挤压态6061铝合金动态力学性能及微观组织演变

摘要

采用分离式霍普金森压杆(SHPB),在应变速率为2000 s-1和5500 s-1条件下,对不同热处理状态下的6061铝合金挤压试样进行动态压缩实验.采用维氏硬度(HV)、 光学显微镜(OM)和透射电镜(TEM)对微观结构演变进行研究.实验结果表明:随着固溶温度增加,材料的动态力学性能不断增加,当固溶温度达到535℃达到稳定,此时基体中的二次相粒子基本溶解,同时未见发现晶粒尺寸明显长大现象.由于溶质原子溶入基体形成置换式固溶体,金属的晶体点阵发生畸变,固溶合金在高速冲击下,位错运动受到阻碍,位错密度增加,并形成位错墙.将535℃/1 h固溶后材料在180℃条件下进行人工时效,6061铝合金的动态流变应力随着时效时间增加而增加;当人工时效时间为8 h时,合金动态力学性能达峰值.时效初期形成了大量GP区,随着时效时间增加,GP区向β″转变,β″强化相的密度不断增加,并在8 h达到峰值.在高速冲击过程中,析出相有显著的钉扎作用,阻碍了位错的运动,导致大量的位错堆积,形成大量位错墙和位错胞.%The dynamic mechanical properties of extruded 6061 aluminum alloy under different heat treatment conditions were investigated by split Hopkinson pressure bar ( SHPB) . The compression strain rates were 2000 s-1 and 5500 s-1 . Vickers hardness, optical microscopy ( OM) and transmission electron microscopy ( TEM) have been used to study the microstructure evolution. The results showed that the dynamic stress of extruded 6061 aluminum alloy increased with in?creasing solution temperature until the temperature reaches 535 ℃. Most of the phases have dissolved in the matrix, and the grain size has no obvious change. During dynamic deformation, the motion of the dislocations was impeded due to the lattice distortion, and the dislocation walls were found. The solution treated 6061 aluminum alloy was aging treated at 180℃. The dynamic stress increases with aging time. The peak stress of the alloy was obtained when the aging time was 8 h. At the beginning of artificial aging, a number of GP zones are formed. As the aging time increasing, the GP zones trans?form to β″. The density of strengthening precipitation reached the peak when the aging time was 8 h. The pinning effect of the precipitation on the dislocation during dynamic deformation, resulted in the pile?up of dislocation, and formed a large number of dislocation walls and dislocation cells.