Mg-8Zn-4Al-0.5Cu-0.5Mn-xLi高模量铸造镁合金的组织和性能

Microstructure and Properties of As-cast Mg-8Zn-4Al-0.5Cu-0.5Mn-xLi Alloys with High Modulus

设计和制备Mg-8Zn-4Al-0.5Cu-0.5Mn-x Li(x=0,3,5,7)(%,质量分数)系列高比模量的镁合金,研究了它的组织和性能。Li含量为3.14%和5.37%的两种镁合金,其基体为单相α-Mg,在晶界析出骨骼状Mg_(32)(Al,Zn)49相,在晶粒内有颗粒状Mg_(5)Al_(2)Zn_(2)相和Al_(2)Mn相;Li含量为7.57%的合金,其基体主要为双相组织α-Mg+β-Li。添加Li元素后在晶界附近生成的共晶组织由α-Mg相和层片状AlLi相组成,并随着Li含量的提高层片状AlLi相的含量随之提高。随着Li含量的提高,合金的屈服强度呈逐渐提高的趋势,而抗拉强度基本上不变,合金的弹性模量呈现先提高后降低的趋势。铸态合金ZA84-5Li的弹性模量可达51.89 GPa,比纯Mg的弹性模量高7 GPa,但是其力学性能基本不变,屈服强度为141 MPa,抗拉强度为189 MPa,密度为1.71 g/cm^(3)。

Aiming at the demand of high stiffness light metal structure materials,high specific modulus Mg-alloys Mg-8Zn-4Al-0.5Cu-0.5Mn-xLi(x=0,3,5,7)(%,mass fraction)(namely ZA84-xLi)were designed 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-phaseα-Mg,while the skeletal-like Mg_(32)(Al,Zn)49 phase is precipitated near grain boundaries,and there is a granular-like Mg_(5)Al_(2)Zn_(2)phase and Al_(2)Mn phase inside the grain;when the Li content is 7.57%,the alloy matrix is mainly a dual-phase structureα-Mg+β-Li.After the addition of Li,many eutectic structures are formed near the grain boundaries,which are composed ofα-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/cm^(3)respectively for the cast alloy.