[Alcoa.com] Most of the previous mobile phone body materials are plastic, low cost, processing is difficult, but it is cheap, and the metal body are seen in a few flagship machines. However, with the development of the industry, up to the flagship machine to thousands of machines, the metal fuselage suddenly began to spread! The metal fuselage is widely used in aluminum alloys in the models of well-known brand manufacturers. The aluminum alloy in the design of the mobile phone is what design form appears, let us do some preliminary introduction:
The front class: the appearance of the middle box represents the model iphone6/6S, iPhone5S, HTCM8, vivoXshot, Lumia925, etc.
Material classification:
According to different alloy materials, aluminum alloys can be divided into 1 series to 9 series. The specific model names in each series are generally four digits, such as 6061, 7075. The body material of iPhone 6S is the 7 series aluminum alloy. . The 7-series aluminum alloy is mainly made of zinc, but also a small amount of magnesium and copper. The hardness of the aluminum alloy is closer to the hardness of the steel - but it is still a pit! The 6 series aluminum alloy mainly uses magnesium and silicon as the main alloying elements, and is currently the most widely used alloy.
Structural design method:
The overall CNC + nano-injection molding, the appearance of decorative pieces CNC + dispensing / paste adhesive / lock screws, the appearance of the surface CNC + internal aluminum alloy die-casting beer + nano-injection molding, forging + CNC + nano-injection molding, and so on.
Process treatment: Anodizing
Advantages: Compared to the low profile of stainless steel,
Aluminum alloys are easier to process with high-grade, beautiful, sparkling sensations. Secondly, the aluminum alloy material is very light, with a specific gravity of only one-third that of stainless steel, which means that the same volume of stainless steel mobile phone, the material is almost three times the weight of aluminum alloy. This is why the iPhone 5 is so lighter than the iPhone 4S. Third, scratch resistance, aluminum alloy material is not on the strength, but the surface hardness has reached the level of sapphire, so the use of aluminum alloy cell phone may have a close collision, but few scratches. Fourth, the aluminum alloy material is highly dyeable. It is because of the use of aluminum alloy, Iphone and other mobile phones can have what we call "local gold", "high-end gray" and other colors.
In addition, aluminum alloy materials and high temperature, no fingerprints, anti-static, environmental protection and other non-toxic characteristics.
Disadvantages: high cost
IPHONE6 drop paint door incident: some iPhone6S mobile phone use after a period of time "fall paint", the surface appears random flakes, the overall look "rust", like crawling with bugs, can not see the iPhone "Gao Yan The "value" feature, on the contrary, gives people a sense of horror.
Analysis of Main Reasons: The previous iPhone 6 had also used aluminum alloys with the brand name of 6 series as the mobile phone housing. The main alloying elements of this aluminum alloy are magnesium and silicon, and the alloy content is low, the anodic oxidation yield is high, and the oxide film has strong adhesion and adhesion. The protection of the aluminum alloy material is not corroded, so the above “rusting†condition does not occur. However, the major disadvantage of the 6 series aluminum alloy is its low strength. Therefore, the mobile phone is easily bent or bent. Apple has to use a higher-strength 7 series aerospace aluminum alloy.
The 7 series of aerospace aluminum alloys used in the iPhone 6S are higher in room temperature aluminum alloys, but are also more susceptible to corrosion. In addition to aluminum, this series of aluminum alloys also added zinc, magnesium and copper elements. It is the addition of these alloying elements that produces various strengthening phases to increase the strength greatly, which can reach 2-3 times that of ordinary low carbon steels, completely solving the problem of easy bending of the iPhone 6; however, it also leads to poor corrosion resistance of the series of alloys, and it is easy to Stress corrosion occurs.
In order to improve the corrosion resistance, the surface of the aluminum alloy housing of the mobile phone will be subjected to artificial anodizing to make the appearance more beautiful and increase the surface hardness. The quality and adhesion of the anodized film directly affect the appearance quality and corrosion resistance of the mobile phone. Due to the high alloy composition of the 7 series aluminum alloys, it is difficult for these alloying elements to avoid uneven distribution and segregation in the process of conventional casting of aluminum rods, also called macro segregation. Partial segregation will be partially improved during subsequent homogenization and extrusion of the aluminum row, but cannot be completely eliminated. The presence of segregation means that the distribution of the components of the material is not uniform, and the unevenness of the composition causes the quality and adhesion of the anodic oxidation film to be different, resulting in appearance defects such as color difference after oxidation, and unstable performance in use, partial position oxide film. Adhesion is not easy to fall off. Once the protection of the oxide film is lost, and the accelerated corrosion of hand sweat, moist air and hot weather, the 7 series of aluminum aluminum mobile phone cases used by the iPhone 6S will exhibit the above-mentioned phenomenon of “dropping paintâ€.
The segregation problem of the 7 series aluminum alloy material begins from the casting process and has been difficult to eradicate in the material, affecting the quality of anodizing, and eventually causing the iPhone 6S to “fall paint†seriously, making it difficult to look directly at. Therefore, to completely solve this problem, we must start from the source and try to produce high-quality, high-quality aluminum alloy raw materials without segregation.
Rapid cooling process for preparing high quality aluminum alloy raw materials:
(Lower left - rapid cooling 7075 aluminum alloy microstructure, the lower right cast 7075 aluminum alloy microstructure)
In the conventional casting process, due to the slower cooling rate of the solidified metal (generally <102°C/s), the alloying elements are liable to segregate and continue to grow, which seriously affects the uniformity of the material; while the rapid cooling process uses a very fast cooling rate (up to At 104-106°C/s), the liquid metal has a large degree of undercooling, which promotes nucleation; the metal completes the solidification in a very short time, so that the nucleation of the crystal is not enough to grow up; and it suppresses the branches commonly found in casting. The crystals and columnar crystals form approximately spherical equiaxed crystals, eliminating the anisotropy of conventional materials; due to the fine grain structure, the metal produces a fine grain strengthening effect, greatly improving the strength, hardness and plasticity of the alloy; rapid cooling The solidification of the alloy in the process is completed in the inert gas protection, without oxidation, inclusion, and the hard phase is fine and dispersed distribution. The uniform dense structure is favorable for the quality and uniformity of the anodized film, and improves the corrosion resistance.
Above is a comparison of the microstructure of Rapid Cool 7075 and Cast 7075. From the metallographic photographs, it can be seen that the 7075 grain of the casting is coarse, and the dendrite and segregation are serious; the rapidly cooling 7075 grains are spherical, no dendritic structure, and the grain is small. Table 1 shows the performance comparison of the 7 series aluminum alloy produced by the rapid cooling process and the conventional process. The figure below is a physical map of the rapid cooling 7 series aluminum alloy.
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