冷却速率对Zn-3.5Mg合金凝固组织的影响

Effects of Cooling Rate on Solidification Structure of Zn-3.5Mg Alloy

通过SEM、EDS、XRD,研究了用于热浸镀锌的Zn-3.5Mg合金在3种不同冷却条件(炉冷、空冷和水冷)下的凝固组织。结果表明,随着冷却速率的增加,先共晶时析出的金属间化合物相在随后的的包晶反应(γ-MgZn2+L→β-Mg2Zn11)中逐渐被抑制,炉冷时金属间化合物相为β-Mg2Zn11,空冷时为β-Mg2Zn11包裹着γ-MgZn2,水冷时为γ-MgZn2相;平衡共晶组织α-Zn+β-Mg2Zn11(Eαβ)的数量减少,而非平衡共晶组织α-Zn+γ-MgZn2(Eαγ)的数量增多;先共晶金属间化合物粒子和共晶组织均被细化,先共晶粒子的宽度d和共晶间距λ与冷却速率c的关系近似满足d∝c-1/2、λ∝c-1/2。

Solidification structure of Zn-3.5Mg alloy for hot-dipping galvanizing under different cooling conditions, such as furnace cooling, air cooling and water cooling, were observed by SEM (scanning electron microscope), EDS(energy dispersive spectrum) and XRD (X-ray diffraction). The results indicate that with the increase of cooling rate, (1) the peritectic reaction of γ-MgZn2 +L→β-Mg2Zn11 of intermetallic compound particles precipitated from the primary eutectic reaction is restrained gradually, resulting in the creation of β-Mg2Zn11 intermetalic compound phase in furnace cooling, γ-MgZn2 phase enwrapped by β-Mg2Zn11 phase in air cooling and γ-MgZn2 phase in water cooling. (2) amount of the equilibrium eutectic phase α-Zn +β-Mg2Zn11 is reduced, while amount of the non-equilibrium eutectic Zn+γ-MgZn2 phase is increased. (3) both the primary eutectic intermetallic compound particles and eutectic structure can be refined. Meanwhile, the width of the particles and eutectic spacing have a certain relation with cooling rate.