Development of corrosion-resistant Mg-Al-Ca-Mn-Zn alloy sheet with good tensile properties and stretch formability

To develop high-performance magnesium alloy sheets for sheet applications in the automotive industry, we investigated the effects of the Al content on the tensile properties, stretch formability, and corrosion resistances of Mg-xAl-0.5Ca-0.4Mn-0.8Zn (mass%, x = 2, 5, 8, AXMZx101) alloy sheets. The addition of 5% Al led to the highest limiting dome height of 6.4 mm. The AXMZ5101 alloy sheet also exhibited a good combination of in-plane isotropic strength and ductility. The 0.2% proof stress and elongation to failure were 193 MPa and 24.2% for the rolling direction and 188 MPa and 23.1% for the transverse direction, respectively. Such moderate Al addition resulted in a significantly improved corrosion resistance with a corrosion rate of 0.18 mm/y after immersion in a 3.5% NaCl solution for 7 days, which was approximately 1/4 lower than that of a commercial Mg-Al-Zn alloy sheet. An in-depth characterization revealed that such a good combination of tensile properties and stretch formability is associated with the small grain size, weak basal texture, high work hardenability, and activation of nonbasal slips and that a high corrosion resistance should be achieved by the formation of a dense oxide-rich layer.