Preparation,Structure And Properties Of Rare Earth Magnesium Alloys Containing LPSO Structure

Magnesium alloy has a low density,high specific strength,has good casting and machining properties.It is considered to be an ideal metal structural material and is widely used in the aerospace,automotive,and power industries.The rare earth magnesium alloy has excellent room temperature mechanical properties,and the rare earth element has a high solid solubility in magnesium,and can obtain excellent solid solution strengthening and aging strengthening effects.Therefore,rare earth magnesium alloys provide great potential for solving the contradiction between mechanical properties and damping properties of magnesium alloys.In this paper,the rare earth magnesium alloy containing LPSO structure was prepared by smelting process,and its solution and aging treatment were carried out to study its effect on the microstructure and properties of rare earth magnesium alloy.Four-component as-cast Mg-6Gd-2xY-xZn-0.6Zr（x=0.5,1,1.5,2,wt%）alloys were prepared using a smelting process.With the increase of Y and Zn contents,the grains became fine and the size of the second phase gradually increased.The addition of LPSO phase can significantly improve the mechanical properties of rare earth magnesium alloys.The Mg-6Gd-3Y-1.5Zn-0.6Zr（wt%）alloy has the best comprehensive mechanical properties（tensile strength 216.64MPa,elongation12.9%）,and damping performance is also better.The grain size of Mg-6Gd-3Y-1.5Zn-0.6Zr alloy increases gradually with the increasing of solution temperature.The solution treatment and aging treatment at different time have no obvious effect on the grain size of the alloy,and the original18R-LPSO structure in Mg-6Gd-3Y-1.5Zn-0.6Zr alloy transforms to 14H-LPSO after high temperature heat treatment.Hardness peak of Mg-6Gd-3Y-1.5Zn-0.6Zr alloy agedat 200°C for4h,and theagingprecipitation sequence of Mg-6Gd-3Y-1.5Zn-0.6Zr alloy is:α-Mg（SSSS）→β"→β’→β₁（fcc）→β.In the Mg-6Gd-3Y-1.5Zn-0.6Zr alloy,the main aging precipitating strengthening phase is aβ-phase of"丫"type oriented along the{101^-0}_αof the Mg-based plane.The LPSO structure has an important influence on the mechanical properties of rare earth magnesium alloys.After the solution treatment and aging treatment,the tensile strength of the post-alloy is improved,after 520°C solution treatment for 10h,the maximum tensile strength reaches 225MPa,and the yield strength has no obvious change,but the plasticity is reduced.The fracture mechanism of as-cast alloys changes from brittle fracture to quasi-cleavage fracture.After solution treatment and aging treatment,the alloy shows quasi-cleavage fracture with a small amount of ductile fracture.LPSO-containing rare earth magnesium alloys have good damping properties.The Mg-6Gd-3Y-1.5Zn-0.6Zr alloy after solution treatment at 500°C for 15 h has the best strain damping performance(Q^-1=0.025,ε=2×10^-3).The strain-damping mechanisms of solid-state and as-cast Mg-based Mg alloys are all in line with the G-L theory.The existence of the LPSO structure may serve as a new damping source and thus affect the damping properties of the alloy.A recrystallization damping peak P2 of about 250°C was observed in the as-cast four-component rare earth magnesium alloys.The Mg-6Gd-3Y-1.5Zn-0.6Zr alloy solution treated at different temperatures has a relaxation-type damping peak P1 at 50-150°C.According to the analysis of the activation energy of rare earth magnesium alloy at high temperature,With the increase of solid solution time,the atoms need more energy to diffuse.