TIN-LEAD ON STEEL
Description
Tin-lead alloys have a light gray color, are easy to solder and retain solderability for a long time (unlike pure tin), and provide good sintering of parts. Coatings with tin-lead alloys are used to protect products from corrosion in sea water and a number of other aggressive environments. The alloy can be deposited in a very wide range of composition.
An alloy containing 50% lead and tin each has the greatest chemical resistance. Alloys with a Sn content of 5 to 17% are used as anti-friction alloys, especially in combination with oils. Coatings of this composition also act as a lubricant when stamping parts from sheet steel.
The composition of 60% Sn and 40% Pb by weight (analogous to Gor.POS 60) is considered universal.
The standard potentials of tin and lead are close (-0.136 and -0.126 V, respectively), so they are galvanically deposited from solutions of simple salts. Lead and tin do not form either solid solutions or chemical compounds. Coating the surface of steel with a tin-lead alloy solves the following main problems: protection against corrosion of current-carrying parts of parts, protection from direct contact with aluminum (galvanic steam is corrosive to aluminum), improvement of solderability, easier screwing with simultaneous sealing of threaded connections. Can be easily brushed to improve appearance.
Advanced characteristics, as well as properties of other tin-lead alloys, can be view in the article.
You can order tin-lead coating in accordance with GOST 9.305-84 by phone and email indicated in the section "CONTACTS".
Characteristics
|
Designation (example) |
tin-lead |
|
Thickness |
9-100 microns (optimal, greater thickness is possible) |
|
Microhardness |
118-198 MPa |
|
Electrical resistivity at 18° C |
11.5⋅10-8 Ohm⋅m |
|
Permissible operating temperature |
200° C |
|
Lead content in tin-lead alloy |
60% |
Advantages tin plating:
- The coating significantly increases the solderability of the surfaces of the parts. Alloying the coating with lead allows you to maintain solderability for longer than one year;
- The tin-lead coating is resistant to sulfur-containing compounds and can be used on parts in contact with all types of plastics and rubbers;
- The tin-lead coating is extremely ductile (only pure lead is more elastic);
- Has some of the best anti-friction properties;
- Alloying with lead allows to prevent “needle formation”, and also avoids destruction of the coating during operation below minus 30°C;
- Can replace the hot-tinning coating in cases where it is necessary to obtain a thin layer, especially on threads and in the presence of holes.
Disadvantages of tin plating:
- Low abrasive wear resistance.
- Without brushing heterogeneous matte gray color and high roughness:
- The presence of lead does not allow the coating to be used for food purposes;
- The coating is unstable in an alkaline environment (primarily due to the etching of lead, which is not chemically combined with tin).
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