Effect of Three-High Rotary Piercing Process on Microstructure, Texture and Mechanical Properties of Magnesium Alloy Seamless Tube

Mg alloy seamless tubes (MASTs) were prepared through three-high rotary piercing process, effect of billet temperature, feed angle and plug advance on microstructure, texture and mechanical properties of tubes were investigated. The effect on the deformation mechanism and improving mechanical properties mechanism of this process for MASTs were studied. The results show that the grain size could be refined to 11.3–31.1% of the initial grain size and the microstructure was more uniform due to the accumulation of strain. The formation of high strain gradient at the grain boundary activated the non-basal slip. This piercing process could change the grain orientation of as-extruded billet and eliminate the initial basal texture to produce new favorable texture. And the process could accelerate the continuous dynamic recrystallization process. After piercing, yield strength of pierced tubes decreased by 6.7%, ultimate tensile strength (UTS) and elongation increased by 32.4 and 45%, respectively, at optimal parameters. The plate-shaped β₁-Mg₁₇Al₁₂ orientation transformed from basal plates to prismatic plates, facilitating the increase in UTS and ductility. The decrease size of nanoscale precipitates could reduce the cracking possibility. The critical resolved shear stress ratios of pyramidal (10−11) slip and (11−22) slip to basal slip for the sample including prismatic plates both decreased compared to that including basal plates. This could enhance the ductility of tube sample. Moreover, grain boundary sliding could contribute to a better ductility via coordinating deformation and reducing stress concentration during piercing process.