Mg-Nd-Zn-Zr合金表面激光熔覆Al-Si/Al2O3复合涂层研究

Study on laser cladding of a Mg-Nd-Zn-Zr Mg alloy with Al-Si/Al2O3 powders

摘要:

本文采用激光熔覆Al-Si/Al2O3粉体来对Mg-Nd-Zn-Zr镁稀土合金进行表面改性，并对熔覆层的形貌、组织、相组成及性能进行了表征。X射线衍射（XRD）分析和扫描电镜（SEM）观察显示，熔覆层主要由α-Mg、Mg2Si、Mg12Nd以及Al3.21Si0.47或Mg17Al12几种相组成，而Al2O3则大部分聚集在熔覆层和基体之间的界面处。截面硬度测试显示，熔覆层的显微硬度最高值在309HV至475HV之间，是基体硬度（55HV）的5~8倍以上，这主要归结为熔覆层内晶粒细化、固溶强化、增强相的形成以及氧化物颗粒的弥散强化作用。在3.5wt%NaCl水溶液中的电化学测试显示，激光熔覆后的镁合金腐蚀电位上升，腐蚀电流密度可由基体的1.683×10-4A/cm2下降至激光熔覆后的0.843×10-5A/cm2，表明激光熔覆后样品表面的腐蚀性能也得到显著提高。

Abstract:

In this paper, laser cladding of Al-Si/Al2O3 powders was applied on a Mg-Nd-Zn-Zr magnesium rare earth alloy, and the microstructure, phase components and properties of the clad layers were carefully characterized. X ray diffraction (XRD) analyses and scanning electron microscope (SEM) observations show that the clad layer is mainly consisted of α-Mg, Mg2Si, Mg12Nd and Al3.21Si0.47 or Mg17Al12 phases. However, Al2O3 particles agglomerate at the bottom of the clad layer close to the melt-substrate interface. The cross section microhardness tests reveal that the maximum hardness of the clad layer ranges from 309HV to 475HV, about 5 to 8 times higher than that of the Mg-Nd-Zn-Zr alloy (55HV) substrate. Such an increased hardness is attributed to the grain refinement, the solution strengthening, the formation of hardening phases and the dispersion strengthening from oxide particles. According to the potentiodynamic polarization measurements carried out in the 3.5wt% NaCl water solution, the corrosion potential of the alloy increased after laser cladding, while the corrosion current density decreased from 1.683×10-4(A/cm2)for the Mg alloy substrate to 0.843×10-5(A/cm2)for the laser clad alloy. Therefore, the corrosion resistance of Mg-Nd-Zn-Zr alloy can also be significantly improved by laser cladding with Al-Si/Al2O3 powders.