新型Al-Mg-Si-Cu-Zn合金板材組織、織構和性能的優化調控

新型Al-Mg-Si-Cu-Zn合金板材組織、織構和性能的優化調控OPTIMIZATION AND CONTROLLING ON THE MICROSTRUCTURE, TEXTURE AND PROPERTIES OF AN ADVANCED Al-Mg-Si-Cu-Zn ALLOY SHEET

通過OM、SEM，TEM觀察以及EBSD和力學性能測試等手段研究了不同熱加工工藝對Al-Mg-Si-Cu-Zn合金板材組織、織構和成形性能，以及固溶淬火后等溫時效對其析出行為的影響規律。結果表明，兩種熱加工工藝對T4P預時效態合金的強度和應變硬化指數n基本無影響，但是對?r、Δr以及不同方向延伸率影響顯著；不同熱加工過程對合金組織和織構演化均有影響，成形性能較好的固溶淬火態合金板材平均晶粒尺寸略大且呈雙模型晶粒尺寸分布特征，其織構組分較多，但是強度較低。對該淬火態合金進行185 ℃人工時效20min，其硬度即可升高65HV，進一步時效到5h達到峰值硬度132HV，對應的拉伸性能可達σ0.2=318 MPa，σb=364 MPa，δ=13%，拉伸斷口為典型的塑性斷裂。該合金在185 ℃時效時仍以Mg-Si相析出為主，如?"、?’和Q’相等，峰時效后?"主要沿b軸方向生長最后轉化為?’和Q’相，合金表現出較好的時效穩定性。

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 aging 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 study, both the effect of different thermomechanical processes on formability, microstructure and texture of Al-Mg-Si-Cu-Zn alloy, and the influence of aging 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 possessing a better formability after the T4P treatment. The hardness increment of 65HV can be achieved in the quenched alloy after artificial aging treatment of 185 ℃/20min. And then the peak-aging state can be obtained after aging 5hs, the hardness and tensile properties, i.e. yield strength, ultimate tensile strength and elongation, are as follows, 132HV, 318MPa, 364MPa and 13%, respectively, and ductile fracture is the main fracture feature as observed by SEM examination of fracture surface. Mg-Si precipitates, such as ?"、?’ and Q’ phases, are still the main precipitates formed after artificial aging at 185℃, and ?" phases mainly grow along its b axis and finally transform into ?’ and Q’ phases, which is the main reason for the observed better aging stability during long time artificial aging treatment.

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