镁合金表面高转速搅拌摩擦加工区的微观组织和耐腐蚀性能

Microstructure and Corrosion Resistance of High Rotating Speed Friction Stir Processed Zone on Magnesium Alloy

目的采用高转速搅拌摩擦加工技术在AZ31B镁合金表面制备一层组织结构均匀化和致密化的加工层,改善镁合金表面的耐腐蚀性能。方法采用高转速搅拌摩擦加工技术对AZ31B镁合金表面进行单道次加工,并利用XRD、OM、EBSD、TEM和SEM分析不同转速下加工区的相组成、晶粒形貌、织构特征、二次相分布和表面腐蚀形貌,利用无纸记录仪和电化学工作站分别测试加工区的热循环曲线和表面耐腐蚀性能。结果经高转速搅拌摩擦加工之后,在AZ31B镁合金表面制备了宏观成形美观且微观组织结构明显细化、均匀化和致密化的加工区。加工区相组成与基材一致,均由α-Mg和β-Al_(12)Mg_(17)组成。加工区平均晶粒尺寸较基材明显细化,织构强度明显增大。随着转速的增大,加工区平均晶粒尺寸逐渐粗化,织构强度逐渐减弱,β-Al_(12)Mg_(17)相分布更加均匀弥散。加工区耐腐蚀性能较基材明显提升,自腐蚀电位由基材的–1.49 V增至–1.28 V,自腐蚀电流由基材的2.08×10^(–4)A减小至9.51×10^(–5)A。在转速为3000 r/min和加工速度为100 mm/min的工艺条件下,加工区展现出较佳的耐腐蚀性能。结论高转速搅拌摩擦加工可显著细化晶粒,均匀化和弥散化析出相分布,有效改善镁合金表面耐腐蚀性能。

The paper describes a work that aims to prepare a layer with homogenized and densified fine-grained structure on magnesium alloy by using high rotating friction stir processing for enhancing corrosion resistance.The phase compositions,grain morphologies,texture,precipitates distributions,and corrosion morphologies of the processed zone are processted in detail by using XRD,OM,EBSD,TEM,and SEM.In addition,the thermal cycling curves,potentiodynamic polarization curves and Nyquist spectra of the processed zone are ascertained by using the K-type thermocouples and a triple-electrode electrochemical workstation respectively.A sound processed zone is prepared by using the single-pass high rotating speed friction stir processing.The as-received AZ31B magnesium alloy and the processed zone are composed of equiaxed grainsα-Mg and needle-likeβ-Al_(12)Mg_(17) phases.The surface appearances of the processed zones are glossy and flat.Compared with the as-received AZ31B magnesium alloy,in addition to the obvious texture,the mean grain size in the processed zone is significantly refined,and the distributions of theβ-Al_(12)Mg_(17) phases were more uniform and dispersed.In addition to the weakening of the texture,the mean grain size and the number of theβ-Al_(12)Mg_(17) phases are gradually increased as the rotating speed increased due to the sufficient heat input.The peak temperature in the processed zone is increased with the increase of the rotating speed.High rotating friction stir processing obviously enhances the corrosion resistance of the AZ31 magnesium alloy due to the formation of fined grain size,and homogenized and diffused distribution ofβ-Al_(12)Mg_(17) phases.The processed zone produced at the rotating speed of 3000 r/min exhibits outstanding corrosion resistance.The corrosion potential of the processed zone increased from–1.49 V to–1.28 V,and the corrosion current reduced from 2.08×10^(–4) A to 9.51×10^(–5) A compared to those of the as-received AZ31 magnesium alloy.High rotating speed friction stir processing is proven to be the optimal path to enhance the corrosion resistance of the AZ31B magnesium alloy by effectively changing the microstructure characteristic.