Investigations on the Corrosion Properties of Uncoated, Al - Si Coated and Hot - Dip Pure Zinc Coated Hot - Stamped Steel Plates

Abstract

In the last years, hot - stamped coating steel plates have been used to automobile lightweight parts widely to meet the increasingly stringent regulatory requirements for fuel consumption and greenhouse gas emissions while promoting passenger safety. Using metallographic microscope, scanning electron microscope (SEM) and salt spray test chamber, the coating morphology and corrosion performance of uncoated, hot - dip pure zinc coated and Al - Si coated hot - stamped steel plates were compared and investigated. Results showed that the metallographic structure of the three hot - stamped materials was mainly martensite with a small amount of retained austenite; the coatings of Al - Si coated and zinc coated hot - stamped steel plates were complete, and no cracks penetrating the base material were found; the decarburized layer depth of uncoated hot - stamped steel plate was about 10 μm, the Al - Si coating consisted of α - Fe, Fe2Al5, FeAl and Fe2Al5 layers, and the zinc coating was mainly composed of α - Fe phase; the time spans for occurring 5% red rust in neutral salt spray (NSS) environment for uncoated, Al - Si coated and zinc coated hot - stamped steel plates were 6, 76, 96 h, respectively, and the corrosion depth was 257, 134, 66 μm, respectively. Besides, in NSS environment, the corrosion width for uncoated, Al - Si coated and zinc coated hot - stamped steel plates with electrophoretic treatment was 75.6, 42.3, 143.8 μm and the corrosion depth was 32.2, 7.0, 2.5 μm, respectively. The corrosion resistance was zinc coated electrophoretic plate > Al - Si coated > uncoated plate in order.

Keywords

• hot - stamped steel|al - si coating|pure zinc coating|corrosion properties