通过DSC, OM, SEM, TEM观察及拉伸测试等手段对新开发的汽车用新型Al-0.93Mg-0.78Si-0.20Cu-0.30Mn-0.40Fe-3.00Zn (质量分数, %)合金的时效析出行为进行了系统研究. 结果表明, 固溶淬火态合金的DSC曲线出现5个放热峰, 分别对应GP区聚集长大及沉淀相析出, 运用Avrami-Johnson-Mehl方法对合金时效析出动力学进行了计算分析, 创建的沉淀相析出动力学方程Y=1-exp[-2.03×10¹⁹exp(-23573/T)t²]可以比较准确地预测合金时效析出规律. 185 ℃人工时效90 min即可达到峰值硬度133 HV, 对应的拉伸性能可达σ_0.2=346 MPa, σ_b=383 MPa, δ=13%, 拉伸断口仍以塑性断裂为主. 虽然该合金含有一定量的Zn, 但在185 ℃时效时仍以Mg-Si相的析出为主, 峰时效态分布有结构稳定的β′′相及其前驱体pre-β′′相, 后者的出现主要是由于Zn参与了沉淀相的析出所致. 此外, 根据合金时效过程的组织演化规律, 提出了该新型合金沉淀相形核和析出模型示意图.

To reduce the weight of car body, Al-Mg-Si-Cu 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. However, their bake hardening responses still need to be further improved to enhance their dent resistance. In this work, an advanced Al-0.93Mg-0.78Si-0.20Cu-0.30Mn-0.40Fe-3.00Zn (mass fraction, %) alloy has been developed, its precipitation behavior has been investigated systematically through DSC, OM, SEM, TEM and tensile test. Five exothermic peaks were observed in DSC curve of the solution quenched alloy, these peaks were believed to be caused by the formation of GP zones and precipitate phases, the formation and dissolution of these precipitates were analyzed by Avrami-Johnson-Mehl method, a kinetic equation Y=1-exp[-2.03×10¹⁹exp(-23573/T)t²] has been established, which can be greatly used to predict the precipitation behavior. After artificial aging at 185 ℃for 90 min, the peak hardness of 133 HV can be obtained, corresponding to the predicted results. Additionally, the tensile properties in peak aging state, i.e. yield strength, ultimate tensile strength and elongation, are 346 MPa, 383 MPa and 13%, respectively, and ductile fracture is the main fracture feature as observed by SEM examination of fracture surface. Although 3.00%Zn is added in the alloy, yet, Mg-Si precipitates are still the main precipitates formed during artificial aging at 185 ℃. Both β′′ and pre-β′′ precipitates can be observed in the peak aging state, and the presence of the latter ones should be resulted from the formation of Zn-containing clusters. In addition, based on the microstructure evolution of the alloy, a schematic diagram of forming precipitates in the Al-Mg-Si-Cu-Zn alloy is put forwarded.