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A7075 changes performance after stewing and the effect on the color of surface treatment

A7075 changes performance after stewing and the effect on the color of surface treatment

For a product that has a small batch production of customer A, the material processing of A7075 is selected, and the surface treatment of hard anodic oxidation is required. Due to the high precision requirements of the drawing, to ensure the accuracy of each precision Part, we adopted the stewing treatment to strengthen the performance of the material and ensure accuracy. Everything thought to be able to complete the product, but the problem came.

The product changed color after braising and surface treatment, so a sample was sent to the customer to observe the color difference. After receiving the sample, the customer feedback, not only the color has been changed, but also the performance of the product has been changed. The customer questions whether the material of A7075 is genuine, but we always insist on using the genuine material. Where is the problem? Because of the problems of color change and performance change, we conducted the following tests on the material of A7075 to confirm the influence of A7075 aluminum alloy on hard oxidation after stewed treatment.

Test 1: Stewing treatment — 10 hours of tempering at 200-220 using a tempering oven;

Judgment basis: hardness identification: whether the hardness of materials changes under different test conditions.

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Test 2: hard anodic oxidation — oxidation layer formed by plating on the surface of A7075.

Judgment basis: color recognition of surface treatment,

We selected 1PCS of aluminum alloy imported from Japan, model A7075 and specification 30*40*500 for testing. Divide the purchased raw material into two parts and number the material as no.1 and no.2.

Process of no.1 material: raw material of A7075 == rough machining == stewed processing == precision machining == electroplating;

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Process of no.2 material: raw material of A7075 == rough machining == precision machining == electroplating;

And then compare the hardness and surface treatment color of the two No. Material under different condition of processing, the results showed that:

1.No.2 without burning stew products after hard anodized color is OK, No.1 NG after burning stew;

2.No.1 products relative to the No.2 without burning stew, No.1 hardness falling by half;

Therefore, it can be judged by the test results:

  1. The product after stewing will have an impact on the hard oxidation treatment, resulting in the color of the surface treatment to be black and gray, judging NG

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  2. 2.The properties of A7075 material will change after stewed, which is similar to the hardness of the AL6061 series material. Do not conform to the characteristics of its material, judge NG.

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The conclusion can be obtained from the experiment: A7075 material will generate internal stress in the process of mechanical processing, to prevent stress deformation, the method of braising and tempering is adopted to remove the internal stress. Therefore, according to the results of this test, the material properties will be changed and the hardness will be greatly reduced after stewed. Therefore, it is not applicable. If the

processed material needs a surface treatment, the color is also an NG state. To sum up,  the stewed process for AL7075 cannot be used unless otherwise specified.

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