Preparation and deformation behaviour of multi-structural aluminium-coated steels

Multi-structural aluminium coatings were successfully fabricated on a steel substrate by a combination of magnetron sputtering and hot-dip aluminising to improve the formability of hot-dip aluminised steel. The deformation behaviour, formation mechanism and cracking failure of the multi-structural aluminium-coated steels (Al-HD/Al-MS-ST) were investigated through deep drawing. The coatings were composed of an outer Al layer and an inner Fe-Al intermetallic layer which consisted of a FeAl3 layer and a Fe2Al5 layer. Compared with hotdip aluminised steels, Al-HD/Al-MS-ST presented a sparsely arranged comb-tooth structure and a reduction in thickness of the intermetallic layer. Results indicated that I-cracks, II-cracks and secondary cracks can be generated in the intermetallic layer, and punch corner and flat surface area were susceptible to fracture during deep drawing. I-cracks propagated in the direction perpendicular to the coating/substrate interface, whereas II-cracks propagated parallel to the coating/substrate interface. Al-HD/Al-MS-ST exhibited excellent resistance to crack propagation and formability because of the comb-tooth structure and thin intermetallic layer.