T4和T6热处理参数对Mg-12Zn-2Al镁合金组织和性能的影响

Effects of T4 and T6 heat treatment parameters on microstructure and mechanical properties of Mg-12Zn-2Al magnesium alloy

通过在Mg-12Zn合金中添加2%Al(质量分数)制备出一种新型Mg-12Zn-2Al(ZA122)镁合金,并利用光镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)和力学性能测试研究ZA122合金在铸态、T4和T6处理后显微组织和力学性能的变化规律。结果表明:铸态组织主要由α-Mg基体和共晶相(α-Mg+Mg2Zn3+Mg7Zn3+Mg32(Al,Zn)49)组成。合金经330℃固溶32 h后获得较均匀的组织和231 MPa抗拉强度及9.23%的伸长率。合金双级时效的强化效果优于单级时效的,且提前24 h获得力学性能峰值。经过(180℃,48 h)单级时效后,抗拉强度和伸长率的峰值分别为283 MPa和8.03%;采用(90℃,24 h)+(180℃,24 h)双级时效后,同时出现了抗拉强度和伸长率的峰值为294 MPa和7.81%。单级时效下,合金中沉淀相的形核机制主要借助于位错、空位、层错、亚晶界和晶界等晶体缺陷实现异质形核。双级时效下,预时效时脱溶析出的G.P.区或团簇原子作为亚稳相和平衡相的现成异质形核核心实现异质形核。

A new type Mg-12Zn-2Al magnesium alloy(ZA122)was fabricated by adding 2%Al(mass fraction)in Mg-12Zn alloy,and the microstructure and mechanical properties of the alloy under the conditions of as-cast,solution and aging treatment were investigated with an OM,SEM,TEM,XRD and mechanical tests,respectively.The results show that the as-cast microstructures are mainly comprised ofα-Mg matrix,eutectic phases(α-Mg+Mg2Zn3+Mg7Zn3+Mg32(Al,Zn)49).After being solutionized at 330℃for 32 h,the alloy reveals relatively homogeneous microstructure and perfectly mechanical performance with an ultimate tensile strength(UTS)of 231 MPa and an elongation(EL)of 9.23%,respectively.The effect of two-step strengthening is better than that of single-aging strengthening of the alloy,and the peak mechanical properties are obtained 24 h in advance.After single-aged by(180℃,48 h),the peak values of UTS and EL are 283 MPa and 8.03%,respectively.While the maximum values of UTS 294 MPa and EL 7.81%are simultaneously achieved from the alloy experienced two-step aging(90℃,24 h)+(180℃,24 h).During single-aging process,the nucleation mechanism of precipitated phases of the alloy is mainly realized by dislocation,vacancy,stacking fault,sub-grain boundary,grain boundary and other crystal defects.In the course of two-stage aging,the generated G.P.zones or clustered atoms during the pre-aging process play ready-made heterogeneous nucleation role in the from process of metastable and equilibrium phases.