淬火速率对含Sc(Zr)高强韧Al-Zn-Mg-Cu合金微观组织和力学性能的影响

通过末端淬火实验(JEQ)、X射线衍射仪(XRD)、扫描电镜(SEM)、透射电子显微镜(TEM)研究一种热挤压Al-Zn-Mg-Cu-Sc-Zr棒材的淬火敏感性。结果表明:随着距离淬火端越远,冷却速率从1800℃/min下降至111℃/min,合金硬度从150 HB下降至133 HB,抗拉强度从430 MPa下降至375 MPa。当冷却速率为131.2℃/min时,合金的硬度为135 HB,合金淬透深度约为93mm。随着冷却速率的降低,端淬时远离淬火端位置,平衡η相先后在晶界、晶内处析出、长大、粗化;时效后,析出的η′强化相的数量减小;时效后,合金内出现无沉淀析出带(PFZ),晶界的PFZ变宽,宽化至160 nm。

Effects of quench rate on mechanical properties and microstructures of high strength and toughness Al-Zn-Mg-Cu alloy with Sc(Zr)addition

The quench sensitivity of the Al-7.01Zn-1.39Mg-2.25Cu-0.07Zr-0.07Sc alloy were investigated by the Jominy end-quench(JEQ)test,X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that,with the increase of the distance from the quenched end of the bar(d)and the decrease of average cooling rates from 1800℃/min to 111℃/min,the hardness falls to 133 HB from 150 HB and the tensile strength falls to 375 MPa from 430 MPa.When the critical average cooling rate is about 131.2℃/min and the d is 93 mm,90%of the maximum hardness can be obtained.As the cooling rate reduces,the microstructure change as follows:theηequilibrium phase forms in the grain boundary and grained at different positions from the quenching end in the JEQ process in sequence,the number ofη′strengthening precipitates decreases after aging,the width of precipitate free zone near grain boundaries reaches up to 160 nm.