Multiple strengthening mechanisms of grain/twin boundaries, dislocations and nanoprecipitates in Mg alloys induced by laser shock processing

Abstract

To investigate the strengthening mechanism for magnesium alloy with gradient nanostructures, magnesium alloy AZ31 with a varying volume fraction of nano gradient structure layers was obtained by using laser shock processing technology and setting parameters such as laser energy and spot size. Macro loading tests for uniaxial tensile and uniaxial compression were carried out, and a microhardness test, metallographic test, and Scanning observations by transmission electron microscope(TEM) and scanning electron microscope(SEM) were carried out. The results show that the tensile and compressive yield strength of the magnesium alloy samples and the microhardness of the matrix are significantly improved, and the volume fraction of the gradient layer has a significant impact on the macromechanical properties. The microstructure of the sample shows abundant grain boundaries(GBs) and twin boundaries(TBs), various dislocation forms, and nanoprecipitates that are dispersed in the crystal. The structural characteristics show that a variety of microstructures exist in a gradient along the thickness direction. The comprehensive analysis shows that the improvement in the macromechanical properties of magnesium alloy samples is the comprehensive result of multiple strengthening, such as grain refinement strengthening, high dislocation density strengthening and nanoprecipitate strengthening.