Electroplating
The use of electroplating has found its way into virtually every industry; these dynamic coating processes can impart a number of characteristics that enhance and improve the surface features of metal substrates. This includes appearance and corrosion resistance, special or engineered surface properties and solderability. Electroplating adds value to every substrate it is applied to.
As plating processes become more specialized, maintaining engineered specifications becomes more critical. For over 60 years we have developed plating processes that can meet these ever increasing demands. At Alexandria Metal Finishers, we specialize in electroplating, and provide the plating processes and volume capacity to meet the requirements of a broad range of industries. Our plating processes include the application of plating such as gold, silver, tin, nickel, sulfamate nickel, copper, and tin/lead in 60/40 and 90/10 ratios, as well as clear, gold, black, and olive drab zinc plating.
As with the application of any coating, a robust quality program is a critical factor in maintaining consistent results. We operate an ISO 9001 certified facility, and are in compliance with all ASTM and AMS standards; in addition, we can also accommodate virtually any mil-spec requirement for electroplating. We provide fast turnover times of same-day (if required) to three to five days, all with the same high quality consistent results.
Copper Plating
AMS-2418
MIL-C-14550
Copper plating results in a copper color and can be a matte to a very shiny finish. Copper provides good corrosion resistance when used as an undercoat. A number of copper processes are available, each designed for a specific purpose:
Brightness: To eliminate the need for buffing
High Speed: For electroforming
Fine Grain: To prevent casehardening
The thickness of the copper plating may also serve unique purpose:
| Thickness | Purpose |
| 001″ – .005 | For heat treatment stop-off |
| .001″ min | For carburizing and decarburizing shield, also plated through printed circuit boards |
| .0005″ min | As an undercoat for nickel and other platings |
| .0002″ min .0001″ min |
To prevent base metal migration into tin (prevents poisoning solderability) |
Electrolytic Nickel Plating
MIL-P-27418 (SULFAMATE NICKEL)
MIL-C-26074
AMS-2403
The two processes are very different and result in different deposit properties. Here are some things to consider when comparing electrolytic and electroless nickel processes:
| Electrolytic Nickel | Electroless Nickel |
| Non-uniform thickness of deposit. Thicknesses dependent on current density at different locations on part surface. Fixturing may be required if differences in thickness cannot be tolerated. Thickness controlled by current density and time in tank. | Uniform thickness of deposits even on parts with a complex shape as long as the part is properly prepared. No current density issues. Thickness usually controlled by time in the tank. |
| Deposit is essentially pure nickel. | Deposit is a nickel/phosphorus alloy and does not have the same physical properties as electrolytic nickel. |
| Deposit has a microhardness in the range of 250-450 VHN. | Deposit has microhardness of 340-600 VHN. If deposit is heat treated, hardness can be increased to 1000-1150 VHN range. |
| Deposit tends not to have lubricity and non-galling properties. | Deposit has some inherent lubricity and non-galling properties. |
| Thin deposits are porous. | Deposits are less porous and give better barrier corrosion protection to ferrous materials. |
| May cause hydrogen absorption, a problem with high-strength steels. | Causes reduced hydrogen absorption estimated to be less than 20% of that caused by electrolytic nickel. |
Please keep in mind that the tables are general and there are many variations in both electrolytic and electroless plating baths. As the above information indicates, electrolytic and electroless nickel are normally not interchangeable.
Alexandria Metal Finishers has several different types of baths for electrolytic nickel. Nickel can be deposited soft or hard; dull or bright, depending on process used and conditions employed in plating. Our electrolytic processes produce coatings similar to stainless steel in color or can be a light grey (almost white) color. Corrosion resistance for these coatings is a function of thickness.
Tin Plating
MIL-T-10727
ASTM-B-545
Alexandria Metal Finishers provides both “bright” and “matte” finishes of tin plating. Hot-dipped and flow brightening tin platings are not currently available. Tin plating has a gray-white appearance when plated on most metals. Tin is also a soft very ductile plating, which lends to its excellent solderability. Typically Tin is plated directly to ferrous metals with no intermediate coating. Tin is not good for low temperature applications because it changes structure and loses adhesion when exposed to temperatures below -40c.
Tin/Lead Plating
AMS-P-81728
MIL-P-81728
ASTM-B-579
Alexandria Metal Finishers provides both “bright” and “matte” finishes of tin/lead plating. Like regular tin plating, tin/lead plating has excellent solderability, but unlike tin plating tin/lead minimizes the risk of tin whiskers. Whiskers can cause failure of electrical components by bridging multiple conductor paths causing a short circuit. As devices get smaller and smaller, the potential for catastrophic failure due to whiskers will increase. As the name suggests this plating material is a mixture of Tin(Sn) and Lead(Pb). The standard composition of our tin/lead baths is about 60% tin and 40% lead, this ratio providing the lowest melting point possible for this combination. We do offer this plating with a 90/10 or 95/5 Sn-Pb ratio. WIth tin/lead plating, the higher the tin composition, the higher the abrasion resistance.
Zinc Plating
ASTM-B633
QQ-Z-325
Alexandria Metal Finishers offers four types of zinc plating within the ASTM-B633 specification. Zinc can be a bright or dull finish. Bright zinc resembles bright chromium, but does not have the permanence of surface appearance. With weathering, zinc will turn a drab gray color. Parts having a hardness > Rc-31 should be given a heat treatment prior to plating to combat hydrogen embrittlement. Parts having a hardness > Rc-39 should be given a bake after plating for 3-4 hours at 375 deg F +/- 25 deg F.
Zinc coatings prevent oxidation of the protected metal by forming a barrier and by acting as a sacrificial anode if/when the barrier is damaged. Zinc oxide is a fine white dust that does not cause a breakdown of the substrate’s surface integrity as it is formed. This is an important distinction because zinc is commonly used on ferrous parts and iron oxide (rust), is greatly inhibited by an application of zinc. Indeed the zinc oxide, if undisturbed, can act as a barrier to further oxidation, in a way similar aluminum and stainless steels are protected by their oxide layers. The majority of hardware parts are zinc plated.