# 材料期刊网

To reduce the weight of car body, Al-Mg-Si-Cu series alloys have been widely used to produce outer body panels of automobiles due to their favorable high-strength-to-weight ratio, corrosion resistance and good formability. Moreover, the strength of Al-Mg-Si-Cu series alloys can be enhanced by artificial ageing treatments. However, their formability and final strengths still need to be further improved compared to steels, which are the major obstacles to wide-scale application of aluminum in the automotive fields. In this work, both the effect of different thermomechanical processes on formability, microstructure and texture of Al-Mg-Si-Cu-Zn alloy, and the influence of ageing treatment on its precipitation behavior were studied through mechanical property tests, OM, SEM, TEM and EBSD measurements. The results reveal that both the strengths and strain-hardening component n value of the T4P treated alloys are not affected by the two thermomechanical processes, but the $r?$, Δr and elongations in the different directions are significantly affected. The microstructure and texture evolution of the alloy in the two thermomechanical processes are different from each other. Both the microstructure of a little coarser and bi-modal grain size distribution, and the texture characteristics of much more components but with quite lower intensities can be seen in the solution treated alloy sheet which possesses a better formability after the T4P treatment. The hardness increment of 65 HV can be achieved in the quenched alloy after artificial ageing treatment of 185 ℃, 20 min. And then the peak-ageing state can be obtained after ageing 5 h, the hardness, yield strength, ultimate tensile strength and elongation, are as follows, 132 HV, 318 MPa, 364 MPa and 13%, respectively, and ductile fracture is the main fracture feature as observed by SEM examination of fracture surface. Mg-Si precipitates, such as β", β' and Q' phases, are still the main precipitates formed after artificial aging at 185 ℃, and β" phases mainly grow along its b axis and finally transform into β' and Q' phases, which is the main reason for the observed better ageing stability during long time artificial ageing treatment.

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