退火孪晶对hcp结构二元镁锂合金腐蚀行为的影响

采用浸泡实验、电化学实验、腐蚀形貌观察以及扫描开尔文探针测试等实验方法对挤压态和退火态二元Mg-xLi（x=1，3，5，质量分数，%）合金的耐腐蚀性能进行研究。结果表明：挤压态Mg-Li合金经350 ℃/4 h退火处理后，可在基体中形成退火孪晶。在 0.1 mol/L NaCl溶液中，退火态合金的耐腐蚀性能明显劣于挤压态合金。通过扫描电子显微镜和激光共聚焦三维形貌分析，发现挤压态合金在腐蚀初期具有丝状腐蚀特征，并且随着腐蚀时间的延长形成了腐蚀坑；退火态合金表面发生快速腐蚀损伤，同时形成较大且深的腐蚀坑形貌。另外，退火态Mg-3Li合金的腐蚀等势线分布表明该合金退火孪晶区域优先发生了腐蚀溶解现象。因此，退火孪晶与母体晶粒之间可形成微电偶腐蚀效应，且退火孪晶区域充当阳极，母体晶粒作为阴极，从而降低了退火态Mg-Li合金的耐腐蚀性能。

Effect of Annealing Twins on Corrosion Resistance of hcp Binary Mg-Li Alloy

Corrosion resistance of as-extruded and as-annealed binary Mg-xLi (x=1, 3, 5, wt%) alloys was investigated via immersion tests, electrochemical tests, corrosion morphology observation, and scanning Kelvin probe tests. Results reveal that the annealing twins form in the as-extruded alloys after annealing at 350 °C for 4 h, and the corrosion resistance of the as-annealed alloys is obviously worse than that of as-extruded alloys in 0.1 mol/L NaCl solution. Typical filiform corrosion appears in as-extruded alloys at the initial corrosion stage, according to the analysis results of scanning electron microscope and laser confocal 3D morphology observation. Some corrosion pits are gradually formed with prolonging the corrosion duration. The rapid corrosion damage occurs on the as-annealed alloy surface, and meanwhile the relatively large and deep corrosion pits appear on the alloy surface. Besides, the distribution of isopotential line of corrosion indicates the occurrence of preferential corrosive degradation in the annealing twin areas. Thus, the micro-galvanic effect is formed between the annealing twins and parental grains with annealing twins as anode and parental grains as cathode, which decreases the corrosion resistance of as-annealed Mg-Li alloys.