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Sheet metal materials and surface treatment processes, what do you know?

In sheet metal fabrication, the commonly used methods of surface treatment include electro-galvanizing, chrome plating, powder spraying, electrophoresis, and dipping. No matter which method is used, attention must be paid to the cleaning of the material before surface treatment.

8 commonly used sheet metal materials

  1. Cold-rolled sheet, grade SPCC. The most basic sheet metal material has a wide range of uses. It is used as a base material for other materials and is relatively easy to rust.
  2. Electro-galvanized sheet, grade SECC, widely used is obtained by electroplating with the cold plate as the base material, which is the result of a chemical reaction.
  3. Hot-dip galvanized sheet, grade SGCC, has a wide range of uses. It is the product of using a cold plate as the base material and heating it in a molten zinc solution to form a zinc layer. The production process is a physical change process.
  4. Hot-rolled sheet, grade SPHC, is a low-end material that is easy to rust, and the thickness is generally more than 3mm. Usually used for hinge products.
  5. SD steel plate is a plate with excellent anti-rust and anti-corrosion properties. The mounting bracket of the outdoor unit of the air conditioner uses this material.
  6. Stainless steel and stainless iron, typical grades SUS304 and SUS430, are alloy materials. It has good anti-rust and anti-corrosion performance, and the surface is relatively beautiful. It is usually used for exterior parts, such as refrigerator door casings and gas stove tops.
  7. Galvanized sheet seems to be a type of electro-galvanized sheet, but it has one more metal aluminum element than an electro-galvanized sheet, so the surface is smoother and more beautiful, and it is often used for exterior parts, such as the back steel plate of a certain type of refrigerator.
  8. Aluminum plate or aluminum alloy plate, also known as aluminum sheet. Low density and anti-corrosion, typical products: refrigerator water trays and evaporator fins, etc.

Sheet Metal Material Cost

Cost comparison

In the case of the same thickness: hot-rolled sheet < cold rolled sheet < hot zinc sheet < electro-zinc sheet < SD steel sheet < stainless iron < stainless steel

For the same material, the larger the thickness, the lower the price.

In the cost of sheet metal parts, the material cost basically accounts for 60-70%, and sometimes it is higher.

Therefore, it is necessary to design a reasonable structure, and it is also necessary to improve the utilization rate of materials. If the utilization rate of materials is low, the price of the product may be lower than the price of the scrap.

Why should the sheet metal surface be treated?

Since some sheet metal materials do not have the ability to prevent rust and corrosion, they need to be surface treated to achieve their goals.

There are two main purposes of surface treatment:

  • Improve product life in harsh environments: anti-rust and anti-corrosion capabilities.
  • To obtain the desired surface effect or function: meet the appearance requirements of the product.

8 common surface treatment processes for sheet metal

In sheet metal fabrication, the commonly used methods of surface treatment include electro-galvanizing, chrome plating, powder spraying, electrophoresis, and dipping. No matter which method is used, attention must be paid to the cleaning of the material before surface treatment.

Sheet metal materials and surface treatment processes
Sheet metal materials and surface treatment processes


Electro-galvanizing: It is the process of using electrolysis to form a uniform, dense and well-bonded metal or alloy deposition layer on the surface of the workpiece.

Compared with other metals, zinc is a relatively cheap and easily plated metal, and it is a low-value anti-corrosion coating. It is widely used to protect steel parts, especially against atmospheric corrosion, and for decoration. Plating techniques include tank plating (or rack plating), barrel plating (suitable for small parts), automatic plating, and continuous plating (suitable for wire, strip).

4 Commonly Used Galvanizing Processes

The classification of electroplating solutions in China can be divided into four categories:

  • Cyanide Zinc
    Since (CN) is highly toxic, environmental protection has put forward strict restrictions on the use of cyanide in electro-galvanizing, and constantly promotes the development of cyanide-reducing and replacing cyanide electro-galvanizing bath systems, requiring the use of low-cyanide (micro-cyanide) electroplating baths. After electroplating by this process, the product quality is good, especially the color plating, the color remains well after passivation.
  • Zinc galvanized
    This process evolved from cyanide zinc plating. At present, two major factions have formed in China, namely: a) “DPE” series of Wuhan Material Insurance Institute; b) “DE” series of Radio and Television Institute. All are zincate galvanized with alkaline additives; the PH value is 12.5~13. Using this process, the lattice structure of the coating is columnar, and the corrosion resistance is good, which is suitable for color galvanizing.
  • Chloride Zinc
    This process is widely used in the electroplating industry, accounting for up to 40%. After passivation (blue-white), chrome can be replaced by zinc (comparable to chrome plating), especially after adding water-soluble varnish, it is difficult for a layman to distinguish whether it is galvanized or chrome plated. This process is suitable for white passivation (blue-white, silver-white).
  • Sulfate Zinc
    This process is suitable for continuous plating (wire, strip, simple, thick and large parts, components). low cost.

