Microstructure And Properties Of Mg-Sn Heat-resistant Magnesium Alloy

Magnesium alloy is the most important green engineering material in the world.It has been widely used in the fields of aerospace,automotive and 3C.However,due to its low absolute strength and poor resistance to creep,it limits the widespread use of magnesium alloys in the higher temperature range.The development of a series of low-cost heat-resistant magnesium alloys is of great significance to the application of magnesium alloys.The Sn element has a low price and can form a high melting point,high temperature stable Mg₂Sn phase with Mg.Mg-Sn alloys are expected to become a new generation of heat-resistant magnesium alloy series.However,there are few studies on Mg-Sn heat-resistant magnesium alloys.The microstructures of the two Mg-Sn alloys and their mechanical properties at room temperature and high temperature were investigated by optical microscopy（OM）,scanning electron microscopy（SEM）,X-ray diffraction（XRD）and universal stretching machines.Mg-Si-Sn series alloy was prepared by gravity casting method and Mg-Gd-Y-Sn series alloy was prepared by centrifugal casting method.The main research results are as follows:（1）The as-cast Mg-0.5Si-xSn alloy mainly consists ofα-Mg phase,Mg₂Si phase and Mg₂Sn phase.When Mg contains a small amount of Si,large bulk Mg₂Si phases can be avoided in the alloy.Adding appropriate amount of Sn element can refine the eutectic Mg₂Si structure.Dynamic recrystallization occurs within the Mg-0.5Si-xSn alloy during extrusion.The microstructure of the as-extruded alloy is significantly refined,and the coarse dendritic Mg₂Si compound is broken.（2）The tensile strength of extruded Mg-0.5Si-xSn alloy at room temperature decreases with the increase of Sn,but the yield strength increases with the increase of Sn.The tensile strength of the alloy increases first and then decreases with the increase of Sn element at 200^oC.The Mg-0.5Si-1Sn alloy has the highest tensile strength at room temperature,240 MPa.The maximum tensile strength of Mg-0.5Si-3Sn alloy is 133MPa at 200^oC.（3）Under the centrifugal force,the as-cast Mg-10Gd-3Y-1Sn alloy shows obvious segregation of the compound phase,and the content of compound phase gradually increases with the increase of the centrifugal radius.Grains of as-cast alloys are significantly refined with the increase of centrifugal speed,and the morphology of the compounds changes from small pieces to needles and feathers.（4）The mechanical properties of as-cast Mg-10Gd-3Y-1Sn alloys prepared at different rotational speeds were tested at room temperature.As the rotational speed increases,the strength of the alloys gradually increases.The tensile strength of the alloy reaches 205MPa at 1050r/min,which is 28MPa higher than that of conventional casting.（5）After hot rolling,the as-cast Mg-10Gd-3Y-1Sn alloys with different rotational speeds have grown significantly and twins have appeared.The as-rolled alloys maintained good mechanical properties at both room and elevated temperatures.At300°C,the 700 r/min alloy exhibited the best tensile strength of 296 MPa and good heat resistance.