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1、铝铸件的抛光和氧化（Polishing and oxidation of aluminium castings）After light, the surface quality is already high enough to reach even specular light and has been passivated. No further treatment is required because of special customer requirements.Electrolytic polishing can further improve the surface quali
2、ty.Oxidation can improve corrosion resistance. Theres no need for shock rays.Dyeing can improve corrosion resistance and obtain the desired color. Theres no need for shock rays.Oxidation of aluminium castingsElectrochemical oxidation of metals or alloys. The metal or alloy parts are used as anodes,
3、and the oxide film is formed on the surface by electrolysis. The metal oxide film changes the surface state and properties, such as surface coloring, corrosion resistance, abrasion resistance and hardness, and metal surface protection. For aluminum castings, anodizing is often encountered, but it mu
4、st be said that the process of casting aluminum alloys is difficult to do, and profiles and pure aluminum are very good to do, which is related to the composition of its own alloy.A senior oxidation technology staff told me that the casting Aluminum Alloy also is not to say do not exactly anodic oxi
5、dation, is not good to do, the first is Aluminum Alloy alloy, various metal elements mixed, the conductivity of different quality and quantity of the oxide layer formed on the alloy surface is different. The number of oxide layer is different, it means that the different thickness, oxidation layer q
6、uality is different, it means that there is difference between the compact degree of oxide layer is the result of oxidation surface uneven thickness, and accompanied by flowers, the effect is very poor. But its not absolute. It can be remedied by technical means.The oxidation expert also mentioned t
7、hat casting aluminum alloy in different grades of aluminum anode oxidation is also difficult, in general, die-casting aluminum than casting aluminum difficult to oxidation. Because the melting flow of the aluminum is better than that of the casting aluminum, it is decided that the composition is sil
8、icon. The commonly used die cast aluminum A380 is between 7.5 and 9.5 silicon, while A356 is between 6.5 and 7.5. Some of the silicon content of die cast aluminum is even between 10% and twenty oh. The gap is still very large. Silicon is, as everyone knows, a semi conducting substance, and the doped
9、 silicon will make the oxidized surface of the cast aluminum alloy even more tear stained.What are the surface treatments made of die-casting aluminium for lamps?Analysis and prevention of anodic oxidation failure of aluminum alloyAbstract the paper introduces the frequently occurring failures in th
10、e anodizing process of aluminum alloy, analyzes the causes of the failures, and takes effective preventive measures to reduce the occurrence of failures and ensure their quality.0 PrefaceAnodic oxidation of aluminum is aluminum or Aluminum Alloy anode to lead as cathode in sulfuric acid, oxalic acid
11、, chromic acid and aqueous solution electrolysis, the surface oxide film. Among them sulfuric acid anodizing is the most widely used. Aluminum sulfate and Aluminum Alloy anodic oxidation film has high adsorption capacity, easy sealing alone L or coloring treatment, more improve the corrosion resista
12、nce and appearance. The thickness of anodic oxide film generally 3 15 m, the anodic oxidation process Aluminum Alloy sulfuric acid electrolyte has the advantages of simple operation, stable, cost is not high, the process is mature, but in sulfuric acid anodized process often unavoidable failure occu
13、rred, influence of oxide film quality. It is of important practical significance to improve the quality of Anodizing of aluminum alloy by careful summing up and analyzing the causes of the failures and taking effective preventive measures.1 common faults and analysis(1) Aluminum Alloy products by su
14、lfuric acid anodic oxidation, partial oxidation without touch, showing visible black spots or stripes, film drums tumor or cavity phenomenon. This kind of fault is rare, but it also happens.The cause of the failure is generally related to the composition, microstructure and phase uniformity of alumi
15、num and aluminum alloys, or to some metal ions or suspended impurities dissolved in the electrolyte. The chemical composition, microstructure and uniformity of metal phases affect the formation and properties of aluminum oxide and aluminum alloys. The oxide film of pure aluminum or aluminum magnesiu
