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

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 Mg2Si dendrites, Al12Mg17 matrix and bright needle-like Al3Mg2 phase. The bottom part of the coating is formed of dendritic α-Mg solid solution, irregular block Mg2Si phase and rosette eutectics (α-Mg + Al12Mg17). 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.