Die Casting Surface Finishes: The Complete Guide

surface finishes

This article lists all the questions and answers about die casting surface finishes. They will help you to understand the definition of surface finishes. The die casting surface finishes methods, what you should notice when you did the die casting finishes, etc. So, before you choose the die casting parts surface finishes, read this guide.

Table of Contents

What is die casting surface finishing?

Surface finishing is the process of artificially forming a surface layer on the surface of a substrate material with mechanical, physical and chemical properties different from those of the substrate. The surface finishing aims to meet the product’s corrosion resistance, wear resistance, decorative or other special functional requirements.

For metal castings, our more common  surface finishing methods are mechanical polishing, chemical treatment, surface heat treatment, and spraying surface; surface treatment is to clean, sweep, deburr, de-oil and de-oxidize the surface of the workpiece.

The workpiece in the process of processing, transportation, storage, etc., the surface is often with oxidation, rust mould residues of sand, welding slag, dust, oil and other dirt. To combine the deep layer can be firmly attached to the surface of the workpiece, must clean the surface of the workpiece before painting. Otherwise, it not only affects the bonding force of the coating and metal and corrosion resistance but also makes the base metal, even with the coating protection can continue to rust so that the coating peels off, affecting the mechanical properties of the workpiece and service life. Therefore, the surface treatment of the workpiece before painting is an important guarantee and measure to obtain a good-quality protective layer and prolong the product’s service life.

When doing the surface finishing of die casting, what points that need attention?

1、No oil and moisture

2、No rust and oxide

3、No adhesive impurities

4、No acid and alkali residues

5、The surface of the workpiece has a certain degree of roughness

How many types of common surface treatment methods are there?

Manual treatment.
Scrapers, wire brushes or grinding wheels, etc. Manual can remove the rust and oxide skin on the surface of the workpiece, but manual treatment is labour-intensive, low productivity, poor quality, and incomplete cleaning.

Chemical treatment.
Mainly the use of the acidic or alkaline solution and the surface of the workpiece oxides and oil chemical reaction, so that it dissolves in acidic or alkaline solution, to remove the surface of the workpiece rust oxide and oil, and then use the brush roller made of nylon or 304 # stainless steel wire (acid and alkali resistant solution made of steel wire brush roller clean will be able to achieve the purpose.

Casting oxidation

Mechanical treatment method.
Including the wire brush roller polishing, shot blasting method and shot blasting method. The polishing method is the brush roll driven by the motor, with the opposite direction of the movement of the roll in the upper and lower surface of the strip high-speed rotation brush to remove iron oxide. The brushed iron oxide is flushed out using a closed cycle cooling water flushing system. Shot blasting is a cleaning method using centrifugal force to accelerate the projectile and project it to the workpiece for rust removal.

Shot blasting is divided into shot blasting and sandblasting.
Surface treatment with shot blasting has a high striking force and noticeable cleaning effect. But shot blasting on thin plate workpiece, easy to make the workpiece deformation. Steel shot strikes the surface of the workpiece (whether shot blasting or shot blasting) to make the metal substrate deformation, due to Fe304 and FE203 no plasticity, broken peel, and oil film with its material deformation, so the workpiece with oil shot blasting, shot blasting can not altogether remove the oil.

Spraying (paint, powder)

The surface finishes techniques can be divided into the following categories depending on the method used

I. Electrochemical method
This method uses electrode reactions to form a coating on the surface of the workpiece. Among the primary methods are
(i) Electroplating
In an electrolyte solution, the workpiece is the cathode, and the process of forming a coating on its surface under the action of external current is called electroplating. Plating can be metals, alloys, semiconductors or solid particles containing various types, such as copper plating, nickel plating, etc.
(ii) Oxidation

In the electrolyte solution, the workpiece is the anode, under the action of the external current, so that the surface of the formation of the oxide film layer, called anodic oxidation, such as the anodic oxidation of aluminium alloy. Chemical or electrochemical methods can do the oxidation of steel. The chemical method is to put the workpiece into the oxidation solution and rely on the chemical action to form an oxide film on the surface of the workpiece, such as the bluing treatment of steel.

die-cast aluminum anode product

II. Chemical method
This method is without current action and uses chemical substance interactions to form a coating layer on the surface of the workpiece. Among the primary methods are
(i) Chemical conversion film treatment
In the electrolyte solution, the metal workpiece in no current external action, by the interaction of chemical substances in the solution and the workpiece to form a coating layer on its surface, known as a chemical transformation film treatment. Such as metal surface bluing, phosphating, passivation, chromium salt treatment, etc.
(ii) Chemical plating
In the electrolyte solution, the surface of the workpiece is catalytically treated without the action of an external current. The process of depositing certain substances on the surface of the workpiece to form a coating due to the reduction of chemical substances in the solution is called chemical plating, such as chemical nickel plating, chemical copper plating, etc.

decorated chrome plating

(III)Thermal processing method
This method is to melt or thermally diffuse the material under high-temperature conditions to form a coating on the surface of the workpiece. Its main methods are
(A) Hot dip plating
Metal workpiece into the molten metal, so that the surface of the formation of the coating process, called hot dip plating, such as hot dip galvanizing, hot aluminium plating, etc.
(B) Thermal spraying
The molten metal atomization is sprayed on the surface of the workpiece to form a coating process known as thermal sprayings, such as thermal spraying zinc and thermal spraying aluminium.
(C) thermal stamping
The process of heating and pressurizing 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, etc.
(D) chemical heat treatment
Workpiece contact with chemical substances, heating, in the high-temperature state ordered a specific element into the workpiece surface process, known as chemical heat treatment, such as nitriding, carburizing, etc.
(E) overlay welding
To weld so that the molten metal is set on the surface of the workpiece and the formation of the welding layer process, known as overlay welding, such as overlay welding wear-resistant alloys.

