The quenched aluminum workpiece is reheated to an appropriate temperature lower than the lower critical temperature Ac1 (the starting temperature of pearlite to austenite transformation during heating), and the metal heat treatment is cooled in air or water, oil and other media after holding for a period of time craft. Or heat the quenched aluminum alloy workpiece to an appropriate temperature, hold it for a period of time, and then cool it slowly or rapidly. Generally used to reduce or eliminate internal stress in quenched steel, or reduce its hardness and strength to improve its ductility or toughness. The quenched aluminum workpiece should be tempered in time, and the required mechanical properties can be obtained through the combination of quenching and tempering.
The quenched aluminum workpiece is reheated to an appropriate temperature lower than the lower critical temperature Ac1 (the starting temperature of pearlite to austenite transformation during heating), and the metal heat treatment is cooled in air or water, oil and other media after holding for a period of time craft. Or heat the quenched aluminum alloy workpiece to an appropriate temperature, hold it for a period of time, and then cool it slowly or rapidly. It is generally used to reduce or eliminate internal stress in quenched steel parts, or to reduce its hardness and strength to improve its ductility or toughness. The quenched aluminum workpiece should be tempered in time, and the required mechanical properties can be obtained through the combination of quenching and tempering.
Tempering Process Of Aluminum
Tempering is a heat treatment process in which the workpiece is hardened and heated to a temperature below Ac1 (the starting temperature of pearlite to austenite transformation during heating), held for a certain period of time, and then cooled to room temperature. Tempering is generally followed by quenching, the purpose of which is to:
- (a) Eliminate the residual stress generated when the workpiece is quenched to prevent deformation and cracking;
- (b) Adjust the hardness, strength, plasticity and toughness of the workpiece to meet the performance requirements;
- (c) Stable organization and size to ensure accuracy;
- (d) Improve and enhance processability. Therefore, tempering is the last important process for the workpiece to obtain the desired properties. Through the combination of quenching and tempering, the required mechanical properties can be obtained.
According to the tempering temperature range, tempering can be divided into low temperature tempering, medium temperature tempering and high temperature Tempering Aluminum Extrusion.
The Temper Classification Of Aluminum
Low temperature tempering
- Tempering of workpiece at 150~250℃.
- The purpose is to maintain the high hardness and wear resistance of the quenched workpiece and reduce the quenching residual stress and brittleness
- Tempered martensite is obtained after tempering, which refers to the structure obtained when quenched martensite is tempered at low temperature. Mechanical properties: 58～64HRC, high hardness and wear resistance.
- Scope of application: Mainly used in various types of high carbon steel tools, cutting tools, measuring tools, molds, rolling bearings, carburized and surface quenched parts, etc.
Medium temperature tempering
- Tempering of workpieces between 350 and 500 °C.
- The purpose is to get higher elasticity and yield point, and proper toughness. After tempering, tempered troostite is obtained, which refers to the complex phase structure in which extremely fine spherical carbides (or cementite) are distributed in the ferrite matrix formed during martensite tempering.
- Mechanical properties: 35～50HRC, higher elastic limit, yield point and certain toughness.
- Application: Mainly used for springs, springs, forging dies, impact tools, etc.
High temperature tempering
- Tempering of workpiece above 500~650℃.
- The purpose is to obtain comprehensive mechanical properties with good strength, plasticity and toughness.
- Tempered sorbite is obtained after tempering, which refers to a complex structure in which fine spherical carbides (including cementite) are distributed in the ferrite matrix formed during martensite tempering.
- Mechanical properties: 25～35HRC, good comprehensive mechanical properties.
- Scope of application: Widely used in various important stress-bearing structural parts, such as connecting rods, bolts, gears and shaft parts.
- The composite heat treatment process in which the workpiece is quenched and tempered at high temperature is called quenching and tempering. Quenching and tempering is not only used for final heat treatment, but also for pre-heat treatment of some precision parts or induction hardened parts.
The Temper Of Aluminum Extrusion
Annealing is divided into recrystallization annealing, stress relief annealing spheroidizing annealing, and complete annealing according to different purposes. Normalizing is to heat the workpiece to a suitable temperature and then cool it in the air. The effect of normalizing is similar to that of annealing, but the obtained structure is finer. It is often used to improve the cutting performance of materials, and sometimes it is also used for some parts with low requirements final heat treatment.
Quenching is to rapidly cool the workpiece in a quenching medium of water, oil or other inorganic salts and organic aqueous solutions after heating and keeping it warm. After quenching, the material has an unbalanced structure, which is usually very hard and brittle. It needs to be kept at a temperature higher than room temperature for a long time and then cooled. This process is called tempering (aging). It can be seen from the above definition that whether it is annealing, normalizing, quenching or tempering, the workpiece must be heated, insulated and cooled during the heat treatment process. Therefore, in the heat treatment of aluminum profiles, the heating speed, holding time and cooling speed become the more important process parameters in the heat treatment process. Heat treatment of aluminum profiles is a process in which aluminum profiles are heated to a suitable temperature in a certain medium, and the articles and information on heat treatment of aluminum profiles are kept at this temperature for a certain period of time, and then cooled at different speeds.
Heat treatment of aluminum profiles is one of the more important processes in material production. Compared with other processing processes, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but changes the internal microstructure of the workpiece or changes the workpiece. The chemical composition of the surface that imparts or improves the performance of the workpiece. It is characterized by an improvement in the intrinsic quality of the workpiece, which is generally not visible to the naked eye. The “four fires” in the heat treatment of aluminum profiles refer to annealing, normalizing, quenching (solid solution) and tempering (aging). Among the “four fires”, quenching and tempering (aging) are closely related, and are often used together, and both are indispensable.
However, in actual production, in order to save costs and improve production efficiency, for products with low performance requirements, online quenching is often used instead of quenching furnace quenching, and natural aging is used instead of tempering. For example, when extruding low-alloyed alloy profiles such as 6060 and 6063, due to the low quenching sensitivity of these alloys, silicon and magnesium are rapidly dissolved above the solution temperature. Therefore, when the temperature at the outlet of the extruded material is guaranteed to be higher than the solid solution temperature, a supersaturated solid solution with a large solid solution degree can also be obtained by air-cooling quenching.
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