Strong and ductile heat-treatable Mg-Sn-Zn-Al wrought alloys

A newly developed Mg-Sn-Zn-Al based alloy shows substantial strengthening by artificial aging. A Na-doped Mg-5.4Sn-4.2Zn-2.0Al-0.2Mn-0.1Na (TZAM5420-0.1Na) (wt.%) alloy exhibited a significant increase in yield strength from 243 to 347 MPa by a T6 treatment due to the uniform dispersion of nanoscale precipitates by aging. The trace addition of Na causes the formation of Sn-Na co-clusters in the early stage of aging, which provides heterogeneous nucleation sites for Mg2Sn precipitates. However, Na strongly segregates at grain boundaries and this degrades the ductility significantly. To overcome this problem, we developed a Na-free Mg-6.6Sn-5.9Zn-2.0Al-0.2Mn (TZAM6620) alloy, in which nano-scale MgZn2 precipitates are uniformly dispersed by double aging. Pre-aging caused the formation of Zn-rich Guinier Preston zones, which acted as heterogeneous nucleation sites for the MgZn2 precipitates. The double-aged TZAM6620 alloy exhibited a very high yield strength of 370 MPa with large elongation of 14%. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.