The performance of Galvanized plate in high-temperature environments is constrained by both the phase transformation of the zinc coating and the change in the thermal strength of the substrate. Experimental data show that when the temperature exceeds 200℃, the common hot-dip galvanized layer begins to undergo liquid metal embrittlement (LME), resulting in a decrease of approximately 12% in the tensile strength of the substrate (tested in accordance with ISO 6892-2 standard). A typical case, such as the monitoring of the Saudi photovoltaic power station project in 2022, shows that the surface temperature of the galvanized steel support installed in the desert environment can reach 120℃. At this time, the oxidation rate of the zinc layer increases to three times that of the normal temperature environment, and the average annual corrosion amount reaches 15μm/ year, but the structural integrity is still maintained. The UL certification in the United States requires that galvanized parts for construction be used at temperatures below 149℃. If the temperature exceeds this limit, additional protective treatment is necessary.
When exposed to temperatures above 300℃, the thickening rate of the zinc-iron diffusion layer significantly accelerates, forming a brittle δ1 phase (FeZn10). Research from the Materials Laboratory of Drexel University indicates that after 24 hours of constant temperature exposure at 400 ° C, the G90 standard zinc coating (275g/m²) experiences a 30% thickness loss, while the yield strength of the base steel decreases by 9.5%. This explains the disaster case in the 2019 California wildfires where galvanized steel guardrails collapsed structurally within 16 minutes in a 420℃ fire environment, far exceeding the 25-minute failure time of ordinary steel.
The thermal cycling environment causes even more damage to galvanized steel sheets. The durability test of the automotive exhaust system shows that under the alternating impact of 550℃ high temperature (20 minutes) and 80℃ cold water (5 minutes), the galvanized layer without alloying treatment cracked after only 50 cycles, with a crack density of 8 per cm². However, the product with zinc-iron alloying process (GA) can withstand 300 cycles, and the surface damage rate is reduced by 60%. Data from BYD’s electric vehicle factory shows that its heat-resistant galvanized exhaust pipe assembly still retains an effective zinc layer of 18μm after 300,000 kilometers of driving, with the corrosion rate controlled at 0.15μm per thousand kilometers.
Technological innovation has significantly improved high-temperature performance. The zinc-aluminum-magnesium coating (ZM) developed by Nippon Steel of Japan can maintain structural stability for 2.3 times longer at 650℃, and the oxidation weight gain rate is only 0.8mg/cm²·h (3.5mg/cm²·h for ordinary galvanized coatings). The engine hood of the construction machinery adopted by Sany Heavy Industry with this technology has its service life extended from 5 years of conventional galvanized sheets to 9 years under continuous 250℃ working conditions, and the maintenance cost has decreased by 40%. Cutting-edge solutions such as laser in-situ alloying technology can increase the strength retention rate of galvanized steel sheets to 87% at 400℃, which is much higher than the 65% of traditional products. The weathering galvanized steel sheet (BNH400) mass-produced by Baosteel Group in 2023 has been successfully applied to transmission towers in the high-temperature and high-humidity regions of Southeast Asia. It is expected to have a service life of 30 years in an average annual temperature environment of 60℃, with the zinc coating consumption rate controlled at 1.2μm per year.