Effects of Zn Additions on the Room Temperature Formability and Strength in Mg-1.2Al-0.5Ca-0.4Mn Alloy Sheets

We investigated the effects of Zn additions on the mechanical properties and microstructure of Mg-1.2Al-0.5Ca-0.4Mn and Mg-1.2Al-0.5Ca-0.4Mn-1.6Zn (wt %) alloy sheets fabricated by twin-roll casting and conventional hot rolling. The room temperature stretch formability of the solution-treated alloy sheet is improved by the addition of Zn. The Mg-1.2Al-0.5Ca-0.4Mn-1.6Zn alloy shows an excellent stretch formability with the larger Index Erichsen value of 8.2 mm due to a weak transverse direction split texture. The development of the weak texture is attributed to the uniform grain growth by the solute segregation to the recrystallized grain boundaries. Subsequent bake-hardening treatment, 2% pre-strain at 170 degrees C for 20 min leads to substantial increase in strength without the loss of ductility. The bake-hardened Mg-1.2Al-0.5Ca-0.4Mn-1.6Zn alloy exhibits a high tensile yield strength of 235 MPa with an elongation to failure of 27.1%.