Effect of pre-aging on microstructure and properties of 2000 series aluminum alloy for automotive body sheets

摘要

The effect of pre-aging treatment on the tensile properties, formability and microstructures of 2036 aluminum alloy for automobile body sheets were investigated through the tensile tests, DSC analysis and TEM observation. The results show that the alloy was softened, which was pre-aged at 180°C within 20min and then natural aging, namely T4P. However, the yield strength decreases first and then rises. The yield strength of the alloy after T4P (10min) reach the minimal 202.3MPa, but the elongation and strain hardening exponent arrive at the maximum, 25.5% and 0.26 respectively, which can improve its formability effectively. In the early stage of T4P, GP zones dissolve, and generate some θ" nuclei, so that the strengthening effect is restrained during the natural aging following the pre-aging. With the increment of pre-aging time, the θ" phases are formed. The number of the θ" phases grows, and the strength increases sharply during the paint-bake treatment. In contrast with the 6000 series aluminum alloy for automobile body sheets, the paint-bake hardenability of the 2036 alloy is lower and its yield strength before the paint bake is accordingly higher, which will add the difficulty of forming for the sheet.