工艺状态对Mg-5Al-0.4Mn-1.6Ca镁合金组织和性能的影响

Influence of different states on the microstructure and properties of Mg-5Al-0.4Mn-1.6Ca alloy

采用金相显微镜、万能试验机和电化学工作站测试了不同加工状态(铸态、均匀化态、挤压态)的Mg-5Al-0.4Mn-1.6Ca合金组织、力学性能和耐腐蚀性能。结果显示:铸态合金硬度为61.3HV;均匀化处理后合金组织粗大和第二相溶解导致硬度下降,为55.85HV;而挤压后的合金晶粒明显细化,硬度得以提升,为66.43HV。腐蚀性能方面,铸态合金耐腐蚀性能最好,腐蚀电流密度为37.82μA/cm^2;挤压态腐蚀电流密度为56.08μA/cm^2,耐腐蚀性能稍低于铸态合金;均匀化态腐蚀电流密度为215.15μA/cm^2,耐腐蚀性能最差。这主要是由于铸态合金中有大量不连续的(Mg,Al)_2Ca相作为阳极被腐蚀从而保护了镁基体;而均匀化处理之后,第二相溶解于合金基体中导致这种保护作用降低。

The microstructure, mechanical properties and corrosion resistance of Mg-5A1-0.4Mn - 1.6 Ca alloys with different states （ as - cast, as - homogenized and as - extruded） were investigated by optical microscopy, uniaxial tensile and electrochemical workstation. Results showed that the hard- ness of as - cast alloy was 61.3HV. After homogenization treatment, the microstructure of alloy became coarse and the second phases were dissolved in the matrix, which lead to the decline of the hardness of 55.85HV. As the extrusion deformed, the grains of alloy refined and the hardness improved to 66. 43 HV. In corrosion resistance, the as - cast alloy had the best corrosion resistance, which had the corrosion current density of 37. 82μA/cm2. The as - extruded alloy which had the corrosion current density of 56.08μA/cm2 showed the lower corrosion resistance and the as - homogenized alloy （215. 15μA/cm2） was the worst. The best corrosion resistance of as - cast alloy was mainly attributed to the massive and discontinuous （Mg, Al）2Ca phase, which acted as an anode to protect the α - Mg matrix. After homogenization treatment, dissolution of second phase led to the decrease of the protective effect.