What is Metal Surface Treatment-Surface Finishing Process

Metal surface treatment or machining surface finish, is a process method of artificially forming a surface layer on the surface of the substrate material, which is different from the mechanical, physical, and chemical properties of the substrate. In a broad sense, Metal surface treatment includes pretreatment, electroplating, painting, chemical oxidation, thermal spraying, spraying surface, and many other physical and chemical process methods. Pretreatment includes sandblasting, polishing, mechanical grinding, cleaning, sweeping, deburring, degreasing, descaling, surface heat treatment, etc. The purpose of metal surface treatment is to meet the product’s corrosion resistance, wear resistance, decoration or other special functional requirements.

Surface Treatment

How to improve surface finish inmachining

In the process of processing, transportation, storage, etc., the surface of the workpiece is often covered with oxide scale, rust molding sand, welding slag, dust, oil, and other dirt. If the coating can be firmly attached to the workpiece, the surface of the workpiece must be cleaned before painting. Otherwise, it will affect the bonding force and corrosion resistance between the coating and the metal. Even more, it also makes the matrix metal continue to corrosion even if there is coating protection. So it will cause the coating to peel off and affect the mechanical properties and service life of the workpiece. Therefore, the metal surface treatmentof the workpiece before painting is an important guarantee and measure to obtain a high-quality protective layer and prolong the service life of the product.

Benefits of Metal Surface Treatment

– Improve surface hardness
– Improve wear resistance
– Corrosion resistance
– Enhanced chemical resistance
– Good adhesion
– resize

– Improve appearance
– Add specific colors
– change gloss
– reduce friction
– remove surface defects
– Clean parts

Surface Treatment

In terms of technology,metal surface treatment can be classified as follows

Electrochemical -method

1.Electrochemical method

This method uses electrode reaction to form a coating on the surface of the workpiece.

Chemical-method

2. Chemical method

This method is no current action and uses chemical interaction to form a plating layer on the surface of the workpiece.

Hot-working-methods

3.Hot working methods

The material is melted or thermally diffused under high-temperature conditions to form a coating on the surface of the workpiece.

Vacuum-method

4. Vacuum method

This method is no current action and uses chemical interaction to form a plating layer on the surface of the workpiece.

Other-methods

5.Other methods

There are Mainly mechanical, chemical,
electrochemical, physical methods.

All the methods of surface treatment can be subdivided as follows

Classification by technology	Subdivision	Interpretation	Surface treatment name
Electrochemical method	Electroplate	In the electrolyte solution, the workpiece is the cathode,and the process of forming a coating on the surface under the action of external current is called electroplating. The coating may be metal, alloy,semiconductor, or containing various solid particles.	Copper plating, Nickel plating
Electrochemical method	Oxidation	In the electrolyte solution, the workpiece is the anode, and the process of forming an oxide film on the surface under the action of external current is called anodic oxidation.	Anodizing of aluminum alloys
chemical method	Chemical conversion coating treatment	In the electrolyte solution, the metal workpiece is in the absence of external current action. The chemical substance in the solution interacts with the workpiece to form a coating on its surface, which is called chemical conversion coating treatment	Bluing, phosphating treatment, passivation treatment and chromate treatment of metal surface
chemical method	Electroless plating	ln the electrolyte solution, the surface of the workpiece is catalytically treated without the action of external current. Due to the reduction of chemical substances in the solution, certain substances are deposited on the surface of the workpiece to form a plating process called electroless plating.	Electroless nickel, electroless copper plating
Hot working methods	Hot dip coating	The process in which a metal workpiece is placed in molten metal to form a coating on its surface is called hot dip cating.	Hot dip galvanizing, hot aluminizing plating
	Thermal spraying	The process of atomizing molten and spraying it on the surface of the workpiece to form a coating is called thermal spraying.	Thermal zinc spray, thermal spray aluminum
	Hot stamping foil	The process of heating and pressing metal foil to cover the suface of the workpiece to form a coating layer is called hot stamping foil.	Aluminum foil hot stamping
	Chemical heat treatment	The process of contacting and heating the workpiece with chemical substances and making a certain element enter the surface of the workpiece under high temperature is called chemical heat treatment.	Nitriding process, carburizing process
	Overlay welding	By welding, the process of depositing molten metal on the surface of the workpiece to form a welding layer is called sufacing welding.	Wear-resistant alloy weld ovwrlay
Vacuum method	Physical vapor deposition(PVD)	Under vacuum conditions, the metal is vaporized into atoms or molecules or ionized into ions and directly deposited on the surface of the workpiece to form a coating. The process is called physical vapor deposition coating, and the deposition particle beam comes from non-chemical factors.	Evaporative plating, Sputtering plating, Ion plating, TIN, TiCN plating, CrN, D-AC/TiNF, TiIN, D-AICrN, D-CR/CrAIN, D-AL/AITiN, D-AS/AISiN, D-AX/AIXiN, D-AO/AIFNM, D-ACX/AICiSi,D-DLC,DH-DLC.
	lon implantation process	The process of implanting different ions into the surface of a workpiece under high voltage to modify its surface is called ion implantation.	Boron injection
	Chemical vapor depostition CVD process	Uner low pressure ( sometimes also normal pressure), the process in which gaseous substances form solid deposition layers due to chemical reactions on the surface of the workpiece is called CVD coating.	CVD Silicon Oxide, Silicon Nitride CVD
Other methods	Painting	The process of applying paint (organic or inorganic) to the surface of the workpiece to form a coating by spraying or brushing is called coating.	spray paint, paint
	Strike plating	The process of forming a coating layer on the surface of the workpiece by the mechanical impact is called strike plating.	Impact galvanizing Copper strike plating Strike nickel plating
	Laser surface treatment	The process of irradiating the workpiece surface with a laser to change its structure is called laser surface treatment.	Laser quenching Laser remelting
	Ultra hard film technology	The technology of preparing a super hard film on the surface of the workpiece by a physical or chemical method is called super hard film technology.	Diamond films, Cubic boron nitride films
	Electrophoresis process	The workpiece is placed into the conductive water-soluble or water-emulsified paint as an electrode to form solution circuit with the other electrode in the paint. Under the action of the electric field, the coating solution has dissociated into charged resin ions, the cations move to the anode. These charged resin ions, along with adsorbed pigment particles, are electrophoresed to the surface of the workpiece to form a coating. This process is called electrophoresis.	Electrophoresis plating
	Electrostatic spraying	Under the action of DC high voltage electric field, the atomized negatively charged paint particles are directed to fly to the positively charged workpiece to obtain the paint film. The process is called electrostaitc spray painting.	Static paint spraying

The examples for surface finish chart

Surface-Treatment-Red bronze

Surface Treatment-Anodizing-of-aluminum-alloys