| Hot dip Al-Zn alloy coated steel sheet(55% Al-43.4% Zn-1.6% Si)is one kind of coated steel sheets with high corrosion resistance.It can provide excellent atmospheric corrosion resistance and heat endurance.Al-Zn alloy coated sheets have been widely used in construction,automobiles,home appliances and many other products.Al-Zn coated steel sheets with thickness bigger than 2.0mm are highly demanded in electric control cabinet products.These products require spangles with small size,usually 50~65spangles/100 mm.To satisfy the requirement of application manufacturing techniques,including hot-dipping temperature and cooling rate,need to be optimized.This study focused on the cooling process and the immersion process temperature in hot-dip,and studied how these two factors influence the spangle size and structure.In this study Al-Zn alloy coated samples with different cooling process and different combination of bath temperature and diving temperature were prepared by hot-dip simulation unit.Scanning electron microscope(SEM)and energy dispersive spectroscopy(EDS)were used to investigate the microstructure and element distribution of coating layers.Influences of cooling processes and hot dip temperature on spangle size and coating structure were analyzed.The main conclusions are as follows:(1)When cooling rate in 600?~520? interval increases from 5?/s to 25?/s,spangle size decreases from 3.1mm(32 spangles/100mm)to 1.4mm(71 spangles /100mm);When cooling rate in 520?~380? interval increases from 5?/s to 25?/s,spangle size decreases from 3.6mm(28 spangles/100mm)to 1.8mm(56 spangles /100mm);(2)600?~520? temperature interval is a key process during the whole cooling procedure.The effects of reducing spangle size and refining microstructure are enhanced when increasing cooling rate in this temperature interval.For thick steel sheet whose thickness is bigger than 2.0mm,higher cooling rate should be applied to reduce the spangle size.(3)When diving temperature increasing from 500? to 650?,spangle size decreases from 3.4mm(29 spangles/100mm)to1.9mm(53 spangles /100mm);when bath temperature increasing from 580? to 630?,spangle size decreases from 3.2mm(31 spangles/100mm)to1.9mm(53 spangles /100mm);... |
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