Microstructure change of AZ91 magnesium alloy surface melted by laser

In order to study the surface tissue variation of the magnesium alloy treated by laser,the surface of AZ91 magnesium alloy was treated by CO2 laser under the protection of helium gas.The treated workpiece was observed through optical microscope,and the microhardness value of the cross section was tested by microhardness tester.The result of the experiment showed that the grain size of the treated magnesium alloy was refined to the primitive magnesium alloy,the grain size of the magnesium alloy becoming smaller with the decrease of the scanning speed,and that the β phase along the grain boundary decreased distinctly.The microhardness test of the cross section showed that the microhardness value of the treated section enhanced distinctly,and the smaller of the grain size,the harder of the cross section,according to the Hall-Petch formula.