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How to eliminate the residual stress of aluminum sheet!
Mar 11, 2018

Common methods for eliminating residual stress of aluminum sheet:


1. Prescription Elimination Act


The aging elimination method is a traditional method to reduce the residual stress of quenching. Because aluminum alloy materials, especially aerospace aluminum alloy materials are very sensitive to temperature, aging temperature increase, it is necessary to significantly reduce the strength index, so that MgZn2 and other strengthening phase precipitation too much, resulting in aging phenomenon. Therefore, the aging treatment after quenching is usually carried out under the lower temperature (less than 200-250 ℃), thus affecting the stress elimination effect (only 10-35%). Aluminum Plate semi-finished Products


2. Mechanical Tensile method


The principle of mechanical tensile method to eliminate stress is to apply a certain amount of permanent tensile plastic deformation to the quenched aluminum alloy sheet along the rolling direction, so that the plastic deformation occurs when the tensile stress is superimposed with the original quenching residual stress, so that the residual stress can be eased and released. The results show that the mechanical tensile method can eliminate more than 90% residual stress. But this method is only suitable for the parts with simple shape, and the microstructure uniformity of the aluminum alloy sheet before stretching is more demanding, and is used in the aluminum processing factory.


3. Die Cold Pressing method


Die cold pressure method is in a special finishing die, through the strict control of limited cold shaping to eliminate the complex shape of aluminum alloy die forgings in the residual stress. In fact, "molded" this term is not accurate, because its main mechanism is to make aluminum alloy die forgings local materials are "stretching" or "compression" role. When the finishing die is pressed, the finishing punch is embedded into the drawing slope of the end face and the flange (rib) strip of the aluminum alloy die forgings, which actually makes the Web part of the die Forgings "stretching" effect. Therefore, the method is to adjust and not eliminate the overall stress level of the part, it makes the residual stress of some parts of the aluminum alloy die forgings released at the same time, it may make the residual stress of other parts increase. In addition, as the aluminum alloy die forgings have already existed very large residual stress, compression deformation of the general may cause cold hardening, crack and fracture, and the deformation is too small to eliminate the effect of stress, so the limitations of this method in the actual operation is difficult to accurately control the molding deformation.


4. Cryogenic treatment


Cryogenic treatment method is also called cold stabilization method, which can be divided into two kinds, which are deep cooling and hot-heat cycling. One of the deep cold hot method is to immerse the parts containing residual stress in the 196 ℃ of liquid nitrogen in the deep cold, wait for the internal and external temperature even after the rapid use of hot steam injection, through the hot and cold in the direction of the opposite thermal stress, to offset the original residual stress field. The research shows that under the condition of selecting suitable process parameters, the deep cooling and hot-heat method can reduce the residual stress of 20-84%. The greatest advantage of cryogenic treatment is that the strength, hardness, abrasion resistance and microstructure stability of the material can be improved (at least not reduced) while the residual stress is effectively eliminated. Because cryogenic treatment has no restriction on the size and shape of parts, it is suitable for die forgings and castings with complex shapes. Cryogenic treatment before cutting can obviously improve the deformation tendency of aluminum alloy during processing, and improve the microstructure and stability of the material. However, the existing research indicates that cryogenic treatment can only eliminate the residual stress caused by temperature gradient, but it can not effectively eliminate the residual stress caused by uneven plastic deformation such as machining and cold forming, and the elimination effect of welding residual stress is poor. Aluminum Chute


5. Vibration elimination method


The principle of vibration elimination residual stress method is to use a portable powerful vibrator to make the metal structure produce one or more vibrationstates, so as to produce elastic deformation as mechanical loading, so that the residual stress in some parts of the part is superimposed upon the vibration load, which exceeds the material yield stress and causes plastic strain, Thus causing the reduction and redistribution of internal stress. The existing related research points out that when the aluminum alloy in the unstable state after quenching (0-2 hours), the best effect, residual stress can reduce the 50-70%, if the vibration after the quenching of 360 hours after the test, residual stress can only eliminate 10%-20%. The vibration eliminating stress (VSR) technology has the characteristics of high efficiency and energy saving, simple process and strong applicability, and it is a promising process for the parts without shape and size limitation, especially suitable for large and complex structure parts. In addition, after the vibration aging of the aluminum alloy members have good dimensional stability, in the subsequent machining process is not easy to produce deformation. At present, the mechanism of vibratory aging process is not enough, and the suitability of its application in aluminum alloy structural parts is disputed.


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