According to the failure mode of aluminum alloy die casting molds, PVD coating is a very good protection method for it. The following table shows the protective effect of PVD coatings on aluminum alloy die-casting molds.
Chromium has anti-adhesive properties and it is a good barrier to aluminum permeability. CrN
coating has wonderful high temperature resistance (about 800 °C), corrosion resistance and
nitriding resistance, and it is also has good welding resistance to non-ferrous metal.
As the TiAlN coating contains aluminum, the coating not only has high temperature oxidation
resistance(about 800°C), but also can provide optimum protection to the processing tool under
dry or high speed conditions. In addition, due to poor heat conductivity, aluminum die casting
can hinder heat conduction to the mold material, so it can prevent cracks in the mold.
TiN coating has good high temperature resistance (about 600 °C), corrosion resistance and
wear resistance, but the protection for molds is not as good as other coatings.
AlCrN coating has the advantages of oxidation resistance, high temperature resistance (about
1100 °C), wear resistance and high hardness. So it is very suitable for mold core, slider, insert,
insert pin and other molding parts, the performace is extremely good.
The method of surface coating is generally used to prevent the aluminum alloy's cracking of the die casting mold and greatly prolong the life of the mold. However, choose of the coating must follow some principles:
1. The coating can withstand high temperatures.
2. The coating has high chemical stability and it does not react with the aluminum alloy.
3. The coating is very dense and it can block the diffusion of A1 atom.
Among the surface coatings, CrN and AlCrN are the best choices. They can withstand 700 °C high temperature with high chemical inertness, also, these two coating are very dense to form a tight protective layer on the mold surface to prevent AI atoms from penetrating to the substrate.