Notes: The electro-galvanizing industry is a polluting industry. Although it is widely used and has a low cost, electro-galvanizing products do not meet the ROHS standard, so try not to use electro-plating products in product design.

Chrome plating

The principle of chrome plating is the same as that of galvanizing.

Compared with traditional electro-galvanizing, chromium coating has extremely strong corrosion resistance, which is 7-10 times that of galvanizing and has a beautiful surface, but the cost is higher.

At present, the most advanced chrome plating process is called DACROMET, which is a revolutionary high-tech metal surface treatment process, and the whole process is pollution-free.

Powder spraying

Powder spraying: The powder is polarized and uniformly adheres to the surface of the product with the opposite polarity under the action of the electric field force. are physical changes.

Powder spraying process principle:

Electrostatic powder spraying: mainly polarize the paint (powder) through the electrode, and then charges the object to be sprayed with the opposite charge, and the powder uniformly adheres to the surface of the object under the action of the electric field force.

Features of powder spraying process:

Powder electrostatic spraying will not cause atmospheric pollution, the powder can be recycled to reduce the consumption cost of materials, and the coating film has excellent acid resistance, alkali resistance, salt resistance, good corrosion resistance, and high adhesion.


Electrophoresis: Under the action of the cathode and anode, the charged paint ions move to the surface of the product and deposit to form a coating. is a chemical change.

The process principle of electrophoresis:

Electrophoretic paint is applied to the cathode and anode under the action of voltage, and the charged paint ions move to the cathode and form insoluble matter with the alkaline effect generated on the surface of the cathode, which is deposited on the surface of the workpiece.

Features of electrophoresis surface treatment process:

Electrophoretic paint film has the advantages of a full, uniform, flat, and smooth coating. The hardness, adhesion, corrosion resistance, impact performance, and penetration performance of electrophoretic paint film are obviously better than other coating processes.

The common electrophoresis color is mostly black, and other colors are also available.


Metal dipping: The product is heated in the molten material, and the heated metal is combined with the surrounding molten material to form a surface material of a certain thickness. These are physical changes.

The process principle of dipping:

Metal dipping is a new type of technical treatment process for metal surface anti-corrosion. Dipping is a heating process, metal preheating, dipping, and curing. During dipping, the heated metal sticks to the surrounding material. The hotter the metal, the longer the dipping time and the thicker the material.

The process characteristics of metal dipping:

Wide range of applications: rich colors, good protection, excellent cold resistance, heat preservation, and acid and alkali resistance.


Oxidize the metal on the surface of the workpiece to form a dense protective film on the surface of the workpiece to increase the corrosion resistance of the workpiece. Generally, there are two ways of chemical oxidation and anodic oxidation. It is a common surface treatment method, usually with primary color anodizing and black anodizing. A common material for this surface treatment process: aluminum.


The process of silk-screening various logos on the surface of the material generally has two methods: flat-screen printing and pad printing. The main principle is the same as that of camera film imaging, which is also an exposure process. Flat-screen printing is mainly used on general planes, but if there are deep pits, pad printing is required. Usually used in trademarks, usage signs, warning signs, etc.


Phosphating is a commonly used pretreatment technology, and in principle, it should belong to chemical conversion film treatment. It is mainly used for phosphating on steel surfaces, and non-ferrous metals (such as aluminum and zinc) can also be phosphating.

The main purpose of phosphating is to provide protection for the base metal and prevent the metal from being corroded to a certain extent; it is used as a primer before painting to improve the adhesion and anti-corrosion ability of the paint film; it is used to reduce friction in the metal cold working process. Lubrication. Common materials for this surface treatment process: cold-rolled sheet, hot-rolled sheet.