Study on Laser Cladding NiAl/Al2O3 Coating on Magnesium Alloy

摘要:

利用等离子喷涂技术，在AZ91D镁合金表面制备NiAl/Al2O3涂层，并通过激光对涂层进行重熔处理。利用X射线衍射 (XRD)和扫描电镜 (SEM) 测试手段分别研究了涂层在激光重熔前后的相组成和形貌，涂层的结合强度和孔隙率分别采用拉伸法和光学显微镜 (OM) 测量，利用显微硬度计测量重熔前后涂层的显微硬度。结果表明：经激光重熔处理后，NiAl过渡层与基体及Al2O3涂层界面处出现了具有冶金结合的特征，涂层的结合强度由原来的11.34提高到33.2 MPa；涂层的孔隙率则由原来的10.23%下降到4.10%，涂层变得更致密；涂层中的亚稳相γ-Al2O3全部转变为稳定相α-Al2O3；涂层的显微硬度HV0.05由3290 MPa提高到5200 MPa，有利于其耐磨性的提高

Abstract:

A NiAl/Al2O3 coating was prepared on an AZ91D Mg alloy substrate by laser cladding of the plasma-sprayed coating. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the phases and to study the morphology, respectively. The adhesion strength and the porosity ratio of the coating material were measured by a tensile testing machine and an optical microscope (OM), respectively. The microhardness was measured using a micro Vickers hardness tester. The results show that after laser cladding metallurgical bonding occurrs at the interface between the NiAl transition layer and the substrate. The adhesion strength of the coating increases from 11.34 to 33.2 MPa. The coating became denser and the porosity ratio decrease from 10.23 % to 4.10 %. The metastable γ-Al2O3 phase in the coating without laser cladding is transformed completely into the stable α-Al2O3 phase. The microhardness HV0.05 is improved from 3290 to 5200 MPa, which is beneficial to the wear resistance.