Ca对Mg-5Al-8Zn-xCa镁合金显微组织与力学性能的影响

采用重力铸造法制备了Mg-5Al-8Zn-x Ca(x=0,1.75,2.0,2.25,2.5,2.75,3.0,wt%)合金。使用XRD、OM和SEM等研究了Ca含量对合金组织与力学性能的影响。结果表明:铸态Mg-5Al-8Zn-x Ca合金主要由α-Mg基体、β-Mg17Al12相、Mg32(Al,Zn)49相及MgZn2相和Al2Ca相组成。当Ca含量从1.75wt%增加到2.75wt%时,基体晶粒显著细化,β-Mg17Al12相由粗大的连续网状转变为细小的断续网状分布于晶界上,层片状Al2Ca相也显著细化,此时合金的拉伸强度达到最大值138 MPa,较未加Ca时提高了27.8%;Ca含量继续增加至3.0wt%,晶粒又发生粗化,合金拉伸强度发生下降;拉伸断裂形式均为准解理脆性断裂。

Effects of Ca content on microstructures and mechanical properties of Mg-5Al-8Zn-xCa magnesium alloys

Mg-5Al-8Zn-xCa( x= 0, 1.75, 2.0, 2.25, 2.5, 2.75 and 3.0 wt%) Mg alloys were prepared by gravity casting. The effects of Ca content on microstructures and mechanical properties of the alloys were investigated by XRD, OM and SEM. The results show that the as-cast Mg-5Al-8Zn-xCa alloy is composed mainly of a-Mg matrix, b-Mg17Al12, Mg32(Al, Zn)49, MgZn2 and Al2Ca phases. With the increase of Ca content from 1.75% to 2.75%, the matrix grain is obvious refinement, the morphological change in b-Mg17Al12 phase occurs from coarse continuous network to fine intermittent network and distributed on the grain boundaries, the lamella-type phase Al2Ca is obvious refinement too, meanwhile the tensile strength of the alloy at room temperature reaches maximum, it is 138 MPa, increased by 27.8%, compared with the alloy with absence of Ca addition. When the Ca content reaches 3.0%, the grain is coarsened once more, meanwhile the tensile strength of the alloy decreased. The tensile fractures of the alloys are characterized by quasi-cleavage at room temperature.