Strategic approach to simultaneously enhance strength, formability, and corrosion-resistance synergy of age-hardenable Mg-Zn-Ca-Al-Mn alloy sheet with low Mn content via optimizing Zn and Ca contents

To develop a strong, room-temperature (RT)-formable, and corrosion-resistant Mg alloy sheet, we investigate the age-hardening response, RT formability, tensile properties, and corrosion resistance of low-Mn-containing Mg-(1, 2)Zn-(0.2, 0.5, 1)Ca-0.2Al-0.2Mn (ZXAM, mass%) alloy sheets. The Zn content minimally affects the abovementioned properties. However, the Ca content is important for significantly improving the properties. The addition of ≥ 0.5mass%Ca enhances the RT formability by inclining the (0001) poles toward the transverse direction. Dense corrosion products are formed on the surface of the ≥ 0.5mass%Ca-containing ZXAM alloy sheets, resulting in improved corrosion resistance. Moreover, the aged ≥ 0.5mass%Ca-containing ZXAM alloy sheets exhibit high strength along the rolling direction (RD), in which the 0.2 % proof strength (PS) exceeds 200 MPa. Aging-treatment reduces the corrosion resistance slightly, although the corrosion rates are lower compared with those of commercial wrought Mg alloys. Thereafter, a Mg-2Zn-0.5Ca-0.2Al-0.2Mn alloy sheet simultaneously achieves an excellent combination of strength, RT formability, and corrosion resistance via age-hardening. The PS along the RD and the Index Erichsen value of the sheet reached 213 MPa and 8.7 mm, respectively, and its corrosion rate after immersion in 3.5mass%NaCl solution for 3 days is 3.0 mm･y⁻¹.