As the aluminum alloy Meter Case surface coating adhesion is poor, so the surface must be pretreated to form a surface conversion coating. This not only can enhance the coating adhesion, corrosion resistance but also greatly improved. Aluminum and aluminum alloy surface treatment is generally: Caustic,washing, ​​washing,go oxide chemical conversion , rinsing ,drain dry.

Aluminum and steel shell pre-treatment process has the following different pre-treatment.

1. Degreasing: The main purpose is to remove the caustic surface of aluminum buildup of oil. Commonly used by the Alkali lotion formula Na2CO3, Na3PO4, Na2SiO3 and additives, mainly with dip and spray can also be used electrolytic cleaning and ultrasonic cleaning.
2.  To remove the oxide film: the surface of naturally formed aluminum oxide film is non-uniform continuous film, the coating must be thoroughly cleaned before, die castings can be used for removal of nitric acid to the surface oxide film.
3. Chemical conversion: conversion process is intended to form a dense and uniform aluminum surface of continuous film. The role of this process is equivalent to the steel surface treatment process in the phosphating process, but its solution is different from the conversion coating of aluminum and aluminum alloy  Meter Case in chromic acid / hydrochloric acid, phosphoric acid / hydrochloric acid and hydrofluoric acid based conversion coating quality is usually to 215g/m2, after the formation of conversion coating must be washed with water, then dried with hot air, to enhance the film hardness.