Effect of Alloy elements on Properties：
The aluminum alloy of 6063 is a kind of heat treatable strengthening alloy with medium strength in AL-Mg-Si system. Mg and Si are the main alloy elements. The main work of optimizing chemical composition is to determine the percentage content (mass fraction, the same below) of Mg and Si.
1. The role and influence of Mg : The higher the content of Mg2Si, Mg in the strengthening phase of Mg and Si, the more Mg2Si, the greater the strengthening effect of heat treatment, the higher the tensile strength of the profile. However, the deformation resistance increases, while the plasticity of the alloy decreases and the workability and resistance becomes worse.
2. The role and influence of Si : The amount of Si should enable all Mg in the alloy to exist in the form of Mg2Si phase in order to ensure that the role of Mg can be used fully. With the increase of Si, the grain size of the alloy becomes finer, the metal flowability, the heat treatment strengthening effect improve, the tensile strength would increases. In the meantime, the casting property becomes better, the plasticity decreases, while the corrosion resistance becomes worse.
The corrosion behavior of the aluminum alloy of 6063 which caused by silicon can be completely prevented and controlled. As long as effectively controlled the incoming raw materials and alloy composition to ensure that the ratio of magnesium to silicon is in the range of 1.3 to 1.7. In addition, the parameters of each processare strictly controlled to avoid segregation and ionization of silicon, and that make silicon and magnesium form beneficial Mg2Si strengthening phase as far as possible.
If the phenomenon of silicon corrosion point is found, it should pay special attention to the use of weak alkaline bath solution as far as possible in the process of degreasing and deoiling. If the conditions are not adequate, the time of soaking in acidic deoiling solution should be shortened as much as possible. ( It is no problem for qualified aluminum alloy profiles to put 20~30min in acidic degreasing solution, but the problematic profiles only 1~3min can be placed on). And after that, the pH value of the washing water should higher than before. (pH>4, control the content of Cl-) The corrosion time should be prolonged as far as possible in the process of alkali corrosion. Nitric acid should be used to produce light solution when neutralizing light. And electrooxidation should be turned on as soon as possible during the process of anodizing of sulfuric acid. So that, the dark gray corrosion point caused by silicon will be hidden, which can meet the requirements of use.