IV. Vacuum method
This method is the process of forming a coating by vaporizing or ionizing the material deposited on the surface of the workpiece under a high vacuum. Its primary methods are.

(i) Physical Vapor Deposition (PVD)
Under vacuum conditions, the process of vaporizing metal into atoms or molecules, or making it ionize into ions, and depositing it directly onto the surface of the workpiece to form a coating is called physical vapour deposition. Its deposited particle beam is derived from non-chemical factors, such as evaporation, sputtering, ion plating, etc.

(ii) ion injection

The process of injecting different ions into the surface of the workpiece at high voltage to modify its surface is called ion injection, such as boron injection, etc.

(iii) chemical vapour deposition (CVD)

Under low pressure (sometimes also at atmospheric pressure), gaseous substances on the workpiece surface due to chemical reactions to generate a solid deposition layer process, known as chemical vapour deposition, such as vapour deposition of silicon oxide, silicon nitride, etc.

V. Other methods
Mainly mechanical, chemical, electrochemical, and physical methods. The main methods among them are.
(A) painting
Idle spraying or brushing method, the process of coating (organic or inorganic) on the surface of the workpiece to form a coating, known as painting, such as spray paint, brush paint, etc.
(B) Impact plating
The process of forming a coating layer on the surface of the workpiece by the mechanical impact is called impact plating, such as impact galvanizing.
(C) Laser surface treatment
Laser irradiation of the surface of the workpiece so that the structure of the process of change, known as laser surface treatment, such as laser quenching, laser remelting, etc.
(D) Super Hard Film Technology
The technology of preparing a super hard film on the surface of the workpiece by physical or chemical methods is called super hard film technology. Such as diamond film, cubic boron nitride film, etc.
(E) Electrophoresis and electrostatic spraying
· Electrophoresis, the workpiece as an electrode into the conductive water-soluble or water-emulsified paint, and another electrode in the paint to form a solution circuit. Under the electric field, the paint solution has dissociated into charged resin ions. Cations move to the cathode, and 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 called electrophoresis.

· Electrostatic spraying, in the DC high voltage electric field effect, atomized negatively charged paint particles directed to fly to the workpiece connected to the positive charge, to obtain the process of the paint film, called static spraying. Edit this paragraph with another taxonomy.

· Common applications of wire brushes are cleaning castings, both ferrous and non-ferrous; cleaning spatters and slag in welding; and clearing dust, corrosion, and paint as long as the strength of the substrate material is sufficient to withstand the brushing. Wire brushes produce a beautiful surface and can also be used to create surfaces with decorative qualities.

surface finishing die casting products

How do we determine the level of cleanliness of die castings?

That is, cleanliness, there are two usual international standards: one is the United States in 85 years to develop “SSPC-“; the second is the Swedish 76 years to develop.
“Sa-“, divided into four grades, Sa1, Sa2, Sa2.5, and Sa3, for the international customary common standards, are as follows.
Sa1 level – equivalent to the U.S. SSPC-SP7 level. This is the lowest level of the four cleanliness using the general simple manual brush removal and abrasive cloth sanding method. The protection of the coating is only slightly better than the workpiece not using the treatment.
Technical standard for Sa1 level treatment: 

The surface of the workpiece should be free from visible dirt such as oil, grease, residual oxide, rust spots, paint, etc. Sa1 level is also called the manual brush-off cleaning level. (or sweeping grade)

Sa2 grade – equivalent to U.S. SSPC-SP6 grade. The technical standards for Sa2 level treatment: the surface of the workpiece should be free from visible grease, dirt, oxide, rust, paint, oxides, corrosion, and other foreign substances (except blemishes), but the blemishes are limited to no more than 33% of the surface per square meter and can Including slight shading; a small amount of minor discolouration caused by blemishes, rust; oxide and paint blemishes. If the original surface of the workpiece has dents, minor rust and paint will also remain at the bottom of the dents. sa2 grade is also called commodity cleanup grade (or industrial grade).

Sa2.5 grade – is commonly used in industry and can be used as the technical requirements and standards for acceptance. sa2.5 grade is also called the near-white cleaning grade (near-white or out-white grade). sa2.5 grade treatment technical standards: the same as the first half of the Sa2 requirements, but the defects are limited to no more than 5% of the surface per square meter and can include Slight dark shadows; a small amount of minor discolouration caused by blemishes and rust; oxide skin and paint blemishes.

Sa3 level – a level equivalent to the U.S. SSPC-SP5 level, is the highest level of treatment in the industry, also known as the white cleanup level (or white level) Sa3 level of treatment of technical standards: the same as Sa2.5 level but 5% of the shadow, blemishes, rust, etc. had to exist.

Comparison of international common surface treatment standards:



SIS 055900


ISO 8501

BS 7079

Solvent cleaning





Hand tool cleaning





Motorized tool cleaning





Combustion Cleaning





Sandblasting white metal





Sandblast Commercial Grade





General grade for sandblasting





Chemical Cleaning





Sandblast Near White Metal





Motorized Cleaning Bare Metal 





V1diecast offers professional surface finishes services

 If you are unsure which surface finishing is suitable for your project, please send your documents and talk to our engineers immediately. We will give you a detailed explanation and see which options are available to meet your project needs. Or you can see our surface finishing srevice in this page.

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