Zn对挤压态Mg-3Sn-1Ca合金耐蚀性的影响

Effect of Zn on Corrosion Resistance of Extruded Mg-3Sn-1Ca Alloy

目的 提高挤压态Mg-3Sn-1Ca合金的耐腐蚀性能。方法 通过合金熔炼制备了Mg-3Sn-Ca(TX31)和Mg-3Sn-Ca-Zn(TXZ311)两种挤压态合金,利用XRD、金相、SEM、EDS、EBSD、析氢、电化学极化曲线和阻抗谱,分析了TX31和TXZ311两种合金的微观组织及耐腐蚀性能。结果 XRD和EDS结果表明,挤压态TX31和TXZ311两种合金中第二相均为CaMgSn相,TXZ311合金中由于Zn的添加,CaMgSn相增加且分布更加均匀。金相和EBSD结果表明,Zn的添加可以提高TX31合金的动态再结晶程度和{0002}基面织构强度,改善TX31合金中组织的不均匀性。从极化曲线上可得,腐蚀电位和腐蚀电流分别为-1.57V和6.95×10^(-5)A。添加Zn后,腐蚀电位升高(-1.49 V),腐蚀电流减小(1.02×10^(-5)A),表明合金耐蚀性提高。对比两种合金阻抗谱可发现,TXZ311合金具有比TX31合金更大的容抗弧,表明其表面的电荷转移电阻和表面膜的电阻最高,动态腐蚀过程中氧化产物膜具有较好的稳定性,有效阻碍了α-Mg基体的腐蚀。TX31合金析氢量和时间成正比,腐蚀速率为3.7mm/a。而TXZ311合金腐蚀速率仅为1.6mm/a,析氢量在腐蚀12 h后明显降低,表明合金表面形成了可以阻碍腐蚀进行的氧化膜。结论 Zn元素可以极大提高TX31合金的耐蚀性。这是由于添加Zn元素后,TXZ311合金腐蚀膜层间的黏附力增加,动态再结晶程度增高,晶粒组织更加均匀,{0001}基面织构强度增加。因此,TXZ311合金的耐蚀性远高于TX31合金。

To improve the corrosion resistance of extruded Mg-3Sn-1Ca alloy.Two as-cast alloys Mg-3Sn-1Ca and Mg-3Sn-1Ca-1Zn were prepared by alloy melting using industrial pure Mg(99.9wt.%),pure Sn(99.9wt.%),Mg-25%Ca intermediate alloy and pure Zn(99.9wt.%).The as-cast alloy was homogenized(400×24℃h).After homogenization,the ingot was processed into a 47 mm×100 mm casting blank with a diameter of 47 mm×100 mm by a lathe.The processed casting blank was preheated to 300 and put into a mold hea℃ted to 300.Reverse extrusion was carried out on a 300℃-ton vertical hydraulic press.After extrusion,the diameter of the bar is 12 mm.The microstructure and corrosion resistance of TX31 and TXZ311 alloys were analyzed by XRD,Metallography,SEM,EDS,EBSD,Hydrogen Evolution,Electrochemical Polarization Curve and Impedance Spectroscopy.The XRD and EDS results show that the second phase in the extruded TX31 and TXZ311 alloys is CaMgSn phase.Due to the addition of Zn,the CaMgSn phase increases and distributes more evenly in the TXZ311 alloy.The Metallographic and EBSD results show that Zn addition can improve the dynamic recrystallization degree of the TX31 alloy and the texture strength of{0001}base plane,and improve the microstructure heterogeneity of the TX31 alloy.From the polarization curve,the corrosion potential and corrosion current are‒1.57 V and 6.95×10^(‒5) A respectively.After Zn was added,the corrosion potential increased(‒1.49 V)and the corrosion current decreased(1.02×10^(‒5) A),indicating that the corrosion resistance of the alloy was improved.By comparing the impedance spectra of the two alloys,it can be found that the TXZ311 alloy has a larger capacitive arc resistance than TX31 alloy,indicating that the charge transfer resistance on the surface and the resistance of the surface film are the highest,and the oxidation product film has a good stability during the dynamic corrosion process,which effectively prevents the corrosion ofα-Mg matrix.The amount of hydrogen evolution of the TX31 alloy is proportional to time,and the corrosion rate is 3.7 mm/a.However,the corrosion rate of the TXZ311 alloy is only 1.6 mm/a,and the amount of hydrogen evolution decreases significantly after 12 h corrosion,indicating that an oxide film is formed on the surface of the alloy which can hinder the corrosion process.Zn element can greatly improve the corrosion resistance of the TX31 alloy.This is because after the addition of Zn element,the TXZ311 alloy dynamic recrystallization degree is higher,the structure is more uniform,so that the grain boundary and phase boundary are strengthened,inhibit the hydrogen evolution reaction of the cathode,and thus hinder the dissolution of the anode.Secondly,compared with the TX31 alloy with serious local corrosion,the corrosion film formed during the corrosion of the TXZ311 alloy has good adhesion,covers the alloy surface well,and effectively delays the corrosion of magnesium matrix.In addition,the texture also has a great influence on the corrosion resistance of the alloy.Studies have shown that the deformed magnesium alloy can increase the strength of the texture on the base plane and thus improve the corrosion resistance of the alloy,which is due to the higher atomic density and higher activation energy of the base plane.In this paper,the texture strength of TX31 alloy{0001}base plane is 7.29,and the addition of Zn element makes the texture strength of{0001}base plane reach 16.6,which makes a certain contribution to improve the corrosion resistance of the alloy.Therefore,the TXZ311 alloy corrosion resistance is much higher than the TX31 alloy.