复合改性处理对AZ91镁合金表面结构和耐蚀性能的影响

Effect of surface modification on microstructure and corrosion resistance of AZ91 magnesium alloy by duplex ion implantation

为改善AZ91镁合金的耐蚀性能,对其表面进行了固溶时效和氮铝(N+Al)双离子注入复合改性处理。通过X射线衍射(XRD)、俄歇电子能谱(AES)、电化学综合测试系统、显微硬度计分析比较了处理前后试样的表面结构、元素浓度-深度分布、抗腐蚀性能和显微硬度。XRD结果表明,双离子共注后AZ91镁合金表面改性层由Mg、Al12Mg17、MgAl2O4、AlN等物相组成,且Mg和Al12Mg17衍射峰位和强度发生了明显改变。AES分析发现,表面存在约30 nm由Mg、Al、O等元素组成的改性层,注入层深度达到130 nm。双离子共注后试样的显微硬度较基体和固溶时效时分别提高了27.1%和10.4%。在3.5%饱和NaCl溶液中,双离子共注入试样的极化电阻分别为基体和固溶时效试样的21.7倍和9.1倍,腐蚀电流密度降为基体的1/10。相同腐蚀条件下的双离子共注入试样表面只产生了少量腐蚀斑,而基体和固溶时效试样表面却出现了大量的腐蚀坑。

In order to improve corrosion resistance of AZ91 magnesium alloy,solid solution and aging treatment and N/Al duplex ion implantation was conducted on the magnesium alloy surface.Microstructure,element distribution,corrosion resistance and hardness of the surface-modified alloy were analyzed by means of XRD,AES,electrochemical testing and micro-hardness measurement.XRD results show that the surface modification layer consists of Mg,Al12Mg17,MgAl2O4 and AlN phase,the diffraction peak position and intensity of Mg and Al12Mg17 shift obviously.AES analysis indicates that the modification layer of Mg,Al and O compounds with thickness of 30 nm exists in the surface.Compared with the untreated and heat treatment samples,micro-hardness of the duplex ion implantation sample increases by 27.1% and 10.4%,and the polarization resistance increases by 21.7 and 9.1 times.The corrosion current intensity of the modified alloy decreases by one order of magnitude in 3.5% NaCl saturated solution compared with that of the AZ91 alloy without modification.Duplex ion implantation sample produces less corrosion pits,but untreated sample and solid solution at and aged sample generates a large amount of corrosion pit,under the identical corrosion conditions.