Characterization of Mg–9Al–1Zn-0.2Mn alloy tubes processed by a new modified tube cyclic expansion extrusion (M-TCEE) process

Abstract

In this study, a new modified tube cyclic expansion extrusion process named M-TCEE was utilized for producing tubes with ultrafine grained (UFG) microstructure and improved properties. In M-TCEE process, the utilization of a moving mandrel inside the hollow tube during the process provides the possibility of using bulk rod-shaped punch, instead of hollow tubular punch which has been used in conventional TCEE process. This leads to that a higher pressing load can be applied to the material without the risk of punch buckling. So, the production of longer and larger tubes, which needs a higher required pressing load, can be performed easier in M-TCEE process. In current study, the capabilities of M-TCEE process in improving microstructure, mechanical properties and corrosion resistance of the Mg–9Al–1Zn-0.2Mn magnesium alloy tubes were investigated. The results showed that after two passes of M-TCEE process, the yield strength increased from 36 MPa to 137 MPa (3.8 time greater), the ultimate tensile strength increased from 73 MPa to 265 MPa (3.6 time greater) and the ductility was enhanced from 11.2% to 20.2% (1.8 time greater). Three passes of M-TCEE led to improving hardness from 54 HV to 99 HV (1.83 time greater). Also, corrosion results revealed the capability of the M-TCEE process in improving the corrosion resistance of AZ91 tubes. It seems that the M-TCEE process can produce ultrafine-grained AZ91 magnesium alloy tubes with significant mechanical properties and improved corrosion resistance.

Keywords

• Severe plastic deformation
• M-TCEE process
• Mg–9Al–1Zn-0.2Mn alloy
• Mechanical properties
• Ultrafine grained tube