Study of the aging precipitation and hardening behavior of 6005A alloy sheet for rail traffic vehicle

The single-stage aging process, microstructure evolution during the precipitation process and crystal structure and orientation relationships between the β″ phase and matrix were studied by means of conventional transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and hardness testing in 6005A aluminum alloy used for rail traffic vehicle. The results show that 6005A alloy can reach its peak hardness after aging at 175 for 12 h, and maintain it for a longer time. It is found that there exist clusters or GP zones in this alloy at early stage of aging and the β″ phase at the peak-aging stage. After the peak-aging, the β″ phase as a main strengthening phase in 6005A aluminum alloy continues being precipitated from matrix for a long time. β″ phase has a C-centered monoclinic lattice with the lattice parameters a=(1.52±0.04) nm, b=0.405 nm, c=(0.67±0.04) nm, β=105.26°. The crystallographic orientation relationship between the β″ phase and matrix is found as follows: (010)_β″//(001)_Al, [200]_β″//[230]_Al, [002]_β″//[3̄10]_Al. And, the precipitation sequence with aging time in 6005A aluminum alloy can be described: super-saturated solid solution (SSS) → clusters → GP zone → metastable β″ phase → metastable β′ phase+Q′ phase → stable β (Mg₂Si) phase+Q phase.