What will happen if no primer is used in the spraying process of automobiles wheel hub?

As we all know, the current automobiles wheel hub spraying process is generally as follows: pretreatment → primer → drying → polishing → primer → paint → drying → transparent powder → drying. The purpose of spraying primer is to ensure the smoothness and stone strike resistance of the substrate surface, but what problems will occur if the primer free process is used in the spraying process of automobiles wheel hub?

In the traditional process, the primer and color paint are sprayed wet by wet. In the spraying process, the solvent volatilization is less. When the primer is not applied, the color paint and solvent are more likely to volatilize, so the paint film defects such as blooming are easy to occur at the corners. Considering the insufficient covering power of the paint itself, in order to achieve good leveling and appearance and reduce the defects of the paint film, it is more difficult to optimize the spraying angle and parameters than the primer spraying.