Some specific methods for pre-treatment of aluminum and aluminum alloys are as follows:
① Organic solvent degreasing. Less severe oil stains can be soaked in solvents for a short period of time; Severe oil stains should be wiped with cotton yarn dipped in solvent or brushed with a bristle brush. Attention should be paid to safety during operation, and the remaining solvent should be properly stored after use.
② Air dry. Regardless of the cleaning method using any organic solvent, the drying process must not be omitted, otherwise it will lose its cleaning significance.
③ Binding. The material used for binding should be aluminum wire, copper wire and galvanized iron wire are prohibited, and iron wire with removed zinc layer can be used.
It is better to tie individual pieces of slightly larger ones, and try to tie them in the hole closest to the edge of the part as much as possible to reduce the impact on the surface of the workpiece.
Different types of workpieces should not be tied together in a string, as the oxidation treatment time of aluminum materials with different compositions (grades) varies.
Pay attention to the direction of the workpiece being tied when suspended, and avoid air pockets caused by the concave part facing downwards.
④ Alkaline washing
Sodium hydroxide steel 50-70g/L
Time: 0.5-2 minutes
Temperature 50-70 ℃
Alkali wash until the oil stains on the surface of the workpiece are completely removed.
⑤ Rinse with circulating water. It is best to rinse with hot water first after alkaline washing, which is beneficial for cleaning the alkaline substances on the surface of the workpiece. Workpieces with blind holes or narrow gaps should be rinsed thoroughly and any residual solution should be removed.
⑥ Nitric acid luminescence
Nitric acid 200-300mL/L
Time until the dark film recedes completely
Temperature room temperature
If dealing with miscellaneous aluminum and cast aluminum, hydrofluoric acid should be added on the basis of this formula to accelerate the removal of insoluble substances adhering to the surface of aluminum parts during alkaline washing.
