1. Inadequate cleaning: Before polishing, the surface of die-cast aluminum parts must be thoroughly cleaned and any grease or dirt removed. If the cleaning is not thorough or the cleaning agent remains, it will affect the adhesion of the subsequent coating and coating, resulting in unqualified salt spray test.

2. Uneven grinding: If the grinding process is not uniform enough, some areas may be rougher than others, which will lead to uneven adhesion between coatings and problems in salt spray testing.

3. Coating quality: The coating quality will also affect the salt spray test results. If the coating thickness is insufficient, the adhesion is not strong or there are bubbles and other defects, the salt spray test will be unqualified.