The Influence Of Alloying Elements And Heat Treatment Of Al-mg-si-based Automotive Body Sheet Organization And Performance

At present, vehicles are developing to be lightweight, high speed, safety, comfort, energy-saving and environmental protecting. It is a trend to increase the aluminumzation of vehicles. Among all aluminum alloys for automotive body sheets,6xxx alloys have been used widely because of its good combinational properties of high strengths excellent formability, good corrosion resistence.In this paper, the influences of alloy compositions and heat treatment on the microstructure formability and tensile properties are investigated by lots of analysing and testing methods such as microscope , Transmission Electron Microscope(TEM), X-ray Energy-Dispersive Spectrocopy (EDS), Scanning Electron Microscope (SEM), Differential Scanning Calorimeter(DSC), Electron Microprobe Analyser, microhardness measurement, tensile testing, X-Ray Diffraction etc. The alloy compositions and heat treatment are optimized.The results of the study show that:1.The effect of Cu, Mg, Si, Zr on the tensile strength of T6 temple is Si>Cu.>Mg>Zr; Zr has a significant influence on the Cu plays a important role in influencing anisotropic plastic parameter(r) and Cu, Mg, Si, Zr have little influence on the strain-hardening exponent(n).2. A Small volume fraction of Zr in Al-Mg-Si based alloys will precipitate (Al3Zr) dispersoid phase, which can inhibit recrystallization, as well as provide substructure strengthening and dispersoid strengthening. The properties of Al-Mg-Si based alloy containing 0.2wt.% Zr are improved.3. With the increase of solution treatment temperature, the content of Si in a(Al) solution solid increased, while the content of Mg in a(Al) solution solid changed little. The increasing solution treatment temperature resulted in the increase of strength and hardness of artificial aging.4.During natural aging, the precipitates are mainly G.P. Zone. .' (Mg2Si) phase is the mainly strengthening phase during artificial aging. A delay at room temperature betweenquenching and artificial aging could decrease the hardness of the alloy during artificial aging, the longer the delay, the lower the hardness, while proper pre-aging temperature and excess Si could alleviate the detrimental effect of natural aging.5.The optimum alloy composition is Al-0.95Mg-l.35Si-l.2Cu-0.2Zr-0.01Ti. The ideal heat treatment parameters are 550 +30min solution 150 +5min pre-aging175+5h artificial aging.6. The of the optimized alloy is smaller than American AA6010 by 20%, strain-hardening exponent(n) of the optimized alloy is the same as American AA6010, anisotropic plastic parameter(r) of the optimized alloy is higher than American AA6010 by 4.3%, tensile elongation of the optimized alloy is higher than American AA6010 by 8.3%, So the optimized alloy has better formability than American AA6010 in T4 temple. In T6 temple, this alloy has better mechanical properties than traditional auto body sheets except a lower tensile elongation.The results provide an effective way to design ideal Aluminum alloys with excellent properties for automotive body sheets, and it would play a positive role in solving the difficult problem of automotive body sheets depending on importing and making automotive industry of our country develop rapidly.