Effect of high-temperature hydrogenation on mechanical properties of a Mg-B4C composite

Abstract

This study aims to understand the influence of high-temperature hydrogenation treatment on the mechanical properties and microstructure evolution of an as-forged Mg-B4C composite containing rare earth elements. During the hydrogenation treatment, a considerable number of (Gd,Y)H2 hydrides with the FCC parameter of a = 0.52 nm were formed in the consumption of Gd and Y solute atoms in the matrix and eutectic Mg24(Gd,Y)5 particles. After hydrogenation treatment, the Mg-B4C composite shows a dramatic decrease in yield strength (from 140 MPa to 94 MPa) and tensile strength (from 220 MPa to 160 MPa), respectively. However, there is a notable increase in elongation (from 4.3 % to 6.6 %). The deterioration of strength in the Mg-B4C composite after hydrogenation treatment can be attributed to grain coarsening, solid solution weakening and a reduction of dislocation density. Meanwhile, the enhancement of ductility in the Mg-B4C composite after hydrogenation treatment can be attributed to the activation of more non-basal dislocations, the presence of smaller dimples, and a decrease in tearing ridges observed after fracture.