镁铝合金在模拟低温条件下大气腐蚀行为研究

Atmospheric Corrosion Behavior of Mg-alloys AZ31B and AZ91D in Simulated Low Temperature Environments

采用室内模拟方法研究了AZ31B和AZ91D镁合金在低温交变条件下的大气腐蚀行为。采用失重法得到两种镁合金的腐蚀速率与温度呈正相关,形貌分析表明在低温条件下两种镁合金均发生了明显的局部腐蚀。结合腐蚀速率和形貌观察,相同温度条件下AZ31B镁合金比AZ91D镁合金腐蚀严重,但AZ91D镁合金具有十分明显的点蚀特征,表现为AZ91D镁合金的平均点蚀密度和深度高于AZ31B镁合金,但其平均点蚀体积相对较小。红外光谱和能谱分析表明,在15~25℃温度循环时,Mg(OH)_(2)、MgO和碳酸盐是腐蚀产物的主要成分;而在低温循环(-5~-15℃和-5~-25℃)时,腐蚀产物中MgO的含量较高,EDS能谱检测到AZ91D镁合金点蚀严重的区域存在Al和Cl,Cl-对氧化膜的破坏作用对AZ91D镁合金的点蚀有重要影响。

The atmospheric corrosion behavior of Mg-alloys AZ31B and AZ91D at alternating low temperatures was investigated via laboratory simulation i.e.a high/low temperature dry-humid alternating test chamber.The corrosion rate of the two alloys was positively correlated with temperature as the results acquired by the mass loss measurement.The morphology analysis showed that the two alloys exhibited obvious localized corrosion in the low temperature environment.Combined with corrosion rate and morphology observation(SEM,CLSM),it was found that AZ31B Mg-alloy was more seriously corroded than AZ91D Mg-alloy at the same temperature,but AZ91D Mg-alloy showed obvious pitting characteristics.The average pitting density and depth of AZ91D Mg-alloy were larger than that of AZ31B Mg-alloy,but the corresponding average pitting volume was smaller.FTIR and EDS analysis showed that Mg(OH)_(2),MgO and carbonates were the main components of the corrosion products formed at 15-25oC,while the content of MgO in the corrosion products was higher at lower alternating temperatures(from-5oC to-15℃and-5oC to-25℃).EDS results suggested that Al and Cl were present in the area where AZ91D Mg-alloy pitting was serious.It was considered that the destruction of the oxide scale by Cl-had an important influence on the pitting corrosion of AZ91D Mg-alloy.