Study On Formability Of 6000 Series Aluminum Alloy Sheet For Auto-body

The demands for automobile lightening have led to increasing interest in aluminum sheets for auto-body applications so as to reduce vehicle emissions. Many studies have shown that alloy composition, rolling and heat-treating processes have significant influence on the fomability of 6000 series aluminum alloy. The improvement in formability is one of the most important key factors to expand the applicability of aluminum alloy sheets to various types of structural members.Four Al-Mg-Si-Cu alloys with different alloy compositions and four different rolling processes were designed to investigate the correlation between microstructure and formability in this study. The microstructure and texture were characterized by optical microscopy(OM), X-ray diffraction(XRD) and electron back scattering diffraction(EBSD) techniques. Tensile tests and Forming Limit Diagram(FLD) were used to characterize the formability of tested alloys. The main results are shown as below:(1) The strength and elongation of Si-rich alloys are higher than Mg-rich alloy, and the strength of high Cu alloys are better than low Cu alloys. N value of four alloys have little difference, r value of Mg-rich high Cu alloy is relatively higher than the other three.(2) The texture of hot-rolled sample is composed of Copper, S, Brass and R. After the primary rolling and intermediate annealing, the structure is recrystallized, and recrystallized grain size decreases with the rolling reduction. Then the Si-rich sheets with high Cu are finally rolled to 1mm, with increasing of rolling reduction, the elongated structure is more obvious, the remaining Cube and Cube+ND20 textures gradually decrease, and Copper, S, Brass textures significantly increase. After continuous annealing and pre-aging, the rolling textures turn into recrystallization textures, and with increasing rolling reduction, R and Brass-R components significantly decrease, but Cube and Cube+ND20 components increase evidently, indicating that PSN and the Cube band nucleation dominate the recrystallization mechanism with increasing rolling reduction. And recrystallized grain size decreases with the rolling reduction. The sheet made by 3th process has low yield strength, high tensile strength and good elongation, which is appropriate for forming processing.(3) The formability of 6016 aluminum alloy is tested after being stored for 4 and 6 months. Results from testing organization I show good aging resistance.