The 6063 aluminum alloys are usually used to produce the smart phone shells because of good mechanical properties and high surface qulitiy. The billets were produced in the direct-chill casting process and extruded into sheets. After machining and anodic oxidation coloring, the phone shell of aluminum alloy was produced. However, many defects, especially closely arranged long strip and randomly appeared strips were usually observed on the finished surface of the mobile phone shells, which resulted in a huge material waste. This paper characterized the causes of surface defects and considered that the particles of the inclusions remained in the melt is the main reasons that resulted in the strips defects formation, not only distributed on the surface, but also inside the phone shells. MgO, A12O3, spinel (MgA12O4) and Ti containing particles are the main inclusions that present inside the melt and have a strong deleterious effect on the surface smoothness.