Classification Of Surface Treatment Technology

1. Electrochemical method

This method uses electrode reaction to form a coating on the surface of the workpiece. The main methods are:

(1) Electroplating

In the electrolyte solution, the workpiece is the cathode, and under the action of external current, the process of forming a coating on its surface is called electroplating. The coating can be metal, alloy, semiconductor or contain various solid particles, such as copper plating, nickel plating, etc.

(2) Oxidation

In the electrolyte solution, the workpiece is the anode. Under the action of external current, the process of forming an oxide film on its surface is called anodic oxidation, such as the anodic oxidation of aluminum alloy.

The oxidation treatment of iron and steel can be carried out by chemical or electrochemical methods. The chemical method is to put the workpiece into an oxidation solution and form an oxide film on the surface of the workpiece by chemical action, such as the bluing treatment of steel.

2. Chemical method

This method is to form a plating layer on the surface of the workpiece by the interaction of chemical substances without current. The main methods are:

(1) Chemical conversion membrane treatment

In the electrolyte solution, the process of forming a coating on the surface of a metal workpiece by the interaction between the chemical substances in the solution and the workpiece without external current is called chemical conversion film treatment. Such as bluing, phosphating, passivation and chromate treatment of metal surface.

(2) Electroless plating

In the electrolyte solution, the surface of the workpiece is catalytically treated without external current. Due to the reduction of chemical substances in the solution, some substances are deposited on the surface of the workpiece to form a plating layer, which is called electroless plating, such as electroless nickel plating and electroless copper plating.

3. Hot working method

This method is to order material melting or thermal diffusion under high temperature conditions to form a coating on the surface of the workpiece. The main methods are:

(1) Hot dip coating

The process of putting a metal workpiece into molten metal to form a coating on its surface is called hot-dip coating, such as hot-dip galvanizing and hot-dip aluminizing.

(2) Thermal spraying

The process of atomizing molten metal and spraying it on the workpiece surface to form a coating is called thermal spraying, such as thermal spraying zinc and thermal spraying aluminum.

(3) Hot stamping

The process of heating and pressing the metal foil to cover the surface of the workpiece to form a coating layer is called hot stamping, such as hot stamping aluminum foil.

(4) Chemical heat treatment

The process of contacting and heating the workpiece with chemical substances and ordering certain elements to enter the workpiece surface at high temperature is called chemical heat treatment, such as nitriding and carburizing.

(5) Surfacing

The process of forming a welding layer by accumulating deposited metal on the surface of the workpiece by welding is called surfacing, such as surfacing wear-resistant alloy.

4. Vacuum method

This method is a process in which the material is vaporized or ionized and deposited on the surface of the workpiece in a high vacuum state to form a coating. The main method is.

(1) Physical vapor deposition (PVD)

Under vacuum, the process of vaporizing metal into atoms or molecules, or ionizing it into ions, and directly depositing it on the surface of the workpiece to form a coating is called physical vapor deposition. The deposited particle beam comes from non chemical factors, such as evaporation, sputtering, ion plating, etc.

(2) Ion implantation

The process of implanting different ions into the workpiece surface under high voltage to modify its surface is called ion implantation, such as boron implantation.

(3) Chemical vapor deposition (CVD)

Under low pressure (sometimes also under normal pressure), the process that gaseous substances generate solid deposition layer on the surface of workpieces due to chemical reaction is called chemical vapor deposition, such as vapor deposition of silicon oxide and silicon nitride.

5. Other methods

Mainly mechanical, chemical, electrochemical and physical methods. The main methods are:

(1) Painting

Idle spraying or brushing method: the process of coating (organic or inorganic) on the surface of the workpiece to form a coating is called coating, such as painting and brushing.

(2) Impact plating

The process of forming a coating layer on the workpiece surface by mechanical impact is called impact plating, such as impact galvanizing.

(3) Laser surface treatment

The process of irradiating the workpiece surface with laser to change its structure is called laser surface treatment, such as laser quenching and laser remelting.

(4) Super dural technique

The technology of preparing super hard film on the workpiece surface by physical or chemical methods is called super hard film technology. Such as diamond films and cubic boron nitride films.

(5) Electrophoresis and electrostatic spraying

① Electrophoresis

The workpiece is put into the conductive water-soluble or water-emulsified coating as an electrode and forms a circuit with the other electrode in the coating. Under the action of electric field, the coating solution has been dissociated into charged resin ions, the cations move to the cathode and the anions move to the anode. These charged resin ions, together with the adsorbed pigment particles, are electrophoresed to the surface of the workpiece to form a coating. This process is called electrophoresis.

② Electrostatic spraying

Under the action of DC high voltage electric field, the atomized negatively charged paint particles are directed to the positively charged workpiece to obtain the paint film, which is called static spraying.