Mn含量对Zn-Al-Mg合金组织和耐腐蚀性能的影响

Effect of Mn content on microstructure and corrosion resistance of the Zn-Al-Mg alloys

为了使热镀锌产品获得更好的耐腐蚀性能,通过感应熔炼制备了3种不同Mn含量的Zn-Al-Mg合金铸锭,分别为Zn1Al1Mg0.5Mn、Zn1Al1Mg1.2Mn、Zn1Al1Mg2.5Mn,并分析了其凝固组织和腐蚀行为。结果表明:通过相图计算预测了含Mn的Zn-Al-Mg合金中Al-Mn化合物类型为Al_(11)Mn_(4)、Al_(8)Mn_(5)、Al_(0.8)Mn;Zn1Al1Mg0.5Mn、Zn1Al1Mg1.2Mn合金的Al-Mn析出相分别为Al_(11)Mn_(4)、Al_(8)Mn_(5),随着Mn含量的增加,Zn1Al1Mg2.5Mn合金中的Al-Mn析出相为Al_(8)Mn_(5)和Al_(0.8)Mn,其中Al_(11)Mn_(4)和Al_(8)Mn_(5)相主要在共晶组织中析出,Al_(0.8)Mn主要在纯锌相内部析出;随着Mn含量的增加,自腐蚀电流密度降低,阻抗值增加,Zn1Al1Mg2.5Mn合金的耐腐蚀性最佳。这是因为Zn1Al1Mg2.5Mn合金中具有六方晶系结构的Al_(0.8)Mn弥散分布在纯锌相中,所产生的析出强化效应使合金的凝固组织更为细化,并且在腐蚀过程中能生成致密的氧化膜,减缓合金镀层的腐蚀速率,因此提高了合金的耐腐蚀性能。

In order to improve the corrosion resistance of hot-dip galvanized products,three types of Zn-Al-Mg alloy ingots with different Mn contents were prepared by induction melting.The compositions were Zn1Al1Mg0.5Mn,Zn1Al1Mg1.2Mn、and Zn1Al1Mg2.5Mn,respectively.And their solidified microstructure and corrosion behavior were analyzed.The results show that the predicted types of Al-Mn compounds are Al_(11)Mn_(4),Al_(8)Mn_(5)and Al_(0.8)Mn through phase diagram calculations.The Al-Mn precipitates in Zn1Al1Mg0.5Mn and Zn1Al1Mg1.2Mn alloys are Al_(11)Mn_(4)and Al_(8)Mn_(5),respectively.As the Mn content increases,the Al-Mn precipitates in Zn1Al1Mg2.5Mn alloy are Al_(8)Mn_(5)and Al_(0.8)Mn.Al_(11)Mn_(4)and Al_(8)Mn_(5)mainly precipitate at grain boundaries,while Al_(0.8)Mn mainly precipitates inside the pure zinc phase.As the Mn content increases,the self corrosion current density decreases and the impedance value increases,Zn1Al1Mg2.5Mn alloy has the best corrosion resistance.Due to the dispersed distribution of Al_(0.8)Mn with a hexagonal crystal structure in the pure zinc phase,the precipitation strengthening effect generated refines the solidification structure of the alloy,and can generate a dense oxide film during the corrosion process,slowing down the corrosion rate of the alloy coating and improving the corrosion resistance of the Zn1Al1Mg2.5Mn alloy.