Study On Microstructure And Properties Of Mg-Al-Zn-Ni-Gd-Y Soluble Magnesium Alloy

With the rapid development of global industry,the demand for primary energy is increasing year by year.As a kind of clean energy stored in shale strata,shale gas has attracted wide attentions from all countries because of its long mining life,long production cycle and large world savings.The combination of soluble materials and fracturing temporary plugging tools can effectively improve the efficiency of shale gas exploitation.Magnesium alloy is an ideal material for preparing fracturing temporary plugging tools because of its low density,high specific strength,good mechanical processing performance and high chemical activity.Domestic scholars have carried out a series of development work on soluble magnesium alloys.However,in the existing research,there are generally problems such as low mechanical properties,uncontrollable solubility,and high production costs,which cannot meet the needs of 4000-8000 meters deep mining.Therefore,it is of great significance to study the influence of composition design and processing technology on the microstructure and properties of soluble magnesium alloys and the mechanism of action,which plays important role in promoting preparation and application of the soluble magnesium alloys.In this paper,Mg-9Al-1Zn alloy doped with Ni,Gd and Y elements was used as the research object,and the effects of elements(Ni,Gd,Y),extrusion temperature and aging time on the microstructure,mechanical properties and dissolution properties of the magnesium alloy were discussed.On the basis of optimizing the preparation process,a high-performance Mg-9Al-1Zn0.4Ni-0.1Gd-0.05Y soluble magnesium alloy material is prepared.The research results can lay a foundation for the practical application of soluble magnesium alloy materials.The specific research contents and related conclusions are as follows:(1)The effects of alloying elements Ni and Gd on the microstructure,mechanical properties and solubility in KCl aqueous solution of Mg-9Al-lZn-0.05Y alloy were investigated.After the addition of Ni and Gd elements,the elements are preferentially combined with Al,and as a result,needle-like or flower-like Al-Ni-Gd phases form,and then the excess Ni combines with Al to precipitate the granular A13Ni phase,resulting in a decrease in the volume fraction and size of the β-Mg17Al12 phase.With the increase of Ni content,the mechanical properties of the alloy increase first and then decrease,while the solubility increases first and then goes to level off.With the increase of Gd content,the mechanical properties and solubility of soluble magnesium alloys increase first and then decrease.The alloy composition with the best comprehensive performance is Mg-9Al-1Zn-0.4Ni-0.1Gd-0.05Y.The compressive strength of the as-cast alloy is 384 MPa,and the dissolution rate is 2579 mm·y-1.(2)The effects of extrusion temperature on the microstructure,mechanical properties and solubility of Mg-9Al-1Zn-0.4Ni-0.1Gd-0.05Y alloy were clarified.The extrusion can significantly refine the grain size of Mg-9Al-1Zn-0.4Ni-0.1Gd-0.05Y alloy.With the increase of extrusion temperature,the grain size of the alloy increases gradually,whereas the volume fraction of the second phase,the mechanical properties and the solubility decreases simultaneously.The maximum compressive strength can reach 473 MPa,and the maximum solubility can reach 900 mm·y-1.(3)The effect of aging time on the microstructure and properties of as-extruded Mg-9Al1Zn-0.4Ni-0.1Gd-0.05Y alloy was discussed.The Mg-9Al-1Zn-0.4Ni-0.1Gd-0.05Y alloy extruded at 400℃ exists a large number of discontinuous and continuous precipitates after aging treatment.With the prolonging of aging time,the discontinuous precipitation zone gradually covers the continuous precipitation zone.The mechanical property of the alloy reaches its peak after aging treatment at 200℃ for 12 hours,and the responding compressive strength is 586 MPa.While the solubility reaches its peak of 1849 mm·y-1 after aging treatment for 30 hours.(4)The optimum preparation process of Mg-9Al-1Zn-0.4Ni-0.1Gd-0.05Y alloy was determined.The as-cast Mg-9Al-1Zn-0.4Ni-0.1Gd-0.05Y alloy has the best comprehensive properties after forward extrusion at 400℃ and aging treatment at 200℃ for 30h.The compressive strength is 548 MPa and the solubility is 1849 mm·y-1.