Research On Microstructures And Properties Of Die Casting Mg-Al-RE Series Alloys

At present,the commercial application of magnesium alloys is mainly realized by die casting.The lightwei ght of key components of new energy vehicles and 5G communication puts forward higher requirements on the mechanical properties and thermal conductivity of magnesium alloy materials.However,the existing magnesium alloy materials cannot fully meet the requirements.Therefore,it is necessary to carry out related studies on new die casting rare earth magnesium alloys with low cost,high strength and high thermal conductivity.In this paper,7 kinds of AZ91 D-xRE series die casting alloys,including AZ91 D-xLa(x=1,2,3wt.%),AZ91 D-xCe(x=1,2,3wt.%)and AZ91D-1Nd,and other 3 kinds of Mg-3.5Al-3RE(RE=La?Ce?Nd)series alloys were prepared by pressure die casting.The microstructures,mechanical properties,thermal conductivity and fluidity of the alloys with different compositions were studied.The effects of different kinds of RE and different contents on the microstructures and properties of Mg-Al-RE series alloys were discussed.The main conclusions are as follows:(1)Microstructures of AZ91D-xLa and AZ91D-xCe alloys are mainly composed of ?-Mg,?-Mg17Al12,Al2RE and Al11RE3;compared with the microstructure of AZ91D alloy,Al11 RE3 and Al2RE phases appear in AZ91 D-xLa and AZ91D-xCe alloys,grains of the alloys are refined,and size of ?-Mg17Al12 phase is decreased.With the increase of RE content,alloys grain refinement,Al2RE and Al11RE3 phases increase in number and size,and the phase size of ?-Mg17Al12 decreases.(2)Compared with AZ91D alloy,the ambient mechanical properties of AZ91D-xLa and AZ91D-xCe alloys are improved.AZ91D-3La alloy shows the best comprehensive tensile mechanical properties,with the UTS,YS and EL of 279 MPa,159 MPa and 8.0%,respectively,they are respectively increased by 17.2%,9.6%and 33.3%compared with AZ91D alloy.The thermal conductivity of the alloys is improved,and a maximum thermal conductivity of 72.2 W/m.K is observed for AZ91 D-2Ce alloy,which is 18.1%higher than that of AZ91D alloy.The fluidity of the alloys is also significantly improved,and fluidity is greatest for AZ91 D-3Ce alloy.(3)Among the AZ91D-1 La,AZ91D-1 Nd and AZ91D-1 Ce alloys,AZ91D-1 Nd alloy shows the best comprehensive tensile mechanical properties at room temperature,with the UTS,YS and EL of 272 MPa,149 MPa and 12.0%,respectively.Compared with AZ91D alloy,they are increased by 14.2%,2.6%and 100.0%,respectively.AZ91D-1Nd alloy also shows the highest thermal conductivity of 69.5 W/m·K;AZ91D-1Ce alloy shows the best fluidity.(4)The mi crostructures of the die casting Mg-3.5 Al-3 RE series alloys are mainly composed of ?-Mg,Al11RE3 and Al2RE.The Mg-3.5Al-3La alloy tends to precipitate Al11RE3 and a few Al2RE phases,and more Al2RE phases are precipitated in Mg-3.5Al-3Ce and Mg-3.5Al-3Nd alloys.The largest phases size and smallest volume fraction of Al11RE3 and Al2RE are observed in Mg-3.5Al-3Nd alloy,whereas phases sizes is the smallest and volume fraction is largest in Mg-3.5 Al-3 La alloy..(5)Among the Mg-3.5Al-3RE series alloys,Mg-3.5Al-3Nd alloy shows the best tensile mechanical properties at room temperature,with the UTS,YS and EL are 251 MPa,138 MPa and 17.0%,respectively.Mg-3.5Al-3Ce alloy shows the highest thermal conductivity of 122.2 W/m·K;The Mg-3.5Al-3Nd alloy shows the best fluidity.