Aluminum coating pretreatment technological process of a lot of, can according to the specific circumstances, such as workshop condition namely, space position and size, the workpiece material (manufacture, hot-rolled plate, galvanized sheet, aluminum alloy, glass fiber reinforced plastic, etc.), surface condition (corrosion, rust-proof oil, sundry), production batch, quality requirement of choice. Different manufacturers adopt different processes, such as the overall process and quality requirements of passenger cars, and the following two kinds of processes are generally:

1. Pre-production processing

2. Pre-product processing

    The process control elements are described as follows:     

    1. skim  

        （1）free alkalinity（FAL）

        （2）the temperature of the degreasing fluid 

        （3）processing time

        （4）mechanical effects

        （5）oil content of degreasing fluid       

    2. pickling       

        （1）free acidity（FA）

        （2） temperature and time

        （3）pollution aging     

    3. table           

        （1）impact of water quality 

        （2）use time  

    4. phosphating    

        （1）acid ratio (ratio of total acidity to free acidity)

        （2）temperature

        （3）sediment discharge

        （4）nitrite NO-2 (promoter concentration) 

        （5）so2-4 sulfate

        （6）ferrous ion Fe2+Fe2+

    5. Passivation (closed)

    6. Water washing