目的 研究热镀铝锌硅镀层显微组织、弯曲对镀层裂纹形成的影响,探讨镀层裂纹的形成机制,为拓展热镀铝锌硅镀层钢板在冲压成形领域的应用提供依据。方法 采用高温热台装置,制备600 ℃保温时间为0.5、1、1.5 min的热镀铝锌硅镀层合金化试样,研究了镀层、镀层/钢基体界面合金层的显微组织,测试了τ5相的显微硬度,采用钢板弯曲试验,研究了热镀铝锌硅镀层裂纹的形成规律。结果 热镀铝锌硅镀层的凝固层显微组织为α(Al)富铝相、α(Al)+β(Zn)富锌相、少量针状Si析出相、微量Al-V-Ti相,基体界面主要是τ5相(Al8Fe2Si)、Fe3Al金属间化合物合金层;随着保温时间增加,金属间化合物合金层厚度增加,形成多层梯度分布结构,自内向外依次为Fe3Al、FeAl3、τ5相;Al-Zn-Si合金、Al-V-Ti相、τ5相的显微硬度分别为85、390、733HV0.2;厚度为1、2 mm的DC51D+AZ热镀铝锌硅镀层钢板界面合金层厚度为1~2 μm,1.5a180°、0a180°弯曲时,钢板外表面镀层裂纹最大宽度分别约为55、77 μm。结论 热镀铝锌硅镀层界面合金层中的高硬度τ5相是镀层形成裂纹的关键因素;600 ℃时τ5相的生长动力学表达式为y=8.06x0.2-8.92,符合抛物线关系;随着弯曲角度增加,折弯钢板间隙逐渐减小,弯曲的应变量增加,金属间化合物合金层、镀层弯曲外表面的裂纹宽度增加;镀层弯曲变形时,界面合金层的τ5相柱状晶首先开裂,形成有高密度纹理特征的微裂纹,有利于吸附胶状腐蚀产物,仍具有较好的耐蚀性,通过镀层的显微组织调控,能够兼顾实现热镀铝锌硅镀层钢板的成形性与耐蚀性。
Abstract
The work aims to investigate the effects of microstructure and bending deformation of hot-dip aluminum-zinc- silicon coated steel plate on coating cracks, and then explore the formation mechanism of coating cracks, so as to provide a basis for expanding the application of hot-dip aluminum-zinc-silicon coated steel plate in the field of stamping and forming. The hot-dip Al-Zn-Si coating alloyed samples with holding time of 0.5, 1 and 1.5 min at 600 ℃ were prepared by high-temperature hot stage experiment device, the microstructure of the coating and interface and the microhardness of τ5 phase were studied. Furthermore, bending tests were carried out to explore the formation of Al-Zn-Si coating cracks. The hot-dip Al-Zn-Si coating consisted of intermetallic alloy layer and solidification layer from inside to outside, the solidification layer consisted of α(Al)-rich phases, α(Al)+β(Zn) zinc-rich phases, a small amount of acicular Si precipitated phases and micro phases of Al-V-Ti, the intermetallic alloy layer mainly consisted of τ5 phases (Al8Fe2Si) and diffusion layer of Fe3Al. The thickness of the intermetallic alloy layer increased with the increasing holding time at 600 ℃, the multi-layer gradient distribution structure formed and the growth kinetic expression of of τ5 phases at 600 ℃ was y=8.06x0.2-8.92, which conformed to the parabolic relationship. The microhardness of Al-Zn-Si alloy, Al-V-Ti phases and τ5 phases were 85, 390 and 733HV0.2 respectively. The high hardness τ5 phase in the interface alloy layer of the hot-dip aluminum-zinc-silicon coating was the key factor for the formation of cracks in the coating. The thickness of the interface alloy layer of the hot-dip aluminum-zinc-silicon coated steel plate with the thickness of 1 and 2 mm was about 1-1.5 and 1.5-2 μm respectively. For bending at 1.5a180°, the maximum crack gap width of the coating on the outer surface of the DC51D+AZ coated steel plate with a thickness of 2 mm was about 55 μm. For bending at 0a180°, the crack gap width of the interface alloy layer was about 1-3 μm, and the maximum crack gap width of the outer surface coating was respectively about 75 and 77 μm, respectively. With the increase of the bending angle, the gap of curved steel plate decreased, the bending strain increased, and the width of cracks on the curved outer surface of intermetallic compound alloy layer and coating increased gradually. When the coating was bent and deformed, cracking in the columnar crystals of τ5 phases occurred firstly at interfacial alloy layer, forming micro-cracks with high density texture characteristics, which was conducive to the adsorption of colloidal corrosion products with better corrosion resistance. Through the microstructure control of the coating, the formability and corrosion resistance of hot-dip aluminum-zinc-silicon coated steel plate would be realized together.
关键词
热镀铝锌硅镀层 /
显微组织 /
τ5相 /
硬度 /
弯曲 /
裂纹
Key words
hot-dip Al-Zn-Si coating /
microstructure /
τ5 phase /
hardness /
bending /
crack
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