Influence of aluminum content on microstructure and performance of Mg-Zn-Ca-Al-Mn magnesium alloys

Abstract

The influences of Al content on microstructure, mechanical properties, stretch formability and thermal conductivity of Mg-1.5Zn-0.3Ca-xAl-0.2Mn (x: 0.2, 0.5, 1, 1.25, 1.5, 2, wt%) alloys were investigated. With increasing the Al content from 0.2 wt% to 2 wt%, the texture changed from the TD-split texture to the quadrupolar texture at the Al content of 1.25 wt%, and finally became the RD-split texture with an increased texture intensity. The change of texture can be attributed to the formation of Al2Ca phase, which weakens the segregation of Ca at grain boundaries due to the decreased amount of Ca solute atoms in the α-Mg matrix. In addition, Al-Mn precipitates changed from a spherical shape to a rod shape accompanied by a largely increased Al/Mn ratio and a decreased amount of precipitates, when the Al content was increased to be larger than 1 wt%. The 0.2–1.5 wt% Al added alloys exhibited excellent stretch formability with the Erichsen values of 8.4–9.1 mm, which were much larger than that (6.8 mm) of the 2 wt% Al added alloy due to texture effect. The 1 wt% Al added alloy had the largest Erichsen value of 9.1 mm, while the 0.2 wt% and 2 wt% Al added alloys exhibited much higher yield strength (165 and 171 vs. 144 MPa). The thermal conductivity continuously decreased with increasing the Al content. Compared to the 2 wt% Al added alloy, the 0.2 wt% Al added alloy exhibited a much higher thermal conductivity (140 vs. 105 W/(m·K)) benefiting from the low concentration of Al solute atoms in the α-Mg matrix. Consequently, a combination of strong mechanical strength, excellent stretch formability and high thermal conductivity was achieved in the low Al-containing alloys with 0.2–0.5 wt% Al.