The surface treatment technology of die-casting die is required to be high. In recent years, various new surface treatment technologies of die-casting die are emerging, but in general, they can be divided into the following three categories:

1、 Improvement technology of traditional heat treatment process

2、 Surface modification technology, including surface heat diffusion treatment, surface transformation strengthening, electric spark strengthening technology, etc

3、 Coating technology, including chemical plating, etc

Improvement technology of traditional heat treatment process

The traditional heat treatment process of die casting die is quenching tempering, and the surface treatment technology has been developed. Due to the variety of materials that can be used as die-casting dies, the same surface treatment technology and process application in different materials will produce different effects.

Another development direction of heat treatment technology improvement is to combine traditional heat treatment technology with advanced surface treatment technology to improve the service life of die casting die.

For example, the combination of chemical heat treatment and NQN (carbonitriding quenching carbonitriding) combined with conventional quenching and tempering process can not only obtain higher surface hardness, but also increase the effective hardening depth, reasonable hardness gradient distribution, tempering stability and corrosion resistance, so as to achieve the same core performance of die casting die The surface quality and performance are greatly improved.

Surface improvement technology surface heat diffusion technology

The surface thermal diffusion technology includes carburizing, nitriding, boronizing, carbonitriding, sulfur carbonitriding and so on.

1. Carburizing and carbonitriding

The application of carburizing technology in cold, hot work and surface strengthening of plastic mould can improve the service life of mould. In the process of carburizing, the main processes are solid powder carburizing, gas carburizing, vacuum carburizing, ion carburizing and carbonitriding formed by adding nitrogen element in carburizing atmosphere.

Among them, vacuum carburizing and ion carburizing are the technologies developed in recent 20 years. This technology has the characteristics of fast carburizing speed, uniform carburizing layer, gentle carbon concentration gradient and small workpiece deformation. It will play an increasingly important role in the surface treatment of mold, especially in the surface treatment of precision mold.

2. Nitriding and related low temperature heat diffusion technology

This type includes nitriding, ion nitriding, carbonitriding, oxo nitriding, sulfo nitriding, and sulfo carbonitriding, oxo nitriding and sulfo sulphurizing.

These methods are simple, adaptable, low diffusion temperature (generally 480-600 ℃), small deformation of workpiece, especially suitable for surface strengthening of precision die, high hardness of nitriding layer, good wear resistance and good adhesion resistance.

3. Boronizing

Due to the high hardness (Feb: hv1800-2300, Fe2B: hv1300-1500), wear resistance and red hardness, as well as certain corrosion resistance and adhesion resistance, boronizing technology has achieved good application effect in mold industry.

However, due to the severe working conditions of the die-casting die, the boronizing process is seldom used in the surface treatment of the die-casting die. In recent years, there have been improved boronizing methods to solve the above problems, which can be applied to the surface treatment of the die-casting die.

Such as multi-component, coating powder infiltration, etc. The method of coating powder boronizing is to mix boron compound and other boronizing agents and then coat them on the surface of die-casting mould. After the liquid volatilizes, it is packed and sealed according to the general method of powder boronizing. It is heated at 920 ℃ and kept for 8h, then air-cooled.

The hardness, wear resistance and bending strength of the infiltrated layer on the die surface are all improved, and the service life of the die is increased by more than 2 times on average.

4. Rare earth surface strengthening

In recent years, the method of adding rare earth elements to die surface strengthening has been widely praised. This is because the rare earth element has many functions such as improving the penetration rate, strengthening the surface and purifying the surface. It has a great influence on improving the surface structure, physical, chemical and mechanical properties of the die. It can improve the penetration rate, strengthen the surface and generate rare earth compounds.

At the same time, it can eliminate the harmful effect of trace impurities distributed on the grain boundary and play the role of strengthening and stabilizing the grain boundary on the mold cavity surface. In addition, rare earth elements interact with harmful elements in steel to form high melting point compounds, which can inhibit the segregation of these harmful elements on the grain boundary and reduce the deep brittleness.

Adding rare earth elements into the surface strengthening treatment process of die-casting die can obviously improve the thickness and surface hardness of various infiltration methods, at the same time, make the microstructure of infiltration layer fine dispersion and hardness gradient decrease, so that the wear resistance, cold resistance and thermal fatigue resistance of die-casting die can be significantly improved, thus greatly improving the life of die-casting die.

At present, the surface treatment methods used in die casting die cavity are: rare earth carbonitriding, rare earth carbonitriding, rare earth boronizing, rare earth boroaluminizing, rare earth soft nitriding, rare earth sulfocarbonizing, etc.

Laser surface treatment

Laser surface treatment is to use laser beam to heat the surface of the workpiece and melt a certain depth of thin layer rapidly. At the same time, the alloy elements are coated on the surface of the workpiece by vacuum evaporation, electroplating, ion implantation and other methods. Under the laser irradiation, the alloy layer is fully integrated with the base metal. After cold setting, the alloy layer with a thickness of 10-1000 μ m with special properties is obtained on the surface of the mold. The cooling speed is Equivalent to quench.

For example, the surface of H13 die steel is treated by laser rapid melting process. The melting zone has high hardness, good thermal stability, high plastic deformation resistance, and obvious inhibition on the initiation and propagation of fatigue cracks.

Coating technology

As a kind of die strengthening technology, coating technology