Nitriding Process - Improve the life of aluminum extrusion die

1. Nitriding process of aluminum extrusion die

The main process parameters of gas soft nitriding are nitriding temperature, nitriding time and nitriding atmosphere.

For aluminum profiles, we recommend the following nitriding process as follows:

Charging - preheating - nitriding - deep treatment - cleaning - polishing oiling

The mold should be cleaned before loading, and iron filings, aluminum and other materials can not be brought into the furnace. Preheating time should not be too long, control in 20-30 minutes, temperature control in 300 ~ 400℃. After preheating, the basket together with the mold shall be hung into the nitriding furnace. Before that, the salt bath in the nitriding furnace shall be fully melted and stirred evenly, and the salt temperature shall be controlled between 570 and 580°C. 

After the mold is placed, a certain amount of air is injected into the nitride salt bath, and the air volume is usually 6-12L/min. Heat ammonia to 500-600 ℃ for thermal decomposition :2NH3≒2[N]+3H2. Decomposition activity [N] atoms are absorbed by the surface of the steel and diffused into the metal, first dissolved in α-Fe to form a solid solution, and gradually formed nitride layer after saturation. Nitriding layer has the characteristics of high hardness, high wear resistance, high fatigue strength, high corrosion resistance and small heat treatment distortion, and is widely used in die manufacturing industry. After nitriding treatment, the service life of the die can be doubled or even increased several times.

The holding time is 3 hours and 20 minutes. Because the hardness of compound layer reaches the highest at 2-3 hours of co-infiltration, the depth of nitride layer increases slowly with the extension of time. The nitriding atmosphere is determined by the decomposition rate of ammonia gas and the drop rate of carburizing agent. After the completion of nitriding, the mold is hoisted out and put into the deep treatment furnace for treatment. The salt bath temperature in the deep treatment furnace is controlled between 320-340~C, and the processing time of the mold is controlled within 3-10 minutes. When the mold temperature is high and the mold enters the deep processing furnace, the salt bath temperature will rise to more than 400℃, at this time, a large number of bubbles will be generated, so pay attention to prevent the salt bath foam overflow. After the completion of the process, the mould is suspended into the deep treatment furnace and into the water tank for cleaning.

2.How often does the aluminum extrusion die nitriding?

The number of extrusions can be increased per nitriding.

Determine the nitriding time according to the size of the mold, the wall thickness of the profile, the complexity, etc.:

The first nitride is about 20-40 rods

The second nitride 30 to 60 rods.

The third nitride 45 to 80 rods