What is Aging Heat Treatment?

What is aging treatment?

Aging treatment refers to the solution treatment of metal or alloy workpieces (such as low carbon steel, etc.), after being quenched at high temperature or undergoing a certain degree of cold working deformation, it is placed at a higher temperature or room temperature to maintain its shape and size, and its performance changes over time. Varying heat treatment process. Generally speaking, after aging, the hardness and strength increase, while the plastic toughness and internal stress decrease. Steel with higher carbon content will obtain high hardness immediately after quenching, but its plasticity will become very low. After the aluminum alloy is quenched, the strength or hardness does not reach the peak immediately, and its plasticity not only does not decrease, but increases. After being placed at room temperature for a long time (for example, 4-6 days and nights), the strength and hardness of this quenched alloy increase significantly, while the plasticity decreases. The phenomenon that the strength and hardness of the quenched alloy change significantly with time is called aging. The aging at room temperature is called natural aging, and the aging at a certain temperature is called artificial aging. Aging treatment is to consciously store materials at room temperature or higher temperature for a longer period of time to produce an aging process.

Aging Heat Treatment History:

In order to eliminate the size and shape changes of precision measuring tools or molds and parts during long-term use, the workpiece is often reheated to 100-150°C after low-temperature tempering (low temperature tempering temperature 150-250°C) before finishing, and keep for 5 -20 hours, this kind of treatment to stabilize the quality of precision parts is called aging. It is particularly important to perform aging treatment on steel components under low temperature or dynamic load conditions to eliminate residual stress and stabilize steel structure and size. [1]

Aging treatment: refers to the heat treatment process in which the alloy workpiece is subjected to solution treatment, cold plastic deformation or casting, and after forging, it is placed at a higher temperature or at room temperature, and its performance, shape, and size change with time. If the aging treatment process of heating the workpiece to a higher temperature and performing aging treatment in a shorter period of time is used, it is called artificial aging treatment. The aging phenomenon that occurs when the workpiece is stored at room temperature or under natural conditions for a long time is called natural aging treatment. The third method is vibration aging, which has gradually entered the use stage since the early 1980s. Vibration aging treatment applies a certain frequency of vibration to the workpiece to release the internal stress without heating and is not as time-consuming as natural aging. To achieve the purpose of time limitation. The purpose of aging treatment is to eliminate the internal stress of the workpiece, stabilize the structure and size, and improve the mechanical properties.

In mechanical production, in order to stabilize the size of castings, castings are often placed at room temperature for a long time before cutting. This measure is also known as statute of limitations. But this aging does not belong to the metal heat treatment process.

In the early 20th century, when German engineer A. Wilm studied duralumin, he found that the hardness of this alloy was not high after quenching, but after a period of time at room temperature, the hardness increased significantly. This phenomenon was later called precipitation hardening. This discovery has generated great interest in the engineering community. Later, people successively discovered some aluminum alloys, copper alloys and iron-based alloys that can be strengthened by aging treatment, and created a new strengthening method that is essentially different from general steel quenching strengthening-aging strengthening.

Aging Heat Treatment Technique:

In most age-strengthened alloys, the original structure is composed of a solid solution and some metal compounds. The solubility of solid solutions increases with increasing temperature. Quenching before aging treatment is to dissolve as much solute as possible into the solid solution during heating, and although the solubility decreases during rapid cooling, the excess solute has no time to be analyzed from the solid solution, forming a supersaturated solid solution. Quenching for this purpose is often referred to as solution heat treatment.

After long-term repeated research, it has been confirmed that the essence of aging strengthening is to precipitate many very fine precipitate particles from the supersaturated solid solution (usually metal compounds, or the solute atoms in the supersaturated solid solution may gather in many small areas), forming some volume A very small solute-atom-enriched region.

When solid solution treatment is performed before aging treatment, the heating temperature must be strictly controlled so that the solute atoms can be dissolved into the solid solution to the maximum extent without causing the alloy to melt. The allowable deviation of heating temperature for solution treatment of many aluminum alloys is only about 5°C. For artificial aging treatment, the heating temperature and holding time must be strictly controlled in order to obtain an ideal strengthening effect. Sometimes segmented aging is used in production, that is, first keep warm for a period of time at room temperature or a temperature slightly higher than room temperature, and then keep warm for a period of time at a higher temperature. Doing so sometimes yields better results.

When maraging steel is quenched, it undergoes a structural transformation to form martensite. Martensite is a supersaturated solid solution. This steel can also be strengthened by aging treatment.

When low carbon steel is plastically deformed in a cold state and placed at room temperature for a long time, the strength increases and the plasticity decreases. This phenomenon is called mechanical aging.

What is natural aging process in heat treatment?

Natural aging is a step in the heat treatment of aluminum alloys in which the metal is removed from the quench bath and allowed to gain its full strength at room temperature. In artificial aging, the metal is held at an elevated temperature for it to gain its full strength in a shorter period of time.

What is natural aging process in heat treatment?

Natural aging is a step in the heat treatment of aluminum alloys in which the metal is removed from the quench bath and allowed to gain its full strength at room temperature. In artificial aging, the metal is held at an elevated temperature for it to gain its full strength in a shorter period of time

What is natural aging process in heat treatment?

Natural aging is a step in the heat treatment of aluminum alloys in which the metal is removed from the quench bath and allowed to gain its full strength at room temperature. In artificial aging, the metal is held at an elevated temperature for it to gain its full strength in a shorter period of time

What is two step aging heat treatment?

In the two step aging process, initially the temperature is increased to a certain T1 value, maintained at this temperature for a certain time period t1 and then temperature is lowered to T2 and maintained for another time period t2, after which the samples are allowed to cool back to the room temperature.

 What is ageing hardening process?

Age hardening creates changes in physical and mechanical properties by producing fine particles of a precipitate phase, which impede the movement of dislocations, or defects in a crystal’s lattice. Since dislocations are often the dominant carriers of plasticity, this serves to harden the material.

What is the difference between aging and quenching?

Quenching: Second, the metal is cooled rapidly. This generates a supersaturated solution. Aging: Third, the temperature is raised again to an intermediate level, to stimulate precipitation. This temperature must be maintained for several hours to complete the process.

What is aging temperature?

A temperature should be selected that provides a compromise between high strength and short ageing time. In the production of aluminium aircraft structures, the ageing temperature is usually in the range of 150–200 °C, which provides a good balance between strength and process time.

What are the 3 stages of heat treatment process?

• Heating – First stage in which any structure of an alloy is heated at a specific temperature. …
• Soaking – A second stage in which the heated metal completely changes its structure due to soaking. …
• Cooling – The third stage is cooling where the structure of the soaked metal is cooled either by quenching or by still air.