The role of aluminum heat treatment is to improve the mechanical properties of materials, eliminate residual stress and improve the machinability of metals. According to different purposes of heat treatment, the processes can be divided into two categories: preheat treatment and final heat treatment.
The purpose of preheat treatment is to improve processing performance, eliminate internal stress and prepare a good metallographic structure for final heat treatment. Its heat treatment process includes annealing, normalizing, aging, quenching and tempering and so on.
1) Annealing and normalizing
Annealing and normalizing are used for hot-worked aluminum blank material. Carbon steel and alloy steel with a carbon content greater than 0.5% are often annealed in order to reduce their hardness and easy to cut; carbon steel and alloy steel with a carbon content of less than 0.5% are used to avoid sticking to the knife when the hardness is too low. And use normalizing treatment. Annealing and normalizing can still refine the grain and uniform structure, and prepare for the subsequent heat treatment. Annealing and normalizing are usually arranged after the blank is manufactured and before rough machining.
2) Aging treatment
Aging treatment is mainly used to eliminate the internal stress generated in blank manufacturing and machining.
In order to avoid excessive transportation workload, for parts with general precision, it is sufficient to arrange one aging treatment before finishing. However, for parts with high precision requirements, such as the box of the jig boring machine, etc., two or several aging treatment procedures should be arranged. Simple parts generally do not need aging treatment.
In addition to castings, for some precision parts with poor rigidity, such as precision screw, in order to eliminate the internal stress generated during processing and stabilize the processing accuracy of parts, multiple aging treatments are often arranged between rough machining and semi-finishing. For some shaft parts, aging treatment should also be arranged after the straightening process.
3) Quenching and tempering
quenching and tempering refers to high temperature tempering after quenching. It can obtain a uniform and tempered sorbite structure, which is a preparation for reducing deformation during surface quenching and nitriding treatment. Therefore, quenching and tempering can also be used as a preheat treatment.
Due to the better comprehensive mechanical properties of the quenching and tempering parts, it can also be used as the final heat treatment process for some parts that do not require high hardness and wear resistance.
The purpose of final heat treatment is to improve mechanical properties such as hardness, wear resistance and strength. Its heat treatment process includes quenching, carburizing and quenching, and nitriding treatment.
1) Quenching
Quenching is divided into surface quenching and overall quenching. Among them, surface quenching is widely used because of its small deformation, oxidation and decarburization, and surface quenching also has the advantages of high external strength and good wear resistance, while maintaining good internal toughness and strong impact resistance. In order to improve the mechanical properties of surface quenching parts, heat treatment such as quenching and tempering or normalizing is often required as a pre heat treatment. Its general process route is: blanking, forging, normalizing, annealing, rough machining, quenching and tempering, semi-finishing, surface quenching, finishing.
2) Carburizing and quenching
Carburizing and quenching is to increase the carbon content of the surface layer of the part first, and after quenching, the surface layer obtains high hardness, while the core part still maintains a certain strength and high toughness and plasticity. Carburizing is divided into overall carburizing and partial carburizing. When partial carburizing is performed, anti-seepage measures should be taken for non-carburizing parts. Since the carburizing and quenching caused large deformation, and the carburizing depth is generally between 0.5 and 2 mm, the carburizing process is generally arranged between semi-finishing and finishing.
The process route is generally: blanking, forging, normalizing, rough machining, semi-finishing, carburizing and quenching, finishing. When the non-carburized part of the carburizing and quenching part adopts the process plan of removing the excess carburized layer after increasing the margin, the process of removing the excess carburized layer should be arranged after carburizing and quenching, before quenching.
3) Nitriding treatment
Nitriding is the process of infiltrating nitrogen atoms into a metal surface to obtain a layer of nitrogen-containing compounds. The nitriding layer can improve the hardness, wear resistance, fatigue strength and corrosion resistance of the surface of the part. Since the nitriding treatment temperature is low, the deformation is small, and the nitriding layer is thin, generally no more than 0.6~0.7mm, the nitriding process should be arranged as late as possible. In order to reduce the deformation during nitriding, it generally takes High temperature tempering for stress relief.
Edited by May Jiang from MAT Alumin
Post time: Sep-04-2023
