The CNC anodized casing usually has a high yield and a good appearance, but the cost is high, the amount of CNC is large, and the processing cycle is long. For high quality situations, such as the Apple series, this is typically a high cost.
Take the smartphone case as an example. When using the CNC, it takes more than 30 minutes to complete the cut. Along with the completion of the work, it is estimated that it takes an hour. The die casting process takes only 20 to 30 seconds to complete and can be finished in 10 to 20 minutes. The die-cast housing is molded from a mold, so the processing time is short and the cost is relatively low. However, die-cast aluminum is difficult to anodize.
Why is it difficult to make an anode for die-cast aluminum?
Aluminum anodizing process basics
Anodizing is an electrochemical method in which an alloy portion is used as an anode, stainless steel, chromium or a conductive electrolyte itself is used as a cathode, and the anode is oxidized under a certain voltage and current conditions to obtain an anodized film on the surface of the workpiece. The process requires anodization with sulfuric acid during the anodization process , anodized aluminum electrical conductivity.
Limiting aluminum alloy by anodizing sulfuric acid
The presence of alloying elements reduces the quality of the oxide film. Under the same conditions, the oxide film obtained on pure aluminum is thicker, has higher hardness, better corrosion resistance and better uniformity. For the aluminum alloy material, in order to obtain a good oxidation effect, it is necessary to ensure the aluminum content, and it is usually preferably not less than 95%.
2. In the alloy, copper will turn the oxide film red, destroy the electrolyte quality and increase the oxidation defect; silicon will make the oxide film gray, especially when the content exceeds 4.5%, the effect is more obvious; black will appear after anodization point.
Die-cast aluminum alloy
Cast aluminum alloys and die castings usually contain high silicon content and the anodized film is black. It is impossible to obtain a colorless transparent oxide film. As the silicon content increases, the anodized film ranges in color from light gray to dark gray to dark gray. Therefore, cast aluminum alloys are not suitable for anodization.
Commonly used die-cast aluminum alloys can be divided into three categories:
One is an aluminum-silicon alloy, mainly including YL102 (ADC1, A413.0, etc.) and YL104 (ADC3, A360);
The second type is aluminum silicon copper alloy, mainly including YL112 (A380, ADC10), YL113 (A383, ADC12), YL117 (B390, ADC14);
The third type is aluminum-magnesium alloy, which mainly contains 302 (5180, ADC5, ADC6).
Aluminum silicon alloy, aluminum silicon copper alloy
For aluminum-silicon alloys, aluminum-silicon-copper alloys, as the name implies, silicon and copper are the main components other than aluminum; usually, the silicon content is between 6-12%, which mainly serves to improve the fluidity of the alloy liquid. The copper content is second only to, mainly to enhance the strength and tensile strength; the iron content is usually between 0.7% and 1.2%, wherein the release effect is better; it can be seen from the composition that it is impossible to oxidize and coat the alloy. Even with desiliconization, it is difficult to achieve the desired effect. In the case of an aluminum-silicon alloy or an aluminum alloy having a high copper content, it is difficult to form an oxide film, and the resulting film is dark, gray, and has poor gloss.
Since the aluminum-magnesium alloy oxide film is easy to mold, the film quality is also good, and it can be oxidized and colored, which is an important feature that is different from other alloys; however, there are some disadvantages.
1. The anodized film has duality, large pores and uneven distribution, and it is difficult to obtain better anticorrosive effect;
2. Magnesium has a tendency to produce brittleness, reduce elongation, and increase thermal cracking, such as ADC5, ADC6, etc. In production, due to its wide solidification range, large shrinkage tendency, frequent shrinkage and cracking, casting performance is very good, therefore, The scope of its use is very limited, and the structure with a slightly complicated structure is not suitable for production at all;
3, the aluminum-magnesium alloy commonly used in the market, due to its complex composition, low purity of aluminum, anodizing of sulfuric acid, it is difficult to produce a transparent protective film, mostly milky white, the color state is also poor, it is difficult to achieve the expected effect according to the normal process. .
In summary, it can be seen that the commonly used die-casting aluminum alloy is not suitable for sulfuric acid anodization; however, not all die-cast aluminum alloys can not achieve the purpose of oxidation coloration, such as aluminum-manganese alloy.
Die-cast aluminum anodizing solution
Die-casting parts can complete the structure, angular line and oxidation quality of forging parts, car parts/CNC parts, and the quality of the die-casting parts is very important. A small change, detailed process control determines the quality of the anode. . Manufacturers engaged in the oxidation of die-casting parts must scientifically control the flow path technology, die-casting process and post-processing method of the mold. With this series of strict control processes, the quality of oxidation can be ensured smoothly.
Mold runner, gate design, mold temperature control; due to the large aluminum content, poor fluidity and high working temperature, the flow path and gate of the mold are designed with short range design as the criterion; The mold temperature machine is used to ensure the equilibrium temperature of the mold, and the local overcooling is overcome, and the flow marks are excessive;
The use of raw materials to avoid pollution factors; the selection of low-molecular materials; in the production and use, to eliminate the pollution of silicon, copper, iron and zinc, that is, high-quality graphite crucible must be used alone, and can not be mixed with other raw materials.
Die casting process control, reduce watermark and black watermark; use professional release agent in die casting production, scientific spraying, reduce residual water in the cavity, avoid pressure casting water grain; control die casting pressure and speed, reduce local filling overpressure, Easy to stick mold;
Pre-blank processing; after machining, according to the needs of the product, manual polishing or grinding to remove burrs and oxide layers;
The choice of anode surface treatment plant; because the bottom layer of the die casting contains different degrees of shrinkage holes and stains; therefore, the anode pretreatment must be based on the conventional aluminum alloy process, and the method of adjusting the surface oxide layer of the casting can be performed before the anode process can be performed. That is to say, the conventional oxidation process can not meet the oxidation process of die-casting parts. Before mass production, it should be tested and audited to verify the suitable professional manufacturers.