7 Series Aluminum Oxidation Methods and Precautions

[Chinese aluminum industry network] seven series of aluminum alloy oxidation: In order to reduce the use of light-weight material 7 Series aluminum alloy materials (especially 7075 and 7050 mainly), 7075 aluminum alloy is a cold forging alloy, high strength Far better than mild steel. 7075 is one of the more powerful commercial alloys. 7075 aluminum alloy structure, corrosion resistance, good mechanical properties and anode reaction. Fine grain makes for deeper drilling performance, enhanced tool wear resistance, and exceptional thread rolling.

However, the aluminum alloy has a low surface hardness and is not wear resistant. Its application range is subject to certain restrictions. When the aluminum alloy is hard anodized (anodic hardening), a film with good bonding strength to the substrate and a certain thickness can be used. Aluminum drive splines, bearing mounting locations, threaded fastening locations. (Of course, the rule also made anode hardening requirements for some parts of aluminum alloys. Some people said that they did not need to do or do other things such as hard chrome plating. In fact, the practicality and functional advantages and necessity of anode hardening are necessary. Sex is still obvious)

According to my investigation and experiment, after the 7-series aluminum alloy has finished anodizing, the thickness of the oxide film can be 30μm-50μm and the hardness is 50-55HRC, which can make the aluminum material meet the spline requirements. (Electrolyte is oxalic acid, direct current, electrolysis temperature is below 0 degree, oxidation color is yellowish green with metallic luster - yellowish yellow). There are few factories that can do this work. The technical staff of this technical meeting is even rarer. The younger brother is not talented. Under the efforts of his predecessors and teammates, he found a company that exports oxygen to pistons and nuclear power equipment. Successfully made hard aluminum oxide splines, which are not many twists and turns, talk about the specific steps and precautions.

Preparation before oxidation:

1, Oxidation should be completed before all the finished products after machining. 2. It is better to do some metallographic analysis to determine whether the material is true or false, or to allow suppliers to provide composition reports. (According to my research, domestic southwest aluminum is still a good, The report will be provided on this report.) The false aluminum material pit provided by some material suppliers to cry, the composition is not clear, and it abrogated the perfect machining part that I made by the previous one (because of different series of aluminum electrolyte ratio Different, and the oxidation of two different series of materials in an electrolytic cell will certainly happen ablation)

Oxidation process:

1, first pickling, here to note that before pickling must understand before doing the discharge class did not do processing, for example, EDM processing splines, wire cutting, etc., if there is a layer of processing the surface will form a layer Hard oxide film (not aluminum oxide has not been studied), pickling the film must be etched away, otherwise this part of the non-conductive will not be attached to the oxide film, but this will affect the surface smoothness and brightness of the workpiece, Make the workpiece dark. In order to make the surface smooth and bright, to achieve the effect of the Drexler differential shell, I polished with polished polishing wax and polished wax once, but the result was huh, and later learned with experts, the metal processing surface is a physical formation, that is The sensation of unevenness will be exposed during oxidation. The mirror effect can only be obtained through chemical polishing. The surface treatment with nitric acid and other chemical reagents will result in a mirror effect because the process will pollute the surrounding environment. Big, rarely done, so a Virgo friend can try.

2, pay attention to calculate the surface area of ​​the workpiece, which will have a certain proportional relationship with the current, as well as oxalic acid content, otherwise there will be slow film, thin film and other issues, of course, have a certain relationship with the electrolyte, I Edge manufacturers can only do oxalic acid 3, do not frequently remove the thickness of the viewing membrane during the electrolysis process, there will be the problem of re-into the oxidation pool does not respond to 4, pay attention to control the current, over the general ablation, too small does not respond 5, After the film thickness is reached, the color will be heavier after being removed. After washing with water, the gloss will be very good. After the water layer is dry, it will become dark. It should be a normal reaction. Just make it bright. 6. Measure the thickness of the instrument. At one point, I demanded that 50 wire hardness be more than 50 degrees (1 wire, = 0.01 mm = 10 micrometers), which was the second perfect success after the material failed once. Measuring the hardness, simple point can use the key, the key will not leave scratches on the top, before oxidation is otherwise.

Note that after oxidation, try not to reprocess it. The aluminum splines are more reliable after oxidation, and the material is more extreme, smaller and lighter. The total weight of the differential case I made is 0.9KG, plus CUSCO differential. The total weight of 2.5KG. I am incapable of cultivating ugliness with these simple knowledge. However, if I have any experience, I would like to refer to the physical and chemical components of 7-series aluminum. I hope you will do metallographic experiments and analysis. Can be used to get physical properties of 7075 aluminum alloy:

Tensile strength: 524Mpa

0.2% yield strength: 455Mpa

Elongation: 11%

Elastic Modulus E: 71GPa

Hardness: 150HB

Density: 2.81g/cm^3

Tensile strength σb (MPa): ≥560

Elongation stress σp0.2 (MPa): ≥495

Elongation δ5(%): ≥6

7075 aluminum alloy chemical composition:

Silicon Si: 0.40

Iron Fe:0.50

Copper Cu: 1.2-2.0

Manganese Mn: 0.30

Magnesium Mg: 2.1-2.9

Chrome Cr: 0.18-0.28

Zinc Zn:5.1-6.1

Titanium Ti: 0.20

Aluminum Al: Balance Others:

Single: 0.05

Total: 0.15

7050 aluminum alloy chemical composition:

Aluminum (Al) balance chromium (Cr) ≤ 0.04

Zr 0.08 to 0.15

Zinc (Zn) 5.7 to 6.7

Silicon (Si) ≤ 0.12

Iron (Fe) 0.000 ~ 0.150

Manganese (Mn) ≤ 0.10

Magnesium (Mg) 1.9~2.6

Titanium (Ti) ≤ 0.06

Copper (Cu) 2.0 to 2.6

(Distinguish between the main metals of 2 and 7 series see zinc and magnesium, and between 7 series to see the content of copper and zinc)

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