采用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)和差示扫描量热仪(DSC)等分析手段研究了A1-7.0Zn-2.9Mg合金板在制备过程中及不同时效热处理工艺下的显微组织及力学性能.结果表明,A1-7.0Zn-2.9Mg合金铸态组织主要由α(A1)+ Mg32(Al,Zn)a9 (T)相共晶组织、A1(Fe,Mn) Si相和少量过剩T相组成.经均匀化处理后,共晶相基本溶入基体中,基体中又重新析出MgZn2粒子及少量Al3Zr相.热轧后的晶粒组织沿轧制方向呈纤维状分布.试验了一种低温时效+常规时效的LTA工艺,结果显示,LTA态的合金强度和伸长率均略高于峰值时效(T6)和回归再时效(RRA)态.同时,析出相尺寸明显大于T6、RRA和双极时效(T73)态,且晶界析出相呈粗大不连续分布,具有较好的抗应力腐蚀开裂(SCC)潜力.
Microstructure and mechanical properties of A1-7.0Zn-2.9Mg alloy sheets during preparation and after different aging processes were investigated by means of optical microscope (OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction (XRD),differential scanning calorimetry (DSC).The results show that the as-cast A1-7.0Zn-2.9Mg alloy consists of α (A1) + Mg32 (A1,Zn) 49 (T) phase eutectic structure,Al(Fe,Mn) Si phase and a few excess T phases.After homogenization,the eutectic phase is dissolved into the α(Al) matrix,meanwhile,fine MgZn2 particles and A13Zr phase precipitate in the α(A1) matrix.Grain structure of the alloy exhibits as fibrous structure along the rolling direction after hot roiling.A Low temperature preaging + conventional aging treatment (termed LTA) was employed as artificial aging for the alloy.The results show that the strength and elongation of the A1-7.0Zn-2.9Mg alloy under LTA temper are slightly higher than that of with T6 temper and RRA temper.Meanwhile,the size of precipitates in the Al-7.0Zn-2.9Mg alloy under LTA temper is larger than that of with T6 temper,RRA temper or T73 temper.Good stress corrosion cracking (SCC) resistance of the alloy under LTA temper can be expected because of the larger size and spacing of the grain boundary precipitates.
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