The Research Of Preparation Technique And Application Of Mg-Sr Preliminary Alloy

There are distinct advantages,such as lower density ,specific strength and specific stiffness, higher damping, strongly shielding ability of electromagnet,and easier recycling,to lightweight magnesium in powertrain components where large die-cast components are used in automotive applications ,industry of Aero-Space,and industry of electron, especially in automobile. The sizes of crystalline grains affect the mechanics properties of the magnesium alloys. It is one of the main methods of refining the grains that the additive of modification was added into magnesium alloys. Sr and Sr alloys have been applied to Mg or Al alloys as an additive of modification. In recent years, Al-Sr and Mg-Sr alloy is studied rarely,Mg-Sr alloy has not studied the report yet inland, research in this field is also very rarely abroad. In this papers, the preparation technologies of Mg-Sr alloys which were prepared by melt-leaching-reduction process and Mixture method respectively, and the difference of their composition were analyzed, on which of the basis, the effect of process parameters on morphology of the structure, composition ,and distribution were emphasly studied. at the same time ,the effect of the value of Sr/Al on the morphology of Mg-Al-Sr ternary alloys and that of magnesium-strontium alloys on the structure and the mechanics properties of AZ91 were also studied., in addition, the feasibility of Mg-Sr alloys prepared by melt-leaching-reduction process and the reason that is not to adopt SO₂ gas as protecting gas in the course of the preparation were studied according to thermodynamics theory. Moreover, the experimental result were studied by X fluorescence analysis, Scanning electron microscope (SEM) , X ray diffraction appearance (XRD ),Optics microscope (OM ),etc. The results are shown that: â‘ the morphology of magnesium-strontium alloy was network structure,and the laminary eutectic morphology distributed at the grain boundary or in the interdendritic regions. â‘¡The holding temperature was too hight or too low ,the holding time was too long or too short ,which both reduced the amount of dissolved strontium ,affecting the percentage of eutectic structure and the size of grain .The effect of strontium on the grain size of Mg-Sr alloy was measured by the value of GRF(the ability of the grain boundary partial gathering) Which depended on the original concentration of strontium. the GRF value increased with the increasing original concentration of strontium,which contributed to improve the ability of refining grain.â‘¢Using the argon gas as protective gas ,the content of Sr in alloy was more than that of alloy made by the flux method. â‘£The organization and composition of Mg-Al-Srternary alloy were relation to the value of Sr/Al. as the value increasing,the second phase Al4Sr was gradually changed into Mg17Al12,Mg-Al-Sr ternary compound,and Al4Sr. ⑤the Mg-Sr alloy prepared by melt-leaching-reduction process,in which the actual content of Sr was too low ,and the grain of alloy was relative large. It is the first to find that SrCO3 , as an additive ,can refine the grain of magnesium or magnesium alloys during the research work. â‘¥Mg-Sr alloy had the function of refining the grain of AZ91 alloy,but its effect on the mechanics properties of AZ91 was slightly, because Mg-Sr and Al-Sr brittle phases distributed at the grain boundary. the function of refining of magnesium-strontium alloy depended on the amount of added Sr. when the amount of Mg-Sr alloy was added to about 0.6%, The value of tensile strength and degree of hardness were maximum .if the mount of Mg-Sr alloy continue increased , the mechanics properties of AZ91 alloy would be deteriorated.