| Magnesium alloys which are thought as a kind of light engineering materials, have a widely utility in the future. At present, AM60 magnesium alloy has become one of the most widely used commercial magnesium alloys due to its high elongation. However, as compared with other magnesium alloys such as AZ91 alloy, the strength of AM60 alloy is relatively low, which results in the limited application of the alloy. Therefore, it is very necessary to improve the properties of AM60 alloy by other methods such as further alloying and/or micro-alloying and heat treatment. It is well known that adding rare-earth elements to magnesium alloys are very beneficial to improve the mechanical properties of magnesium alloys. But up to now, the research about the improvement for the microstructure and mechanical properties of AM60 alloy by rare-earth additions is relatively limited. At the same time, the investigations about the effects of rare-earth alloying and/or micro-alloying on the microstructure and mechanical properties of AM60 alloy are not very systematical and perfect. Therefore, further investigations about rareearth alloying and/or micro-alloying of AM60 alloy have very important significance to improve the properties of AM60 alloy and promote its application.Based on the application of AM60 magnesium alloy in the automobile hub, three rareearth alloying and/or micro-alloying elements, Nd, Ce and Sc, were chosen for AM60 magnesium alloy in the paper, and then the effects of the three elements and heat treatment on the microstructure and mechanical properties of the AM60(Mg-6Al-0.55Mn) magnesium alloy were investigated by using optical microscope(OM), scanning electron microscope(SEM) and EDS analysis, X-Ray diffraction(XRD), differential scanning calorimetry(DSC) and tensile properties testing. And the following main results were obtained:1) The as-cast microstructure of the AM60 magnesium alloy mainly consists of α-Mg, Mg17Al12 phases with layer- and bone-like shapes, and Al-Mn phase with small amount, thereinto most Mg17Al12 phases mainly distribute at the grain boundaries in the form of the continuous and/or quasi-continuous nets.2) After adding 1.0 wt.% Nd to the AM60 magnesium alloy, the amount of the Mg17Al12 phase in the microstructure of the alloy obviously decreases and its size also decreases, at the same time, the rod-like Al11Nd3 phases are also observed. Furthermore, an increase in Nd amount from 1.0 wt.% to 2.0 wt.% causes the amount and size of the Mg17Al12 phase to gradually decrease but results in the amount of the Al11Nd3 phase to gradually increase. At the same time, adding 1.0-2.0 wt.% Nd to the AM60 alloy can obviously improve the as-cast tensile properties at room temperature(RT) for the alloy, thereinto the best improvement is obtained by adding 1.5 wt.% Nd. In addition, T4(410℃×32h + water quenching) and T6(410℃×32h + water quenching and then 200℃×20h + air cooling) can also improve the tensile properties of the AM60 alloys with and without Nd addition, thereinto the efficiency of T6 treatment is relatively higher than T4 treatment, but the elongation of the T6-treated AM60 alloy without Nd is relatively poorer than that of the T4-treated alloy. Amongst the heat-treated AM60 alloys without Nd addition and with 1.0-2.0 wt.% Nd, the heat-treated alloy with 1.5 wt.% Nd has the relatively optimum tensile properties at RT.3) After adding 1.0 wt.% Ce to the AM60 magnesium alloy, the amount of the Mg17Al12 phase in the microstructure of the alloy obviously decreases and its size also decreases, at the same time, the rod-like Al11Ce3 phases and the particle-like Al10Ce2Mn7 phases with small amount are also observed. Furthermore, an increase in Ce amount from 1.0 wt.% to 2.0 wt.% causes the amount and size of the Mg17Al12 phase to gradually decrease but results in the amount of the Al11Ce3 phase to gradually increase. At the same time, adding 1.0-2.0 wt.% Ce to the AM60 alloy can obviously improve the as-cast tensile properties at RT for the alloy, and an increase in Ce amount from 1.0 wt.% to 2.0 wt.% causes the tensile strength, yield strength and elongation to gradually increase. In addition, T4(410℃×32h + water quenching) and T6(410℃×32h + water quenching and then 200℃×20h + air cooling) can also improve the tensile properties of the Ce-containing AM60 alloys, thereinto the improved efficiency of T6 treatment for the tensile strength and yield strength is relatively higher than T4 treatment, but the elongation of the T6-treated alloys are relatively poorer than that of the T4-treated alloys. Amongst the heat-treated AM60 alloys without Ce addition and with 1.0-2.0 wt.% Ce, the heat-treated alloy with 2.0 wt.% Ce has the relatively optimum tensile properties at RT.4) After adding 0.15 wt.% Sc to the AM60 magnesium alloy, the particle-like Mg17Al12 phases with large amount are observed, and the fine Mn2 Sc and Al3 Sc phases are also found in the microstructure of the alloy. At the same time, an increase in Sc amount from 0.15 wt.% to 0.45 wt.% causes the amount of the Mg17Al12 phase to gradually decrease. Furthermore, adding 0.15-0.45 wt.% Sc to the AM60 alloy can obviously improve the as-cast tensile properties at RT for the alloy, thereinto the best improvement is obtained by adding 0.30 wt.% Sc. In addition, T4(410℃×32h + water quenching) and T6(410℃×32h + water quenching and then 200℃×20h + air cooling) can also improve the tensile properties of the Sc-containing AM60 alloys, thereinto the improved efficiency of T6 treatment is relatively higher than T4 treatment. Amongst the heat-treated AM60 alloys without Sc addition and with 0.15-0.45 wt.% Sc, the heat-treated alloy with 0.15 wt.% Sc has the relatively optimum tensile properties at RT.5) Among the three alloying and/or micro-alloying elements of Nd, Ce and Sc, the improvement of the tensile properties at RT for the AM60 magnesium alloy with minor Sc addition is relatively optimum, thereinto the as-cast AM60 alloy with 0.30 wt.% Sc has the highest tensile properties at RT and the T4- and T6-treated AM60 alloys with 0.15 wt.% Sc exhibit the highest tensile properties at RT. |
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