Metal products have long permeated every aspect of life—from faucets, doorknobs, and window frames in homes to molds and mechanical parts in industry, and aluminum alloy casings in electronic devices… However, metals inevitably face problems such as wear, rust, and corrosion during use. How can we extend their service life and ensure metal products “serve for a long time”? The answer lies in metal surface treatment technology. The core purpose of metal surface treatment is to improve the hardness, wear resistance, and corrosion resistance of metal surfaces through a series of processes, while optimizing the appearance and texture, ultimately improving product quality and extending service life. For core industrial components such as molds, appropriate surface treatment technology can increase lifespan by 5 to 10 times, or even dozens of times, resulting in significant economic benefits. Today, we'll guide you through six common metal surface treatment technologies, discussing their principles, characteristics, and application scenarios, while also examining the current status and future direction of mold surface treatment in China.

1. Current Status of Mold Surface Treatment in China

Currently, domestic mold manufacturing enterprises mainly rely on traditional surface quenching, carburizing/nitriding, electroplating, and chemical plating technologies. However, these technologies generally suffer from problems such as uneven surface hardness distribution and heat treatment deformation that are difficult to solve. As industry demands for mold precision and lifespan continue to increase, the application of new technologies has become an industry consensus. Surface coating technology, TD coating treatment technology, laser surface strengthening technology, and electron beam strengthening technology are gradually becoming key directions for enterprise technological transformation. These technologies can not only compensate for the shortcomings of traditional technologies but also achieve a leapfrog improvement in mold performance.

2. Six Common Metal Surface Treatment Technologies: A Comprehensive Guide

2.1 Quenching

Quenching is the most traditional heat treatment process for die-casting molds, with the core being "quenching-tempering." Later, it gradually combined with surface treatment technology, resulting in more efficient strengthening methods. Due to the wide variety of mold materials, the same surface treatment process can have vastly different effects on different materials. Therefore, the industry has proposed "substrate pretreatment technology"—customized processing techniques for different mold materials to improve mold performance and extend its lifespan. The more popular upgrade solution now is a composite strengthening approach combining "traditional processes + advanced surface treatments," such as NQN composite strengthening technology: combining chemical heat treatment carbonitriding with conventional quenching and tempering processes. This achieves both high surface hardness and increases the effective hardened layer depth, resulting in a more reasonable hardness gradient distribution in the infiltrated layer, while simultaneously improving tempering stability and corrosion resistance. In this way, the mold maintains good core performance while significantly improving surface quality and durability.

2.2 Metal Surface Brushing

The brushing process creates specific textures on the metal surface through mechanical friction. This removes surface scratches and serves a decorative purpose. Common textures include straight lines, random lines, threads, ripples, and swirls, catering to different decorative needs: Straight Line Brushing: Divided into continuous and discontinuous brushing. Continuous brushed finishes can be achieved by horizontally rubbing the aluminum plate surface with a scouring pad or stainless steel brush in a straight line. Changing the wire diameter adjusts the texture. Discontinuous brushed finishes are achieved on a polishing or texturing machine using two sets of differential rollers (upper set of fast grinding rollers + lower set of slow rubber rollers), creating fine, discontinuous straight lines as the metal plate passes over them. Random brushed finishes: Under a high-speed rotating copper wire brush, the aluminum plate is moved back and forth and side to side, creating an irregular, matte effect without obvious textures. This requires a high degree of surface finish. Wavy brushed finishes: On a polishing or texturing machine, the axial movement of the upper grinding rollers creates wavy patterns on the metal surface, resulting in a dynamic visual effect. Spiral brushed finishes (also known as swirl polishing): A cylindrical felt or nylon abrasive wheel is mounted on a drill press, and polishing paste mixed with kerosene is used to rotate and polish the metal plate surface, creating fine swirling brushed finishes. This is commonly used for round signs and small decorative dials. Threaded Finish: A small motor equipped with circular felt (at a 60-degree angle to the tabletop), along with a sliding plate with a fixing device (a polyester film on the sliding plate limits the thread width), creates a consistent thread pattern on the aluminum plate surface through the rotation of the felt and the linear movement of the sliding plate, resulting in a highly decorative effect.

