•Minor Ca additions can refine the grains of the Mg–4Y–1.2Mn–1Zn alloy.•Minor Ca addition can improve the tensile properties of the Mg–4Y–1.2Mn–1Zn alloy.•Minor Ca addition can improve the creep properties of the Mg–4Y–1.2Mn–1Zn alloy.•Minor Ca addition can increase the thermal stability of the Mg12YZn phase.The effects of minor Ca addition on the as-cast microstructure and mechanical properties of the Mg–4Y–1.2Mn–1Zn (wt.%) alloy were investigated by using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The results indicate that adding 0.3–0.9 wt.%Ca to the Mg–4Y–1.2Mn–1Zn alloy does not cause an obvious change in the morphology and distribution for the Mg12YZn phase in the alloy. However, the grains of the Ca-containing alloys are effectively refined, and an increase in Ca amount from 0.3 wt.% to 0.9 wt.% causes the grain size to gradually decrease. In addition, adding 0.3–0.9 wt.%Ca to the Mg–4Y–1.2Mn–1Zn alloy can effectively improve the tensile and creep properties. Among the Ca-containing alloys, the alloys with the additions of 0.6 and 0.9 wt.%Ca exhibit the relatively optimum tensile and creep properties. The improvement in the tensile and creep properties for the Ca-containing alloys is possibly related to the grain refinement and higher thermal stability of the Ca-containing Mg12YZn phases in the alloys, respectively.

•Minor Ti additions can refine the primary grains of the Mg–3Sn–2Sr alloy.•Minor Ti addition can modify and refine the primary SrMgSn phase in the Mg–3Sn–2Sr alloy.•Minor Ti addition can improve the tensile and creep properties of the Mg–3Sn–2Sr alloy.In this paper, the effects of minor Ti addition (0.1–0.3 wt.%) on the as-cast microstructure and mechanical properties of Mg–3Sn–2Sr (wt.%) magnesium alloy are investigated. The results indicate that the Mg–3Sn–2Sr alloy is mainly composed of α-Mg, primary and eutectic SrMgSn, and Mg2Sn (with small amount) phases. After the additions of 0.1–0.3 wt.% Ti to the Mg–3Sn–2Sr alloy, the formation of the primary and eutectic SrMgSn phases is suppressed and promoted, respectively. At the same time, the coarse needle-like primary SrMgSn phases are modified and/or refined, and the primary grains are also effectively refined. However, an increase in Ti amount from 0.1 wt.% to 0.3 wt.% does not have obvious effect on the primary grain size of the Ti-containing alloys. In addition, the additions of 0.1–0.3 wt.% Ti to the Mg–3Sn–2Sr alloy can simultaneously improve the tensile and creep properties of the alloy. However, an increase in Ti amount from 0.1 wt.% to 0.3 wt.% does not have obvious effects on the tensile and creep properties of the Ti-containing alloys.

In this paper, the as-cast microstructures, tensile and creep properties of Mg–3.8Zn–2.2Ca–xGd (x=0, 0.36, 0.88, 1.49 and 2.52 wt%) magnesium alloys are investigated and compared. The results indicate that the additions of 0.36–2.52 wt%Gd to the Mg–3.8Zn–2.2Ca ternary alloy can refine the grains of the alloy, and an increase in Gd content from 0.36 wt% to 2.52 wt% causes the grain size to gradually decrease. Furthermore, the additions of 0.36–2.52 wt%Gd to the Mg–3.8Zn–2.2Ca ternary alloy can also improve the tensile properties of the alloy, and the alloy with the addition of 1.49 wt%Gd exhibits the best tensile properties. In addition, the additions of 0.36–2.52 wt%Gd to the Mg–3.8Zn–2.2Ca ternary alloy do not change the creep mechanism of the alloy. However, the creep properties of the Gd-containing alloys are improved, and an increase in Gd content from 0.36 wt% to 2.52 wt% causes the creep properties to gradually increase. Amongst the Gd-containing alloys with the additions of 0.36 wt%, 0.88 wt%, 1.49 wt% and 2.52 wt%Gd, the alloy with the addition of 1.49 wt%Gd exhibits the relatively optimal tensile and creep properties.

The effects of minor Zr and Sr on the as-cast microstructure and mechanical properties of the Mg-4Y-1.2Mn-1Zn (wt.%) alloy were investigated using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The microstructural results indicate that small additions of Zr and/or Sr to the Mg-4Y-1.2Mn-1Zn alloy do not cause an obvious change in the morphology and distribution of the Mg12YZn phase in the alloy. The tensile and creep tests indicate that, although small additions of Zr and/or Sr to the Mg-4Y-1.2Mn-1Zn alloy do not have obvious effects on the creep properties of the alloy, the tensile properties at room temperature and 300 °C for the alloys added with Zr and/or Sr are improved. Among the Zr- and/or Sr-containing alloys, the alloy specifically added with of 0.5 wt.% Zr + 0.1 wt.% Sr obtains the optimum tensile properties, and is followed by the alloys added with 0.5 wt.% Zr and 0.1 wt.% Sr.

