Microstructure and Properties of As-cast Mg-8Zn-4Al-0.5Cu-0.5Mn-xLi Alloys with High Modulus
Aiming at the demand of high stiffness light metal structure materials,high specific modu-lus Mg-alloys Mg-8Zn-4Al-0.5Cu-0.5Mn-xLi(x=0,3,5,7)(％,mass fraction)(namely ZA84-xLi)were de-signed and prepared,as well as and then optimized.When the Li content in the alloy is 3.14％and 5.37％,the alloy matrix is composed mainly of single-phase α-Mg,while the skeletal-like Mg32(Al,Zn)49 phase is precipitated near grain boundaries,and there is a granular-like Mg5Al2Zn2 phase and Al2Mn phase inside the grain;when the Li content is 7.57％,the alloy matrix is mainly a dual-phase structure α-Mg+β-Li.After the addition of Li,many eutectic structures are formed near the grain boundaries,which are composed of α-Mg phase and lamellar-like AlLi phase,and with the increase of Li content,the amount of lamellar-like AlLi phase also gradually increases.The yield strength of the alloy increases gradually with the increase of Li content,while the tensile strength remains basically unchanged.The elastic modulus of the alloy increases first and then decreases with the increase of Li content.For the as-cast ZA84-5Li,the elastic modulus can reach 51.89 GPa,which is 7 GPa higher than that of pure Mg,while the mechanical properties of the alloy basically keeps unchanged.Namely,the yield strength,tensile strength and density is 141 MPa,189 MPa and 1.71 g/cm3 respectively for the cast alloy.
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