[China Aluminum Network] As with the Zn plating, the Al-Zn-Si plating layer is composed of a surface coating and an intermediate alloy layer. The difference is that the alloy layer grows very quickly, and the composition of the surface layer is solidified. Process and organizational structure are also very different.
The solidification process of A1-Zn-Si melt is fundamentally different from galvanization. The solidification point of pure zinc is unchanged, and the composition is also constant. Basically, nucleation grows at the same temperature, until the final solidification, the composition of each part of the zinc flower is basically the same. The solidification of the Al-Zn-Si melt takes place in a temperature range, and the high-aluminum structure is the first to crystallize, and the high-Zn structure is more crystalline than the final crystal.
In the equilibrium state, when the melt of the 550% Al-43.5% Zn-1.6% Si composition crystallizes, the main product is a solid solution of zinc in aluminum, which is a Zn-containing aluminum structure that occurs when the temperature is lowered again. The reaction is analyzed to produce a very fine Zn-rich phase. Such a structure is similar to that of a pure aluminum coating, so it does not achieve the comprehensive properties we need. Therefore, in practice, rapid forced cooling must be used to obtain a large degree of undercooling of the coating melt, forming a pseudo-eutectic structure, that is, most of the aluminum-rich zinc dissolved in the solid solution of aluminum and a small part of the rich Zinc aluminum dissolves in solid solutions in zinc.
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