16、m alloy is easy to generate, and the film quality is better. And aluminium silicon alloy or aluminium alloy with higher copper content,The oxide film is difficult to produce, and the resulting film is dark, gray and poor luster. If the surface of the metal phase is uneven, tissue segregation, micro
17、impurities segregation or improper heat treatment caused by uneven parts, etc., it is easy to produce selective oxidation or selective dissolution. If the segregation of silicon content in Aluminum Alloy local, are often caused no local or a black spots or stripes on the local selective dissolution
18、causes cavitation etc. In addition, if there are suspended impurities, dust or copper, iron and other metal impurities in the electrolyte, the ion content is too high, often make the oxidation film appear black spots or black stripes, affect the anti corrosion protection performance of the oxide fil
19、m.(2) the anodic oxidation parts with the same groove, some have no oxide film or thin or incomplete film layer, and some of them have the burning and melting phenomenon at the fixture and parts contact. Such failures often occur in the process of flow acid anodizing, and seriously affect the anodiz
20、ing quality of aluminum alloys.Because of the good insulation of the aluminum oxide film, the aluminum alloy parts must be firmly attached to the universal or special fixture before anodizing, so as to ensure good electrical conductivity. Copper or copper alloy materials should be used in the conduc
21、tive bar, and sufficient contact area should be guaranteed. Fixture and parts contact, both to ensure free passage of the current, but also as far as possible to reduce the fixture and parts of the contact mark. Contact area is too small, the current density is too large, will produce overheating, e
22、asy to burn parts and fixtures. No oxide film or film incomplete and so on, mainly due to the fixture and parts of bad contact, poor electrical conductivity, or because the fixture on the oxidation film is not completely removed.(3) after anodizing of aluminum alloy, the oxide film is loose, powder
23、and even touched by hand. Especially after sealing and filling, the surface of the workpiece has a severe powder layer, and the corrosion resistance is bad. This kind of breakdown often occurs in summer, especially, there is no sulfuric acid anode tank with cooling device. After 1-2 tank parts are t
24、reated, the phenomenon of loose powdering will appear, and the quality of oxide film is obviously affected.Because of the great resistance of anodic oxidation film of aluminum alloy, a large amount of Joule heat will be produced in the process of anodic oxidation. The higher the groove voltage is, t
25、he more heat will be generated, which will lead to the rising of electrolyte temperature. Therefore, in the anodic oxidation process, it is necessary to use mixing or cooling devices to keep the electrolyte temperature in a certain range. Under normal circumstances, the temperature should be control
26、led at 1326 degrees, the quality of the oxide film is better. If the electrolyte temperature exceeds 30 degrees, the oxide film will be loose, powdering, the film quality is poor, serious scorch phenomenon occurs. In addition, when the temperature is constant, the anodic current density must be limi
27、ted, because the anode current density is too high, the temperature rise sharply, oxide film is easy to loose powdery or granular, is very unfavorable to the film quality.(4) chance of anodic oxidation Aluminum Alloy after oxide film sometimes produces pitting, dim and dark, serious black spot of co
28、rrosion significantly, resulting in scrap parts, caused a great loss.Such failures often happen by accident and have special causes. In Aluminum Alloy anodizing process, half-way off again to electricity, tend to make the film during the blackout in dim and dark, parts cleaning tank to stay too long
29、, cleaning the sink acidity is too high, the water quality is clean, containing more suspended solids, mud and sand, often make Aluminum Alloy parts electrochemical corrosion, pitting corrosion occurred black. Sometimes add tap water to the electrolyte in water treatment, bleaching powder and Cl- co
30、ntent exceed the standard of dress or sometimes HCl containers are not thoroughly cleaned and containing sulfuric acid, will make the Cl- mixing excess anodizing electrolyte, resulting in parts of anodic oxidation Aluminum Alloy produce pitting end-of-life products etc.2 preventive measuresAluminum
31、Alloy sulfuric acid anodizing film quality, quality of corrosion protection performance mainly depends on the Aluminum Alloy composition, film thickness and process conditions of anodic oxidation, such as temperature, current density, water use and anodic oxidation after filling sealing process etc.