2.3 Anodizing Coloring

Aluminum and aluminum alloys, as light metals, are widely used in electronic devices and household goods (for example, magnesium alloy casings account for over 50% of laptop casings, and Apple and Sony electronic products extensively use aluminum alloys). Anodizing coloring is the most common surface treatment process for these light metals—it enhances surface corrosion resistance and achieves rich decorative effects. A key point here is that coloring is not a post-oxidation treatment but rather occurs simultaneously with the oxidation process. The coloring effect is closely related to the aluminum alloy composition and process parameters. After anodizing coloring, there are usually subsequent treatments to refine the appearance. There are three common anodizing coloring methods:

2.3.1 Dye Adsorption Coloring

Anodized films achieve coloring through dye adsorption, offering a rich selection of colors to suit various decorative needs.

2.3.2 Self-Sparkling Anodizing Coloring

Specific aluminum materials spontaneously form colored anodic oxide films through electrolysis in a suitable electrolyte, eliminating the need for additional dyeing.

2.3.3 Electrolytic Coloring

Utilizing the pores in the oxide film, metals or metal oxides are electrodeposited onto the film, achieving coloring with high color durability and resistance to fading.

2.4 Diamond Engraving on Aluminum Plates

Diamond engraving on aluminum plates is a targeted surface treatment process. The treated aluminum plates offer numerous advantages: good compressive strength and hardness at low temperatures, high mechanical strength, wear resistance, lightweight, good dimensional stability (not easily deformed at high temperatures), excellent fire resistance, and a simple process with good gloss, easy coloring, and lower cost than other thermoplastics. Typical applications of this process include consumer electronics (such as mobile phone and tablet casings), toys, environmentally friendly products, automotive dashboards, door panels, and outdoor grilles, enhancing both product quality and performance.

2.5 Surface Electroplating

Electroplating is a classic surface finishing method. The principle is simple: in a solution containing the salt of the metal to be plated, the metal to be plated acts as the cathode. Through electrolysis, the metal cations in the solution are deposited on the substrate surface, forming a new coating—this coating has completely different properties from the substrate metal, achieving protective, decorative, or other special functions. The electroplating process typically consists of three steps: pretreatment before electroplating, electroplating, and post-plating treatment; none can be omitted. Based on their function, coatings can be divided into three categories:

2.5.1 Protective Coatings

The main function is rust and corrosion prevention, extending the service life of metals;

2.5.2 Decorative Coatings

Enhancing the gloss and aesthetics of metal surfaces, making products more attractive;

2.5.3 Functional Coatings

Imparting special properties to metals, such as conductivity, wear resistance, and high-temperature resistance.

2.6 Surface Sandblasting

Sandblasting is widely used in metal surface treatment. The principle is to use accelerated abrasive particles to impact the metal surface, achieving rust removal, deburring, oxide layer removal, or surface pretreatment, while simultaneously changing the surface finish and stress state. Key parameters affecting sandblasting effectiveness include: abrasive type, particle size, blasting distance, angle, and speed. Besides sandblasting, shot blasting is also a similarly efficient option. Sandblasting processes are mainly divided into two types: pneumatic shot blasting and impeller shot blasting. Their core advantages and application scenarios are as follows: Deburring and removing burrs: Excellent for removing burrs from die casting, stamping, flame cutting, and forging, especially suitable for thinner workpieces and burrs with pores; Surface cleaning: Removes residual sand particles from sand casting, rust stains on cast iron/steel parts, and oxide scale from heat treatment, welding, hot forging, and rolling; Coating pretreatment: Removes existing paint or protective layers, covers defects such as cracks and cold lines on the surface of castings, and provides a uniformly roughened surface for better adhesion of subsequent oiling and spraying; Surface strengthening: For high-stress metal parts such as springs and connecting rods, circular abrasives (such as stainless steel shot) are used in a high-energy shot blasting machine or a high-power sandblasting machine. Continuous impact causes deformation of the metal surface, achieving a strengthening effect. The method for judging the strengthening effect is simple: test the workpiece after treatment and measure whether the deformation meets the requirements.

