Some iPhone6S mobile phone may occur to flake paint when have been used for a time. Its surface presents random peeling spots, and the whole appearance looks rusty as if it was covered with insects, creepy and horrible. The iPhone’s value is totally decreased.

The main reason:

the previous iPhone6’s​ phone shell have also been produced with the 6 series aluminum profile whose alloy elements are magnesium and silicon and the content accounts for little, so that the anodic oxidation yield is high with a strong adhesion of oxide film to protect the aluminum profile from corrosion. Thus, the previous iPhone6 did not get rusty. But the biggest disadvantage of the 6 series aluminum is the low strength so that it is prone to bending. So the Apple Company had to choose the 7 series aluminum for aviation with a higher strength.

The 7 series of aviation aluminum used in IPhone6S has the highest strength in the aluminum at the normal temperature indoors, but also is easiest to corrosion. This series aluminum, addition to aluminum, is also composed with zinc, magnesium and copper. It is these alloy elements composed that the strength is enhanced 2-3 times the ordinary low carbon steel. The bending problem of iPhone6 ​​is solved. But the corrosion problem occurred instead.

In order to improve the corrosion resistance, the phone's aluminum shell surface will be artificial anodized, so as to improve the surface hardness and the appearance looks more beautiful as well. The quality and adhesion of the anodic oxide film directly affect the appearance quality and corrosion resistance of the phone. Due to the high quantity alloy composition of 7 series aluminum, these elements in the conventional casting process of aluminum rods is difficult to avoid uneven distribution, resulting in segregation, also known as macroscopic segregation. Partial segregation will be partially improved during subsequent homogenization and extrusion of aluminum, but can not be completely eliminated. The presence of segregation means that the distribution of material in various parts is not uniform. And the uneven composition will cause the different quality and adhesion of anodic oxide film then, resulting in defects after oxidation, such as uneven color appearance, the unstable using performance, part of oxide film peeling. Once losing protection from the oxide film, coupled with hand sweat, humid air and high temperature corrosion will be accelerated. Therefore, the paint flaking event happens on the iPhone6S.

The segregation problem of 7 series aluminum occurs along the process from casting to producing. It has been a headache problem, continually affecting theanodic oxidation. The complete solution to the problem should try to produce high end machining aluminum parts with high homogeneity and zero-segregation.


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