The effects of minor Zr, Sr and Ca additions on the microstructure and tensile properties of the as-cast and T5-treated Mg–5Gd–1.2Mn–0.4Sc (wt%) alloys were investigated and compared. The results indicate that adding 0.5 wt%Zr, 0.1 wt%Sr or 0.3 wt%Ca can refine the grains of the as-cast alloy. Among the three additions, the addition of 0.5 wt%Zr obtains the highest grain refining efficiency and followed by the additions of 0.3 wt%Ca and 0.1 wt%Sr, respectively. Furthermore, adding 0.3 wt%Ca is beneficial to the precipitation of Mg5Gd and Mn2Sc phases during T5 heat treatment of the alloy. In addition, adding 0.5 wt%Zr, 0.1 wt%Sr or 0.3 wt%Ca can also improve the tensile properties of the as-cast and T5-treated alloys. Among the three additions, the addition of 0.5 wt%Zr obtains the relatively highest tensile properties and followed by the additions of 0.3 wt%Ca and 0.1 wt%Sr, respectively.Highlights► Minor Zr, Sr and Ca additions can refine the grains of the Mg–5Gd–1.2Mn–0.4Sc alloy. ► Minor Zr addition can improve the tensile properties of the Mg–5Gd–1.2Mn–0.4Sc alloy. ► Minor Sr addition can improve the tensile properties of the Mg–5Gd–1.2Mn–0.4Sc alloy. ► Minor Ca addition can improve the tensile properties of the Mg–5Gd–1.2Mn–0.4Sc alloy.

At present, the mechanical properties of the Mg–3Sn–2Ca magnesium alloy are not satisfying and further enhance needs to be considered via further alloying/microalloying additions. The effects of Zr addition on the as-cast microstructure and mechanical properties of the alloy were investigated by using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The results indicate that adding 0.41, 0.76 or 1.18 wt.% Zr can refine the grains of the alloy, and the primary CaMgSn phases in the Zr-containing alloys are changed from coarse needle-like net to relatively fine short block and/or particle-like shapes. As a result, the tensile and/or creep properties of the Zr-containing alloys are improved. Among the Zr-containing alloys, the alloy with the addition of 0.76 wt.% Zr exhibits the relatively optimum mechanical properties.Research highlights► Adding 0.41–1.18 wt.%Zr can refine the grains of Mg–3Sn–2Ca alloy. ► Adding 0.41–1.18 wt.%Zr can modify the primary CaMgSn phase of Mg–3Sn–2Ca alloy. ► Adding 0.41–0.76 wt.%Zr can improve the mechanical properties of Mg-3Sn-2Ca alloy.

The effects of Sn addition on the as-cast microstructure, mechanical properties and casting fluidity of the ZA84 magnesium alloy are investigated. The results indicate that adding 0.5–2.0 wt.%Sn to the ZA84 alloy not only can result in the formation of Mg2Sn phase but also can refine the Mg32(Al, Zn)49 phase and suppress the formation of Mg32(Al, Zn)49 phase, and with the increase of Sn amount from 0.5 wt.% to 2.0 wt.%, the morphology of Mg32(Al, Zn)49 phase gradually changes from coarse continuous and/or quasi-continuous net to relatively fine quasi-continuous and/or disconnected shapes. In addition, adding 0.5–2.0 wt.%Sn to the ZA84 alloy can improve the tensile and creep properties, and casting fluidity of the alloy. Among the Sn-containing ZA84 alloys, the ZA84 alloy added 1.0 wt.%Sn exhibits the best ultimate tensile strength, elongation and casting fluidity while the ZA84 alloy added 2.0 wt.%Sn has the best yield strength and creep properties.

The effects of minor Sr additions on the as-cast microstructure and mechanical properties of the ZA84 magnesium alloy were investigated. The results indicate that adding 0.05-0.15 wt.% Sr to the ZA84 alloy does not cause an obvious change in the morphology and distribution of the Mg32(Al,Zn)49 phase. However, the grains of the Sr-containing ZA84 alloys are effectively refined. Among the Sr-containing ZA84 alloys, the grains of the alloy added 0.10 wt.% Sr are relatively finer than other alloys. Furthermore, adding 0.05-0.15 wt.% Sr to the ZA84 alloy improves the tensile properties at room temperature and 150 °C but decreases the creep properties. Among the Sr-containing ZA84 alloys, the alloy added 0.10 wt.% Sr obtains the optimum tensile properties at room temperature and 150 °C.

In this paper, the effects of Ce, Sn and Gd additions on the as-cast microstructure and mechanical properties of Mg–3.8Zn–2.2Ca (wt%) magnesium alloy are investigated and compared. The results indicate that adding 1.0 wt% Ce, 1.0 wt% Sn or 1.0 wt% Gd can effectively refine the grains of the Mg–3.8Zn–2.2Ca alloy, and the refinement efficiency of Ce addition is relatively high, followed by the additions of Sn and Gd, respectively. Accordingly, the tensile properties of the as-cast Mg–3.8Zn–2.2Ca alloy are improved by the additions of Ce, Sn or Gd, with the improvement resulting from the Ce addition being best and followed by the additions of Sn and Gd, respectively. In addition, adding 1.0 wt% Ce, 1.0 wt% Sn or 1.0 wt% Gd to the Mg–3.8Zn–2.2Ca alloy can also improve the creep properties of the as-cast alloy. Among the Ce-, Sn- and Gd-containing alloys, the creep properties of the Sn- and Gd-containing alloys are similar but lower than that of the Ce-containing alloy.

The effect of Ca addition on the as-cast microstructure and creep properties of Mg-5Zn-5Sn magnesium alloy was investigated. The results indicate that adding 1.0 wt.% Ca to Mg-5Zn-5Sn alloy can effectively refine the as-cast microstructure of the alloy, and the CaMgSn phase with high thermal stability is formed in the alloy. In addition, adding 1.0 wt.% Ca to Mg-5Zn-5Sn alloy can also improve the creep properties of the alloy. After adding 1.0 wt.% Ca to Mg-5Zn-5Sn alloy, the second creep rate of the alloy at 150°C and 50 MPa for 100 h decreases from 4.67 × 10−8 to 1.43 × 10−8 s−1. The strengthening mechanism is mainly attributed to the microstructural refinement and the formation of CaMgSn phase.