Experimental and thermodynamic investigations into the microstructure of laser clad Al-Si coatings on AZ91D alloys

摘要

Al-Si coatings were fabricated on AZ91D magnesium alloys by laser cladding using Al-Si eutectic alloy powders. Microstructure of the coatings was examined by optical microscope (OM), scanning electronic microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD). The phase fractions, phase compositions and solidification process of the coatings were calculated using Thermo-Calc software based on the experimental results. The results show that a dense, crack and porous free coating with good metallurgical bond was obtained. The top part of the coating consists of Mg _2Si dendrites, Al _(12)Mg _(17) matrix and bright needle-like Al _3Mg _2 phase. The bottom part of the coating is formed of dendritic α-Mg solid solution, irregular block Mg _2Si phase and rosette eutectics (α-Mg+Al _(12)Mg _(17)). The calculation results obtained from Thermo-Calc software agree well with the ones from the experiment. It is beneficial to the coating design for desirable microstructural and mechanical properties.