Hot dipped galvalume steel sheet is in aluminum zinc alloy structure. And hot dipped galvalume steel sheet is composed of 55% aluminum, 43.4% zinc and 1.6% silicon to solidify at 600 ℃ high temperature. The entire structure is a kind of alloy that use aluminum- iron- silicon- zinc to form a dense quaternary crystals. The main process features are as follows:
1. The temperature when put the strip into pot
The temperature when put strip into pot should be higher for about 50 ℃ than the temperature of zinc liquid. So that the main pot can not be heated. Relying on the temperature of strip into pot to maintain the thermal balance of zinc pot. However, because the ceramic zinc pot will cause damage to the melt channel without heat. So it always adopts low power to maintain a slow flow of zinc solution in the melt channel.
However, the aluminum-zinc plating pot body must adopt strong magnetic field mixing to maintain normal production. And the guarantee of the strong magnetic field have to increase the power supply. Therefore, the temperature when put the strip into pot of zinc-aluminum coating strip is lower for about 50 ℃ than the bath temperature, the strip absorb a lot of heat in the pot and provide a chance for the high-power heating of pot. According to experience, the temperature when put the strip into pot is generally controlled at 570-580 ℃.
2. The temperature of plating solution
From the equilibrium diagram of aluminum and zinc states, the lowest temperature when the aluminum-zinc alloy enter into the liquid region from the solid phase is 590 ℃. Known from the test that it all can be plated qualified aluminum zinc plated plate from 590 ℃ to 650 ℃. However, taken together from energy saving, zinc saving, operating environment, higher temperatures for production operations should not be taken. According to production experience of NAM KIM STEEL, adopting 600 ℃ as the target operating temperature is more appropriate.
3. The chemical component of plating solution
① The control range of chemical component in plating solution is: Al, 55%±1.5%; Zn, 43.5%±1.5%; Si, 1.5%±0.10%; Fe, less than 0.45%
About the problem of adding rare earth elements. When adding 0.1% rare earth elements into the cladding material of hot-dip 5% Al-Zn, the purpose is to refine the grain. Also add 0.1% of the mixed rare earth elements in 55% Al-Zn-Si coating alloy, it may have effect on refining the grain and forming the dense cladding material.
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