Study On Mechanical Properties And Microstructure Of 6061 Aluminum Alloy During Hot Deformation And Aging

6061 aluminum alloy is one of the Al-Mg-Si system alloy that can be significantly hardened by a proper heat treatment. Due to its good mechanical properties, higher corrosion resistance, better weld ability and lower cost compared to other aluminum alloys, it has broad applications in automobile parts and substitutes for steel. Over the past decades, the 6061 aluminum alloy has been used in the automotive industry for the fabrication of several types of automotive parts, such as wheel, panels, and even in the vehicle structure. Automotive bumper plays an important part in absorbing energy in crashing at low speed as buffer. In this paper, the tensile mechanical properties, micro structure evolution of 6061 aluminum alloy which was manufactured for bumper were investigated.The homogenization is an important heat treatment step for wrought aluminum alloy products. The influence of homogenizing treatment temperature and holding time on the structure and performance of 6061 aluminum alloy were investigated by hardness analysis and electronic microscopy analysis (SEM, TEM). Meanwhile, the diffusion kinetics of the elements during the homogenizing treatment was studied. The homogenizing equation was deduced. The results showed that the reasonable homogenizing regulation of 6061 alloy was the annealing at 550℃for 12h.Hot compression tests of 6061 aluminum alloy after homogenization at 550℃/12h were performed on Gleeble-1500 at deformation temperatures ranged between 350℃～500℃and strain rates ranged between 0.001～10s-1. The varieties of flow stress was described by the Zener-Hollomon parameter Z in the hyperbolic sine equation. The microstructures of 6061 aluminum alloy during deformation were observed by optical microscope. Softening mechanisms and the relationships between the parameters of deformation were discussed. The results showed that dynamic recovery was the dominative restoring mechanism during the hot compression during the various deformation conditions. The deformation conditions dramatically affected the ongoing heat treatment microstructures of 6061 aluminum alloy.On the time of crashing, the easier the bumper can deform, the more energy can be absorbed. The best strength could be gained when T6 treatment was held in 6061 aluminum alloy, but at this condition, elongation was much lower. The low elongation limited the absorption of energy when crash happened. Effects of natural aging on micro structure and mechanical properties of the 6061 aluminum alloy used for bumper with the shape of"目"were investigated by tensile test, transmission electron microscopy. The results showed that the mechanical properties of the aluminum alloy reached steady in about a month, the alloy had high elongation which could meet the demands of bumper. Based on the treatment, Bar-bar tensile impact testing apparatus was used to study mechanical behavior of 6061 aluminum alloy at different strain rates. The results of this experimental were used to define a new set of material constants for the strength component of the Johnson-Cook model for 6061 alloy.