What Is Residual Stress in Metals?

Definition and Relationship Between Stress Relieving and Machining Deformation

Stress relieving is the process of reducing or eliminating residual stresses inside a material through heating or other techniques. During processing, especially when aluminum alloys undergo stretching, compression, or bending, internal stresses are generated. These stresses will affect the mechanical properties and stability of the material. By applying proper heating and holding, the stress relieving process effectively reduces these stresses, making the aluminum more stable.

Machining or processing deformation refers to the changes in shape and dimensions of aluminum alloys during manufacturing when they are subjected to external forces. Common methods include cold working and hot working. While these deformations help the material get the desired shape and size, they could also introduce residual stress.

The relationship between the two is that machining deformation introduces residual stress, while stress relieving is the means to eliminate this instability. Stress relieving ensures dimensional stability and long-term durability of aluminum alloys in service.

Why Does Residual Stress Happen?

Most residual stresses in metals, especially aluminum, come from the way the material is processed. When machining removes layers unevenly, the remaining part will lose balance and warp or twist, which is particularly common in large plates or thin-walled components. Heat-related processes such as welding or thermal treatment also contribute, since different areas of the metal heat up and cool at different rates, causing uneven shrinkage and stress buildup. In addition, as metals cool, structural phase changes occur, leading to expansion in some regions and contraction in others. These combined effects make residual stresses a natural byproduct of machining, heating, and cooling cycles, and they are especially evident in thick sections or materials like titanium that hold heat longer and cool less evenly.

What is the stress relieving process for Aluminium?

Stress relieving is a heat treatment process designed to reduce or eliminate residual stresses inside aluminum alloys. During machining or forming operations—such as stretching, bending, or compression—internal stresses are introduced into the material. These stresses can negatively affect dimensional stability and long-term performance. By applying controlled heating and holding the material at a specific temperature, stress relieving helps release these internal forces, making the aluminum more stable and reliable in service.

How to stress relieve 6061 aluminum?

6061 aluminum is one of the most widely used alloys in automotive parts, construction structures, and general machinery due to its excellent machinability and corrosion resistance. To ensure dimensional accuracy during cutting, welding, or forming, stress relief treatment is often performed. Typically, 6061 aluminum can be stress relieved by heating it to an appropriate aluminum stress relief temperature (commonly around 300–350 °C / 570–660 °F), holding it for a certain time, and then cooling it slowly. This process minimizes distortion during precision machining.

Should stress relief be done before or after machining?

Stress relieving can be applied either before or after machining, depending on the application. In most cases, stress relief is carried out before precision machining to release residual stresses from rolling, forging, or extrusion, ensuring that the workpiece does not warp during cutting. For high-precision aerospace or defense components, an additional stress relief cycle may be performed after rough machining but before final finishing, further reducing the risk of distortion in the final part.

Can you stress relieve 7075 aluminum?

Yes, 7075 aluminum, known for its exceptional strength and use in aerospace, defense, and high-load structural components, can also be stress relieved. Due to its higher hardness compared with 6061, 7075 is more prone to cracking or distortion if residual stresses are not properly managed. Stress relieving at controlled aluminum stress relief temperatures is crucial to maintain structural integrity, especially in demanding applications where mechanical stability is critical.

Aluminum stress relief temperature

The stress relief temperature for aluminum alloys generally ranges between 260–370 °C (500–700 °F), depending on the specific alloy and processing history. For example, 6061 is often treated near the lower end of this range, while high-strength alloys such as 7075 may require more precise temperature control to avoid over-aging or loss of mechanical properties. Proper control of temperature and holding time ensures that residual stresses are effectively reduced without compromising material strength.

What About Titanium?

Titanium is lightweight and strong, but also challenging to process because it easily develops residual stress during welding or forging. A common problem is weld cracking, which can occur if the weld cools unevenly or if residual stress is not properly relieved—sometimes even appearing later during service.

At Shenzhen Chinalco Metal, our titanium bars are treated to help reduce this problem, giving you a more stable and reliable material from the start.

In a word, residual stress in metals can be controlled or eliminated through several methods. One simple approach is natural aging, where the material is left in a stable environment for a period of time—often a few weeks—allowing aluminum, in particular, to gradually release stress on its own. A more controlled method is heat treatment, such as annealing or tempering, which uses elevated temperatures to help both aluminum and titanium alloys relieve internal stresses. Another technique is vibration stress relief, where the part is subjected to controlled vibrations that encourage the structure to relax. This method is commonly applied to large components such as machine bases, welded frames, or heavy equipment where thermal treatment may not be practical.

Shenzhen Chinalcometal offers high-quality aluminum and titanium materials that are carefully processed to reduce residual stress. If you are looking for high-quality aluminum alloys such as 6061 and 7075, or titanium bars and plates etc.  Leave us a message—we'll get back to you fast.