life of the part!
Sample parts shall be dried and aged for 24 hours prior to exposing them to salt spray. The test shall be conducted in accordance with ASTM B 117 for the times shown in Table 2.
Salt spray corrosion test requirements DO NOT apply to deep recess, such as small blind holes and the interior of tubing, or to non-significant surfaces.
The objective of the “Hours to White Rust” requirement in Table 2 is less than 5% white corrosion products after testing for the number of hours listed. However, chromate coatings are inherently fragile films and some damage at sharp edges, corners, etc. is to be expected. Small amounts of white corrosion products at such damage sites DO NOT constitute a failure.
On parts with a surface area greater than 155 sq cm (24 sq in), the appearance of six or more red rust spots per 1000 sq cm (1 sq ft.) of significant surface, that are visible to the unaided eye at normal reading distance or any rust spot originating from an area larger than 1.6 mm (1/16 in) in diameter is considered a failure.
On parts smaller than 155 sq cm (24 sq in), the appearance of more than one rust spot on any significant surface or any rust spot originating from a spot larger than 1.6 mm (1/16 in) in diameter is a failure.
On threaded fasteners, the formation of corrosion products in the threaded areas DOES NOT constitute a failure. However, the head and unthreaded shank of a screw or bolt is considered a sign
ificant surface and must withstand the formation of white and red rust for the minimum times listed in Table 2.
TABLE 2: MINIMUM SALT SPRAY TEST REQUIREMENTS
UNTIL JANUARY 1 2007
with hexavalent chromates
HOURS TO WHITE
RUST HOURS TO RED
RUST
ALLOY THICKNESS
(micrometers)
HEXVALENT
CHROMATE
RACK BARREL RACK BARREL
Yellow 300
240元旦的诗词
1000
720
Alkaline zinc-nickel C-
20 5 Black 240
140
1000
三维技术
720
Yellow 300
240
1000+
1000 Alkaline zinc-nickel C-
30 8 Black 240
140
1000+
1000
Yellow 400 300 1000+ 720
Acid zinc-nickel C-20
5
Black 240
140
1000
720
Yellow 400
300
1000+
1000+ Acid zinc-nickel C-30
8
Black 240
140
1000
1000 Zinc-cobalt
C-20 5 Yellow 200 140 400 300
Yellow 200 140 480 400 Zinc-cobalt C-30
8
Black 200 140 400 300 Zinc-iron C-20 5 Black 240 140 720 300 Zinc-iron C-30 8 Black 240 140 1000 400
TABLE 3: MINIMUM SALT SPRAY TEST REQUIREMENTS
JANUARY 1 2007
with trivalent chromates and a aler or topcoat
HOURS TO WHITE
RUST HOURS TO RED
RUST
ALLOY THICKNESS
脚底脱皮什么原因
(micrometers)
TRIVALENT
CHROMATE
RACK BARREL RACK BARREL CLEAR
Zinc-nickel C-20 5
240 120 840 720
CLEAR Zinc-nickel C-30 8
BLACK 240
192
120
96
960 840
Zinc-cobalt
C-20 5 CLEAR 144 96 384 300
CLEAR Zinc-cobalt C-30 8
BLACK 144
96
96
72
480 400
烟花怎么形容Zinc-iron
C-20 5 CLEAR 192 96 480 300
Zinc-iron C-30 8 CLEAR
BLACK
192
144
96
72
720 400
NOTE: The salt spray test is to be ud for process control and process capability only and not required for lot control. Salt spray corrosion testing does not need to be completed prior to shipment of parts. The corrosion testing of fasteners must follow the procedure as outlined in SAE/USCAR-1, “Salt Spray Testing and Evaluation of Fastener Finishes”.
TABLE 4: MINIMUM SALT SPRAY TEST REQUIREMENTS
JANUARY 1 2007
with trivalent chromates without a aler or topcoat
HOURS TO WHITE
RUST HOURS TO RED
RUST
ALLOY THICKNESS
(micrometers)
TRIVALENT
CHROMATE
RACK BARREL RACK BARREL CLEAR
Zinc-nickel C-20 5
192 96 790 670
长沙晚报官网CLEAR Zinc-nickel C-30 8
BLACK 192
144
96
72
900 790
Zinc-cobalt
C-20 5 CLEAR 120 72 330 250
CLEAR Zinc-cobalt C-30 8
自残BLACK 120
96
72
48
430 350
Zinc-iron
C-20 5 CLEAR 144 72 430 250
Zinc-iron C-30 8 CLEAR
BLACK
144
120
120
96
670 350
