The Influence Of ECAP Deformation And Subsequent Extrusion On The Microstructure And Properties Of Mg-Zn-Ca-Mn Magnesium Alloy

Equal channel angular pressing (ECAP) was performed on the as-extruded Mg-5.25wt%Zn-0.6wt%Ca-0.3wt%Mn magnesium alloy at 250℃and 300℃for different passes, with subsequent extrusion at 100℃and 150℃on the ECAPed magnesium alloy. The microstructure of the as-extruded magnesium, ECAPed ultrafine grained magnesium alloy and subsequent extruded alloy were examined by means of optical microscopy (OM), scanning electronic microscopy (SEM) and transmission electron microscopy (TEM). Texture development of as-extruded magnesium alloy, ECAPed magnesium alloy and subsequent extruded alloy were investigated by neutron diffractometer and EBSD. Tensile properties at room temperature and damping behavior of magnesium alloy, ECAPed magnesium alloy and subsequent extruded alloy were investigated and mechanism was discussed.The as-extruded magnesium alloy had an initial grain size of about 4μm, with bands of second phrase parallel to the extrusion direction. During ECAP, the second phrase were broken and dispersed in the matrix and some nano-phrase precipitated from the matrix. After the as-extruded magnesium alloy was subjected to 4-pass ECAP at 250℃, the grain size was refined to about 1.0μm. With repeating passes, the yield stress and the elongation to failure of the alloy increased. After 4-pass ECAP at 300℃, the elongation to failure reached 22.7%, which was two times of that of the as-extruded alloy, with ultimate tensile strength reaching 323.2MPa, which resulted from the grain refinement and texture modification during ECAP.Perform subsequent extrusion at 100℃and 150℃on the ECAPed magnesium alloy. The subsequent extrusion lead to further grain refinement and more homogeneous microstructure. Subsequent extrusion at lower temperature can improve yield stress and hardness of magnesium alloy, while subsequent extrusion at higher temperature can cause a rise to the yield stress and elongation to failure. After 250℃4-pass ECAPed magnesium alloy were extruded at 100℃, grain size was refined to 0.96μm with ultimate tensile strength reaching 356MPa. After 300℃4-pass ECAPed magnesium alloy were extruded at 100℃, its grain was refined to 1.1μm with ultimate tensile strength reaching 334.62MPa, obtaining the elongation to failure of 15.2%. Grain refinement, homogeneous microstructure and texture development during subsequent extrusion gave sire to the result above.