In order to reduce the weight, Formula 7 racing cars for college students are made of 7 series aluminum alloys (especially 7075 and 7050). 7075 aluminum alloy is a high-strength cold-treated forged alloy, far superior to low-carbon steel. 7075 is one of the most powerful commercial alloys. 7075 aluminum alloy has compact structure, strong corrosion resistance, good mechanical properties and strong anode reactivity. Fine grains make deep hole drilling performance better, tool wear resistance enhanced, and thread rolling more distinctive.

However, the surface hardness of aluminum alloy is low and it is not wear-resistant, which limits its application scope to some extent. By hard anodizing (anodizing) of aluminum alloy, a thin film with a certain thickness can be obtained, which can be used in aluminum transmission splines, bearing mounting positions, thread fastening positions and other parts. (Of course, the rules also require that aluminum alloy parts be anodized in some parts. Some people say there is no need to do or do something else, such as hard chromium plating. In fact, the advantages and necessity of anodic hardening are obvious. )

According to investigation and experiment, after anodic hardening of 7 series aluminum alloy, the thickness of oxide film can reach 30μm-50μm and the hardness is 50-55HRC, which can make aluminum material meet the requirements of spline. (The electrolyte is oxalic acid and DC, the electrolysis temperature is below 0℃, and the oxidation color is yellowish green with metallic luster-shit yellow).

Few factories can do this work, and the technical staff of this technical meeting are even rarer. Thanks to the efforts of our predecessors and teammates, we found a factory that oxidizes and exports pistons and nuclear power equipment, and finally successfully manufactured hard alumina splines. Let's talk about the specific steps and precautions.

Preparation before oxidation:

1, oxidation should be carried out before all finished products after processing are completed.

2. If possible, it is best to do metallographic analysis to confirm the authenticity of the materials, or ask the suppliers to provide a composition report (according to my investigation, Nanping Aluminum and Southwest Aluminum are still good, and this report will be provided on the bill of lading). The fake aluminum materials provided by some material suppliers are so confusing that the most perfect workpiece I made first is ablated (because the electrolyte ratio of different series of aluminum materials is different, two different series of materials will definitely be ablated when oxidized in the electrolytic cell).

Oxidation process:

1, first need pickling. It should be noted here that before pickling, we need to know whether we have done EDM, such as spline machining and wire cutting. If there is a machined surface, a hard oxide film will also be formed (whether alumina is not studied). Pickling must corrode this film, otherwise this part of non-conductive material will not adhere to the oxide film, but this will affect the surface smoothness and luster of the workpiece and make it black. In order to make the surface smooth and bright, and achieve the effect of drexler differential case, I polished it once with polishing blade and polishing wax, and the result is hehe. Later, I learned from experts that the machined surface of metal is physically smooth, that is, smooth concave-convex feeling, which will be exposed in oxidation. If you want a mirror effect, you can only get a mirror effect by chemical polishing, treating the machined surface with chemical reagents such as nitric acid, and then oxidizing it. Because this process will cause great pollution to the surrounding environment, it is rarely done, so Virgo's.

2. Pay attention to calculate the surface area of the workpiece, which is proportional to the current and oxalic acid content. Otherwise, there will be problems such as slow coating and thin film, which is of course related to electrolyte. Our factory can only make oxalic acid.

3. In the process of electrolysis, do not take out the membrane frequently to check its thickness, because if it is put into the oxidation tank again, it will not react.

4. Pay attention to the control current. If it is too large, it will be ablated; If it is too small, it will not respond.

5. After meeting the film thickness requirements, the color will be heavier after taking out. After washing, the luster will be good. When the water layer is dry, it will become dark. It should be a normal reaction. Just brightened it up.

6. Measure more points with a film thickness measuring instrument. I require the hardness of 50 threads to be above 50 degrees (1 thread, = 0.0 1mm = 10μ m). After a failure due to material reasons, the second time was a perfect success. To measure hardness, you can simply use a key. Keys will not leave scratches on them, but not before oxidation.

Be careful not to process aluminum splines after oxidation. The oxidized aluminum spline is more secure, the material is more limited, smaller and lighter. The total weight of the differential case I made is 0.9KG, and the Cusco differential 1 * * * weighs 2.5KG.

Attached is the physical and chemical composition of 7 series aluminum, which I hope you can use for metallographic experiment and analysis.

Physical properties of 7075 aluminum alloy;

Tensile strength: 524Mpa

0.2% yield strength: 455Mpa

Elongation: 1 1%

Elastic modulus e: 7 1gpa

Hardness: 150HB

Density: 2.8 1 g/cm3

Tensile strength σ b (MPa): ≥ 560

Elongation stress σ P0.2 (MPa): ≥ 495.

Elongation Δ 5 (%): ≥ 6

Chemical composition of 7075 aluminum alloy;

Silicon si: 0.40

Iron Fe: 0.50

Copper Cu: 1.2-2.0

Manganese Mn: 0.30

Magnesium mg: 2. 1-2.9

Chromium Cr: 0. 18-0.28

Zinc Zn: 5. 1-6. 1

Titanium: 0.20

Aluminium: allowance

Others: single: 0.05 Total: 0. 15

Chemical composition of 7050 aluminum alloy;

Aluminum balance

Chromium ≤0.04

Zirconium 0.08 ~ 0. 15

Zinc 5.7 ~ 6.7

Silicon (Si)≤0. 12

Iron 0.000 ~ 0. 150

Manganese (Mn)≤0. 10

Magnesium (mg) 1.9 ~ 2.6

Titanium ≤0.06

2.0-2.6 copper

(The main metals in Series 2 and Series 7 are distinguished by zinc and magnesium, and the contents of copper and zinc are distinguished between Series 7).

6063 aluminum alloy

T 1 treated yield strength: 90MPa, hardness: 42HB.

Yield strength of T5 treatment: 175MPa, hardness: 60HB.

Yield strength of T6 treatment: 2 10MPa, hardness: 73HB.

Yield strength of T832 treatment: 240MPa, hardness: 95HB.

The strength of 10HW is about 120MPa, and that of 13HW is about 270MPa. The strength corresponding to this HW is extrapolated, so it can only be used as a reference.