Influence of initial texture on the shock property and spall behavior of magnesium alloy AZ31B

Abstract

In this work, flyer plate impact experiments are conducted on a commercially available magnesium alloy, AZ31B. Equal channel angular pressing (ECAP) process is an established procedure for fabrication of ultra-refined grain structures in metals and alloys. The microstructure of commercially available AZ31B is refined through ECAP process and two sets of specimens with different initial textures and microstructure are considered here. One set of the specimens is machined from a hot rolled AZ31B Mg alloy plate and the others are processed by ECAP of four pass after samples are cut from the initial material. The Hugoniot elastic limit (HEL) and spall strength are determined by analyzing the measured free surface velocity profiles of the specimens. Scanning electron microscope (SEM) is used to observe the microvoids produced along the spall plane and electron back scatter diffraction (EBSD) is employed to examine the twinning distribution on the cross-section of the recovered specimens cutting along the thickness direction. It is found that elastic precursor decay appears in the as-received (without ECAP process) specimens but it is absent in ECAPed specimens. The HEL of the as-received specimens is higher than that of ECAPed specimens over various impact velocities and showed strain rate sensitivity. The spall strength of both sets of specimens is almost identical and enhanced by increasing the impact velocity. The SEM results showed that in the as-received specimens the spall is dominated by coalescence of microvoids emerged along the grain boundaries in a brittle manner. However, in the ECAPed specimens spall was dominated by coalescence of microvoids characterized by inner dimples formation by the pull out of grains in a ductile mode.