3. Quick Overview of Core Application Scenarios of Different Surface Treatment Technologies

3.1. Quenching (including composite strengthening)

The core advantages are improved surface hardness and enhanced wear resistance, while significantly extending the service life of workpieces, making it particularly suitable for scenarios with extremely high requirements for strength and durability. Typical applications include die-casting molds, core components of mechanical transmissions, and other key industrial parts. After strengthening treatment, it can effectively cope with harsh working environments such as high-frequency friction and high-pressure impact, significantly reducing the wear rate.

3.2. Metal Surface Brushing

With strong decorative properties and the ability to repair minor surface scratches as its core advantages, it focuses on optimizing the appearance and texture of metals. It is commonly used in electronic product casings (such as mobile phone and laptop bezels), home hardware (faucets, door handles), decorative panels, and other products where aesthetics are important. Different brushed textures can adapt to various design styles, such as minimalist and sophisticated.

3.3 Anodizing Coloring

Combining excellent corrosion resistance and rich, long-lasting color performance, it is an ideal surface treatment solution for light metals. Primarily used in aluminum alloy and magnesium alloy products, such as electronic device housings, door and window frames, and home decorations. It protects light metals from oxidation and corrosion, while offering a variety of colors to meet personalized design needs, and the colors are resistant to fading and peeling.

3.4. Diamond Engraving on Aluminum Plates

The core advantages are high hardness and wear resistance, while maintaining aesthetics and controllable cost. After processing, it also possesses good dimensional stability and fire resistance. Typical applications include consumer electronics (phone and tablet housings), toys, environmentally friendly products, as well as automotive dashboards, door panels, and outdoor fencing, enhancing product quality and adapting to the wear and tear of daily use.

3.5. Surface Electroplating

Achieving a balance of protection, decoration, and functionality, it has a very wide range of applications. Protective coatings are commonly used on faucets, hardware accessories, and other easily rusted metal parts, providing rust and corrosion protection; decorative coatings enhance the gloss and aesthetics of jewelry and home decorations; functional coatings are used in molds, electronic components, etc., imparting special properties such as conductivity, high temperature resistance, and high wear resistance.

3.6. Surface Sandblasting

Its core function is to clean the surface, roughen it, and enhance its performance. It is a versatile pretreatment or repair process applicable to multiple scenarios. Common applications include surface pretreatment of mechanical parts before painting (enhancing coating adhesion), cleaning residual sand particles from castings, removing rust stains from steel, and removing oxide scale after heat treatment. It can also be used for surface strengthening of high-stress metal parts such as springs and connecting rods, improving the fatigue resistance of the workpiece through precise processing.

4. Summary

The core value of metal surface treatment technology lies in "achieving a dual improvement in metal performance and appearance at a relatively low cost"—whether it's small hardware in daily life or core molds in industry, appropriate surface treatment can double their service life and provide a better user experience. From a technology selection perspective: for those seeking decorative appeal and color diversity, brushed finish and anodizing are suitable options; for those needing to improve hardness and wear resistance, quenching and sandblasting are preferred; for those seeking a balance between protection and decoration, electroplating is a classic choice; and for lightweight metal products, anodizing and diamond engraving on aluminum plates are suitable. From an industry development perspective, while traditional surface treatment technologies are still widely used, they have unavoidable shortcomings. New technologies such as laser surface strengthening and TD coating are becoming key to addressing high-end demands. In the future, whether in industrial production or daily applications, metal surface treatment technology will develop towards greater efficiency, precision, environmental friendliness, and durability. Choosing the right surface treatment technology can not only prevent metal products from rusting and wearing out, but also enhance product quality and added value. Hopefully, this guide will help you find a suitable metal surface treatment solution, ensuring that every metal product offers excellent value for money and a long service life.