Hot-dipped Alu-zinc steel in 55% aluminum appears no rust after 20 years application. Steel sheet only with zinc coating or 4% aluminum galvanization appears rust after about 10 years. Steel sheet with 7% aluminum galvanization appears rust after 9 years.Measured result of weight loss owing to corrosion shows the fact that steel sheet with 55% aluminum galvanized can be free from rust for minimum 50 years.Its base material is aluminum galvanized steel with 55% aluminum. Duration free from rust can last at least 50 years.http://www.steelcoilchina.com/pid11369884/Hot+dipped+Al-Zn+alloyed+coated+steel+coils.htm