32、In order to reduce or avoid anodic oxidation failure and improve product quality, effective measures should be taken from the micro point of view.(1) for different aluminum alloy, such as casting molding, rolling forming or mechanical processing, molding or heat treatment welding process, according
33、to the actual situation, choose the appropriate pretreatment method. For example, cast aluminum alloy surface, its non machining surface should generally use sand blasting or shot blasting, in addition to the net of its original oxidation film, sand and so on. The aluminum alloy with high silicon co
34、ntent (especially cast aluminium) should be etched and activated by the nitric acid mixed acid solution containing about 5% hydrofluoric acid, so as to effectively maintain a good activation surface and ensure the quality of the oxide film. Different materials of aluminum alloy, bare aluminum and pu
35、re parts or different sizes of aluminum and aluminum alloy parts, generally should not be treated with the tank oxidation.For aluminum alloy parts with overlapping, spot welding or riveting, aluminum alloy parts which are easy to form air bag in the course of anodic oxidation are not allowed to be u
36、sed in sulfuric acid anodizing process.(2) installation of fixture materials must ensure good conductivity, general use of aluminum alloy bar, plate to ensure that there is a certain degree of elasticity and strength. The retractor should be made of copper or copper alloy material. Used special or g
37、eneral purpose fixtures such as anodized, which must be completely removed from the surface oxide film to ensure good contact. The fixture must ensure sufficient conductive contact area and minimize the fixture mark. If the contact surface is too small, it will cause burns, corrosion, anodizing part
38、s.(3) the temperature of sulfuric acid anodizing solution must be strictly controlled, and the optimum temperature range is 1525. During the process of sulfuric acid anodizing, compressed air should be used for mixing and refrigeration equipment shall be provided. In the absence of refrigeration dev
39、ice under the condition of adding 1.5% 2% propylene acid or oxalic acid, lactic acid and carboxylic acid in sulfuric acid electrolyte, anodic oxidation solution can make the temperature range more than 35 DEG C and to avoid or reduce the loose powder or film. Some process test and production practic
40、e has proved that adding carboxylic acid or glycerin can effectively reduce the adverse effects of reaction heat effect in sulfuric acid anodizing electrolyte, anodic oxidation can improve the temperature of the electrolyte allows limit does not decrease in film thickness and hardness of the conditi
41、ons, under the premise of guaranteeing quality, improve production efficiency. In addition, under the condition of constant temperature control, we should pay attention to the effective control of the anode current density, in order to ensure the quality of the oxide film.(4) the water used in the a
42、nodizing of sulfuric acid and the harmful impurities in the electrolyte must be strictly controlled. It is not suitable to use tap water to prepare sulfuric acid anodizing solution, especially muddy water with high content of Ca2+, Mg2+, SiO32- and Cl-. Under normal circumstances, when the concentra
43、tion of Cl- in water reaches 25mg/L, it will have a harmful effect on Anodizing of aluminum alloy. Cl- (including other halogens) can destroy the oxide film formation, and even did not form an oxide film. Sulfuric acid anodizing should use soft water, deionized water or distilled water, electrolyte
44、Ccl- less than 15mg/L, the total mineral is less than or equal to 50mg/L.During the anodic oxidation process, oil, foam and suspended impurities will be produced in sulfuric acid solution, which should be removed regularly. Other harmful impurities, such as Cu2+, Fe3+, Al3+ and so on, are common in
45、sulfuric acid anodizing solution. If the impurity content exceeds the allowable content, it will have harmful effects, and the sulfuric acid anodizing solution can be effectively guaranteed by replacing sulfuric acid solution partially or completely.Anodized anodizing of aluminum alloy is a widely used and mature anti-corrosion treatment process. As long as the process conditions are strictly observed and operated carefully, the quality of anodizing film is absolutely guaranteed