What is aluminum alloy electroplating

The surface of aluminum and aluminum alloy is treated by electroplating process, which is a common surface treatment method. Aluminum alloy has the advantages of good electrical conductivity, fast heat transfer, light specific gravity, and easy molding. Electroplating different metals on its surface can improve physical and chemical properties in different directions to meet different usage scenarios and needs.

The advantages of aluminum alloy plating

• 1 Improve decoration,

• 2 Improve surface hardness and wear resistance

• 3 Reduce friction coefficient and improve lubricity.

• 4 Improve surface conductivity.

• 5 Improve corrosion resistance (including combination with other metals)

• 6 Easy to solder

• 7 Improve the bonding force when it is hot-pressed with rubber.

• 8 Improve reflective rate

• 9 Fix dimensional tolerances

Process flow of aluminum alloy electroplating

At present, in the field of surface treatment, the electroplating process of aluminum alloy is still in the exploratory stage, and there is no unified, perfect and standard process flow. Generally speaking, the aluminum alloy electroplating process can be divided into two types: traditional and improved.

1 Traditional aluminum alloy electroplating

The aluminum alloy electroplating process consists of three parts: pre-plating treatment, electroplating, and post-plating treatment. Pre-plating treatment is the most critical process related to the quality of electroplating products. Its main purpose is to remove the grease on the surface of aluminum and aluminum alloys, and naturally form oxide films and other dirt.

The conventional general process flow is: degreasing-water washing-corrosion reduction-water washing-pickling-water washing-activation-water washing-first zinc immersion-water washing-zinc stripping-water washing-secondary zinc immersion-water washing-neutral nickel plating-water washing- Subsequent plating.

Deficiencies in the traditional pretreatment process

• (1) The process flow is long and there are many processes.

• (2) The process is complex, the operating range is narrow, and the process parameters are troublesome.

• (3) The scope of application of the process is not wide.

• (4) Under the premise of strictly controlling the pre-treatment process, the qualified rate of electroplating products is very low, the average qualified rate of ordinary decorative electroplating is 88%, and the average qualified rate of functional electroplating is 65%.

• (5) The service life of the process solution is short and the processing cycle is short.

2 Improvement of aluminum alloy electroplating process

Degreasing and alkali etching two-in-one-water washing-acid washing-water washing-ash removal-water washing-alkaline activation-zinc dipping-water washing-neutral nickel plating-water washing-subsequent electroplating.

The use of common plating types

• 1 Black plating, such as black zinc, black nickel, etc. are used in optical electronics and medical equipment.

• 2 Gold plating and silver are the best conductors of electronic products, and can also improve the high-level decoration of products, but the price is relatively expensive, and are generally used in the electrical conductivity of electronic products, such as electroplating of high-precision wire terminals.

• 3 Copper, nickel, and chromium are the most popular mixed plating species in the field of modern science. No matter in decoration or corrosion resistance, they are the most popular plating species in the world at present. Low price, can be used in sports equipment, lighting, most of the electronic industry.

• 4 Among the copper-based plating types, white tin copper was developed in the 1970s and 1980s for environmental-friendly plating types. It is white and bright, and is the first choice for the jewelry industry. Bronze (lead-tin-copper can be used as imitation gold, so it is a better decorative plating), but copper has poor anti-tarnish property, so its development is relatively slow.

• 5 Zinc-based electroplating: The galvanized layer is bluish white and easily soluble in acid and alkali. Since the standard potential of zinc is more negative than that of iron, it can provide reliable electrochemical protection for steel. Zinc can be used as a protective layer for steel products used in industrial atmospheres and marine atmospheres.

• 6 Hard chromium, the chromium coating deposited under certain conditions has high hardness and wear resistance, and the hardness reaches HV900-1200kg/mm. Chromium is the hardest coating among commonly used coatings, which can improve the wear resistance of parts ,Extended service life. This type of plating is an indispensable treatment method for cylinders, oil pressure and transmission systems.

Common abnormalities and improvement measures

1 Peeling

• (1) The zinc replacement is not good, the time is too long or too short, and the improvement measures are to re-determine the replacement time, bath temperature, bath concentration and other operating parameters.

• (2) The activation is not enough. Improve measures and change the activation method.

• (3) The pre-treatment is not complete, there is oil on the surface of the workpiece, and the improvement measures should be strengthened.

2 Rough surface

• (1) Electroplating liquid light agent, softener, pinhole dosage is not suitable, re-adjust the amount of additives.

• (2) The surface of the body itself is rough, and it must be re-polished before electroplating.

3 The yellowing of the surface means that the trend of low potential is not correct, so change the installation method. Add an appropriate amount of walking agent.

4 Raised teeth on the surface: the electroplating solution is too dirty, strengthen filtration, and make proper bath treatment.

Quality requirements

• 1 The appearance has no yellowing, pinholes, burrs, blisters, bruises, scratches and other adverse phenomena.

• 2 The film thickness is more than 15um, and the salt spray test is 48 hours, reaching the US standard level 9 or more, and the potential difference is in the range of 130-150mv.

• 3 The binding force can pass the 60-degree bending test.

• 4 For products in special environments, corresponding changes can be made.

Matters needing attention in electroplating operation of aluminum and aluminum alloy

• 1 Aluminum alloy should be used as hanger for electroplating of aluminum parts;

• 2 After the etching of aluminum and aluminum alloys, each process must be carried out quickly, and the interval between processes should be as short as possible to avoid re-oxidation;

• 3 The second galvanizing time should not be too long to avoid over-corrosion;

• 4 Washing must be cleaned;

• 5 During the electroplating process, it is necessary to prevent midway power failure.