① Lead-based or tin-based bearing alloys. Collectively with the lead-based bearing alloys are known as the Bartholomew alloys. Contains antimony 3% to 15%, copper 3% to 10%, some alloy varieties also contain 10% of lead. Antimony and copper are used to improve the strength and hardness of the alloy. Its small coefficient of friction, good toughness, thermal conductivity and corrosion resistance, mainly used to manufacture sliding bearings.

② Lead-tin solder. Tin-lead alloy is the main, some tin solder also contains a small amount of antimony. Tin alloy containing 38.1% lead is commonly known as solder, melting point of about 183 ℃, used in the electrical instrumentation industry in the welding of components, as well as automotive radiators, heat exchangers, food and beverage containers, such as sealing.

③ Lead-tin alloy coating. The use of tin alloy corrosion resistance, it will be coated on the surface of various electrical components, both protective, but also decorative. Commonly used are tin-lead system, tin-nickel system coating, etc.

Lead-tin alloys (including lead-tin alloys and lead-free tin alloys) can be used to produce a variety of fine alloy jewelry and alloy crafts, such as rings, necklaces, bracelets, earrings, brooches, buttons, tie clips, caps, craft ornaments, alloy photo frames, religious emblems, miniature statues, souvenirs, etc.

Features

1. Lead-tin alloy has stable performance, low melting point, good fluidity and low shrinkage.

2. Lead-tin alloy has fine grain, good toughness, suitable softness and hardness, smooth surface, no sand holes, no blemishes, no cracks, good polishing and electroplating effect.

3. Lead-tin alloy has good centrifugal casting performance, strong toughness, can cast complex shape, thin-walled precision parts, smooth casting surface.

4. Lead-tin alloy products can be surface treated: electroplating, spraying, painting.

5. The dense crystal structure of lead-tin alloy ensures small dimensional tolerance of castings, fine surface and few post-treatment defects in terms of raw materials.

In the acidic electrolyte with simple complex ions, lead-tin alloy can produce co-deposition at very low current density, and lead-tin alloy plating has lower porosity than lead plating and tin plating of the same thickness. Lead-tin alloy containing 60% tin and 40% lead has the lowest eutectic point of 183℃, and its soldering performance is much higher than that of pure tin plating. Therefore, it has been widely used in the aerospace, electronic and electrical industries . Stable performance, low melting point, good fluidity and low shrinkage. Fine grains, good toughness, soft and hard, smooth surface, no sand holes, no blemishes, no cracks, good polishing and plating effect.

Plating lead-tin alloy

Lead-tin alloy plating is widely used in industry. By changing the concentration ratio of two metal ions in the plating solution, various lead-tin alloys with different lead and tin contents can be obtained. Plating containing 6% to 10% tin alloy plating on the steel strip can improve the corrosion prevention ability, solderability and bonding with the paint, and has good lubricating properties; 15% to 25% tin plating is commonly used for surface lubrication, adhesion aid, soldering aid; 45% to 55% tin alloy plating can be used to prevent corrosion of seawater and other media; 55% to 65% tin plating can improve the solderability of the surface of electronic components . The addition of 1% to 3% of lead in pure tin can prevent the generation of "tin whiskers". The content of tin in lead-tin alloy plating increases with the content of tin in the plating solution and the increase of current density.

The difference between the standard electrode potential of lead and tin is very small (-0.126V for Pb/Pb2+ and -0.136V for Sn/Sn2+), and the hydrogen overpotential is high, so the ratio of lead to tin content in the plating solution and the current density can be controlled to achieve co-deposition in a simple strong acidic plating solution to obtain various required ratios of lead-tin alloy plating.

1) The alloy plating with 5%-15% tin mass fraction has good anti-corrosion and lubricating properties and is commonly used for corrosion protection of steel products.

2) Tin mass fraction of 6% to 20% of the alloy plating excellent wear reduction performance, commonly used in the sliding bearing surface plating.

3) Tin mass fraction of 60% to 65% alloy plating corrosion resistance and excellent solderability, commonly used for printed circuit board plating.

4) The alloy plating with 75% to 90% tin mass fraction has good solderability and is often used for plating of electronic component leads.

5) If 1% to 3% of lead is added to pure tin plating, it can effectively prevent the formation of tin whiskers.

Properties of lead-tin alloys

The most important of lead-based alloys is lead-tin alloy. This alloy has a light gray metallic luster, is relatively soft, and has lower porosity than monolayer lead or tin. The standard electrode potential difference between lead and tin is only 10mV, and the overpotential of hydrogen is high, so it can be co-precipitated in simple strong acidic plating solution, and the alloy plating layer of any kind of alloy composition can be obtained by just controlling the lead-tin ion concentration ratio and current density, and its current efficiency is close to 100%.

In addition to the most used fluoroborate plating solution for lead-tin alloys, amino sulfonate, phenol sulfonate, alkanol sulfonate and citrate plating solutions have been used in production.

The metallographic organization of lead-tin alloys is a supersaturated solid solution, but phase changes occur gradually during storage. In some special cases, the components will also form intermetallic compounds with the substrate, such as tin and copper, and this characteristic has special requirements for the occasion, should be considered in its substrate and lead-tin alloy plating with an intermediate layer between the plating.

The melting point of tin-lead alloy is lower than pure tin and pure lead, and it has the outstanding advantage of better porosity and solderability than monometal. Such as pure tin plating for a long time, the surface will grow needle-like crystals (tin whiskers), can cause a short circuit; in the low temperature can also produce "tin plague". In the pure tin as long as the addition of 2% to 3% or more of lead, this phenomenon is not easy to occur. Therefore, this plating is the most important solderable plating in electronic components.

Lead-tin alloys with different amounts of tin have different properties and uses. In general, the use of various lead-tin alloys is determined by the alloy composition they contain.

The composition of lead-tin at the lowest eutectic point (183°C) is 61.9% tin and 38.1% lead, at which time the alloy has the greatest solder strength and wetting ability, so most of the current solder and solder coatings are 60% tin and 40% lead alloy coatings.

Applications

Lead-tin alloys with different tin content have different properties and applications. Usually the use of various lead-tin alloys is determined by the different alloy composition they contain.