30-04-2014 дата публикации
Номер: NZ597077A
NZ 597077 The disclosure relates to a method of forming a metal coated strip, such as a steel strip, which comprises: (a) passing the strip through a hot dip coating bath that contains Al, Zn, Si, and Mg and optionally other elements and forming a molten Al-Zn-Si-Mg alloy coating on the strip, (b) cooling the coated strip, preferably at a rate of at least 600ºC/sec, to solidify the molten Al-Zn-Si-Mg alloy on the strip and form a solidified coating having a microstructure that comprises alpha-Al phase dendrites, Zn-rich phases in interdendritic regions, and Mg2Si phase particles in interdendritic regions; and (c) heat treating the coated strip at a temperature of at least 300°C and for a time, preferably between 15 to 30 minutes, to form an Al-Zn phase solid solution from the as-cast microstructure of alpha-Al phase dendrites and the Zn-rich interdendritic phases and to facilitate globularisation of the Mg2Si phase particles that are dispersed in the coating; and (d) cooling the heat treated strip at a rate that minimises growth of Mg2Si phase particles and at least substantially retains the globular Mg2Si phase particles that form in the heat treatment step (c). Also disclosed is a strip, such as a steel strip, that has a coating of an Al-Zn-Si-Mg alloy on the strip that has a microstructure that comprises a solid solution of an Al-Zn phase and a dispersion of particles of Mg2Si phase in the coating, with the Mg2Si particles having: (a) a particle size of ≤ 2 microns, and (b) a globular shape.
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