Aluminum Coating Type 1 Aluminum Silicon Alloy

Type 1 aluminum coating is a thinner, aluminum-silicon alloy coating intended primarily for applications requiring formability and resistance to high temperatures, such as automobile exhaust components. Type 1 aluminum coatings are also applied to improve appearance. For most uses, the usual thickness of a Type 1 coating (Class 40) is about 20 to 25 pm (0.8 to 1 mil). When maximum formability is a critical requirement, a thinner 12 pm (Class 25) coating is specified.

Silicon is present in a Type 1 coating in the range of 5 to 11% in order to prevent formation of a thick iron-aluminum intermetallic layer, which would impair coating adherence and formability. Instead, a thinner iron-aluminum-silicon alloy layer is formed (Fig. 12).

Fig. 12 Type 1 aluminum coating microstructure. Scanning electron microscope cross section

Aluminum has a more detrimental effect than zinc on the spot weldability of steel sheet. Accordingly, aluminum Type 1 and Zn-55Al alloy coatings show the lowest tip lives among the hot-dip-coated products listed in Table 6.

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