Effect Of Bi On Microstructure And Mechanical Properties Of Mg-3Al-3Nd Alloy

Due to its high specific strength,excellent corrosion resistance,biocompatibility and good heat resistance,magnesium rare earth alloy has attracted more and more attention at home and abroad.In order to further improve the microstructure and high-temperature mechanical properties of Mg-Al-RE system alloy,researchers at home and abroad improve the heat resistance of existing heat-resistant magnesium alloy by adding alkaline earth metal AE?Ca,Sr,Ba?or the fourth,fifth group elements?Sn,Pb,Bi,sb?.The price of these elements is relatively low,which is one of the main directions of developing new low-cost heat-resistant magnesium alloy in the future.In this paper,a new idea is proposed to optimize the properties of rare earth magnesium alloy by using Bi element with lower cost.According to a large number of previous research work of our research group,Mg-3Al-3Nd alloy with better structure and mechanical properties was selected.Firstly,the influence of Bi on the microstructure and mechanical properties of Mg-3Al-3Nd-xBi alloy was studied systematically.The results show that Bi can refine the microstructure of as-cast Mg-3Al-3Nd alloy,and the grain size of as-cast Mg-3Al-3Nd alloy without Bi is 1854?m.with the increase of Bi content,the grain size of as-cast Mg-3Al-3Nd alloy decreases sharply.When the Bi content is 1wt%,the grain size is the smallest,which is 890?m.with the further increase of Bi content,the grain size increases.The Mg-3Al-3Nd alloy is mainly composed of acicular Al₁₁Nd₃ phase and Al₂Nd phase.After adding Bi element,the granular bind phase appears.With the increase of Bi element,the number of granular bind phase increases,and acicular Al₁₁Nd₃ phase increases The mechanical properties of Mg-3Al-3Nd-xBi alloy at room temperature and high temperature can be improved by adding Bi.When Bi content reaches 1wt%,the tensile strength and elongation of Mg-3Al-3Nd-xBi alloy at room temperature,150?,175?,200?and 225?reach the maximum value,and the mechanical properties of Mg-3Al-3Nd-xBi alloy decrease with the increase of Bi content Compared with Mg-3Al-3Nd alloy,adding Bi can improve the hardness of the as-cast alloy.When the Bi content is 1wt%,the as cast Vickers hardness reaches the maximum value of85.3HV.With the Bi content further increasing,the as cast hardness of the alloy decreases.Then,the effect of Bi on the microstructure and mechanical properties of the extruded Mg-3Al-3Nd-xBi alloy was investigated.The results show that compared with the grain size of as-cast Mg-3Al-3Nd-xBi alloy,the grain size of the extruded Mg-3Al-3Nd-xBi alloy greatly decreases.Without Bi,the grain size of the extruded Mg-3Al-3Nd alloy is 14?m.with the increase of Bi content,the grain size of the extruded Mg-3Al-3Nd alloy decreases When the content of Bi is1wt.%,the grain size of extruded Mg-3Al-3Nd-xBi alloy is the smallest,which is11.44?m.with the further increase of Bi content,the grain size of extruded Mg-3Al-3Nd alloy increases.The mechanical properties of extruded Mg-3Al-3Nd-xBi alloy at room temperature and high temperature can be improved by the addition of Bi.When the content of Bi reaches 1wt.%,the tensile strength and elongation of extruded Mg-3Al-3Nd-xBi alloy reach the maximum at room temperature,150?,175?,200?and 225?,and with the increase of Bi content,the mechanical properties of Mg-3Al-3Nd-xBi alloy decrease;the high temperature mechanical properties of Mg-3Al-3Nd-xBi alloy are similar to those of as-cast alloy with the change of strain rate,the high temperature tensile strength of Mg-3Al-3Nd-xBi alloy increases with the increase of strain rate,and the elongation decreases with the increase of strain rate;compared with Mg-3Al-3Nd alloy,the addition of Bi can improve the mechanical properties of Mg-3Al-3Nd-xBi alloy When the Bi content is 1wt%,the as-extruded Vickers hardness reaches the maximum value of 78HV.With the increase of Bi content,the extruded hardness decreases.