The microstructure evolution and age-hardening response for different Sm/Sn ratios(0-2.55,in wt.%)of Mg-Sn-Sm alloys were investigated.The second phase formation in as-cast alloys and the Mg_(3)Sm precipitates formed ...The microstructure evolution and age-hardening response for different Sm/Sn ratios(0-2.55,in wt.%)of Mg-Sn-Sm alloys were investigated.The second phase formation in as-cast alloys and the Mg_(3)Sm precipitates formed in aged alloys were characterized using XRD,FESEM and HAADF-STEM with EDS techniques.Results indicate that the Sm/Sn ratio has a great influence on the phase constitution,α-Mg grain size and age-hardening response.With the increment of Sm/Sn ratio,Mg_(41)Sm_(5) and thermally stable MgSnSm phases precipitate.When the Sm/Sn ratio is about 1.19,the secondary dendrite arm spacing ofα-Mg grains significantly decreases.Furthermore,the alloy with Sm/Sn ratio up to 2.55 exhibits the highest age-hardening response,the hardness value increases from 52 HB at solution-treated condition to 74 HB at peak-aged condition(ageing at 220 ℃ for a short time of 4 h).This is attributed to the large volume fraction of needle-like Mg_(3)Sm precipitates formed in theα-Mg matrix during ageing treatment,which results in a significant precipitation strengthening effect.展开更多
The effect of Sn, Ca, Al, Si and Zn addition on the compressive strength of cast Mg-Sn-Ca （TX） alloys was studied in the temperature range of 25-250 °C and correlated with the microstructure. The Sn to Ca mass ...The effect of Sn, Ca, Al, Si and Zn addition on the compressive strength of cast Mg-Sn-Ca （TX） alloys was studied in the temperature range of 25-250 °C and correlated with the microstructure. The Sn to Ca mass ratio up to 2.5 contributes to the formation of Mg2Ca phase at the grain boundaries and CaMgSn in the matrix, while a ratio of 3 gives only CaMgSn phase mostly in the matrix. While the compressive strength decreases with the increase in temperature, for Sn/Ca up to 2.5, a plateau occurs in 100-175 °C, which is attributed to the strengthening by Mg2Ca. However, for ratio of 3, the strength is lower and decreases more gradually. Mg-3Sn-2Ca （TX32） has the highest strength and the addition of 0.4%Al increases its strength but simultaneous addition of Si lowers the strength. Likewise, the addition of Zn improves its strength but simultaneous addition of Al slightly decreases the strength. The results are correlated with the types of intermetallic phases that form in various alloys.展开更多
The stability of underground excavations has become an important issue in order to extend underground mining operations and extract deeper deposits. The increasing demand for Tin-Tungsten (Sn-W) for industry and its m...The stability of underground excavations has become an important issue in order to extend underground mining operations and extract deeper deposits. The increasing demand for Tin-Tungsten (Sn-W) for industry and its market price has created a motivation for mining companies to extract deep-seated Sn-W ore deposits in Myanmar. Thus, this paper aims to investigate the stability of underground openings, especially, the stope with considering the mining methods. To meet the objective, FLAC<sup>3D</sup> 5.0 simulation was used for the assessment of stope under different stress ratios, 0.5, 1.0, and 1.5 for two types of underground mines;Open stoping and Cut and Fill stoping. The results show that the risk of instability of stope is high under the stress ratio of <em>K</em> = 0.5 than that of <em>K</em> = 1.0 and <em>K</em> = 1.5 in both mining methods. However, the stability of the stope in open stope method is lower than that of cut-and-fill method obviously. This result shows that the appropriate mining method has to be selected for extraction of Sn-W deposit carefully in terms of the balance of safety and cost.展开更多
基金the Natural Science Foundation of Inner Mongolia under Grant No.2020MS05014the Science and Technology Planning of Inner Mongolia under Grant No.2020GG0318.
文摘The microstructure evolution and age-hardening response for different Sm/Sn ratios(0-2.55,in wt.%)of Mg-Sn-Sm alloys were investigated.The second phase formation in as-cast alloys and the Mg_(3)Sm precipitates formed in aged alloys were characterized using XRD,FESEM and HAADF-STEM with EDS techniques.Results indicate that the Sm/Sn ratio has a great influence on the phase constitution,α-Mg grain size and age-hardening response.With the increment of Sm/Sn ratio,Mg_(41)Sm_(5) and thermally stable MgSnSm phases precipitate.When the Sm/Sn ratio is about 1.19,the secondary dendrite arm spacing ofα-Mg grains significantly decreases.Furthermore,the alloy with Sm/Sn ratio up to 2.55 exhibits the highest age-hardening response,the hardness value increases from 52 HB at solution-treated condition to 74 HB at peak-aged condition(ageing at 220 ℃ for a short time of 4 h).This is attributed to the large volume fraction of needle-like Mg_(3)Sm precipitates formed in theα-Mg matrix during ageing treatment,which results in a significant precipitation strengthening effect.
基金supported by General Research Funds (Projects#115108 and#114809) from the Research Grants Council of the Hong Kong SAR,China
文摘The effect of Sn, Ca, Al, Si and Zn addition on the compressive strength of cast Mg-Sn-Ca （TX） alloys was studied in the temperature range of 25-250 °C and correlated with the microstructure. The Sn to Ca mass ratio up to 2.5 contributes to the formation of Mg2Ca phase at the grain boundaries and CaMgSn in the matrix, while a ratio of 3 gives only CaMgSn phase mostly in the matrix. While the compressive strength decreases with the increase in temperature, for Sn/Ca up to 2.5, a plateau occurs in 100-175 °C, which is attributed to the strengthening by Mg2Ca. However, for ratio of 3, the strength is lower and decreases more gradually. Mg-3Sn-2Ca （TX32） has the highest strength and the addition of 0.4%Al increases its strength but simultaneous addition of Si lowers the strength. Likewise, the addition of Zn improves its strength but simultaneous addition of Al slightly decreases the strength. The results are correlated with the types of intermetallic phases that form in various alloys.
文摘The stability of underground excavations has become an important issue in order to extend underground mining operations and extract deeper deposits. The increasing demand for Tin-Tungsten (Sn-W) for industry and its market price has created a motivation for mining companies to extract deep-seated Sn-W ore deposits in Myanmar. Thus, this paper aims to investigate the stability of underground openings, especially, the stope with considering the mining methods. To meet the objective, FLAC<sup>3D</sup> 5.0 simulation was used for the assessment of stope under different stress ratios, 0.5, 1.0, and 1.5 for two types of underground mines;Open stoping and Cut and Fill stoping. The results show that the risk of instability of stope is high under the stress ratio of <em>K</em> = 0.5 than that of <em>K</em> = 1.0 and <em>K</em> = 1.5 in both mining methods. However, the stability of the stope in open stope method is lower than that of cut-and-fill method obviously. This result shows that the appropriate mining method has to be selected for extraction of Sn-W deposit carefully in terms of the balance of safety and cost.
