Effect of 90% cold rolling on precipitation behavior of Al-0.6Mg-1.0Si-0.5Cu alloy

Since 6000 series aluminum alloys have high hardness based on precipitation strengthening and good corrosion resistance, they are utilized as automobile body sheet panels in the industry. In order to reduce the weight of automobiles, further improvement of hardness is required. To improve the hardness, the process of severe plastic deformation before artificial aging (T8 treatment) was suggested. However, the effect of severe plastic deformation on the precipitation behavior of the alloys is not clear. In this study, 90% cold rolling was conducted for an Al-0.6Mg-1.0Si-0.5Cu alloy as the thermo-mechanical treatment. It was compared that precipitation behavior between T6 and T8 treated alloys by Micro Vickers hardness test, electrical conductivity measurement, differential scanning calorimetry and transmission electron microscopy. As the results, in T8 treated alloys, both precipitation strengthening and recovery softening happened during aging. However, the peak hardness of T8 treatment was larger than that of T6 treatment. The precipitation process was accelerated by lattice defects such as vacancies and dislocations introduced during 90% cold rolling. The precipitations in T8 treatment aged for 10.8 ks were identified as β”, β' and Q'. It was confirmed that β'(Q') phases precipitated directly along dislocations in 90% cold-rolled alloys.