双级淬火对车身板用6016铝合金烤漆硬化效应的影响Influence of interrupted quenching on paint-bake response of AA6016 Al alloy sheet

以硬度为主要表征手段研究双级淬火的中间淬火温度和保温时间对6016铝合金板材的时效及模拟烤漆行为的影响。采用DSC和透射电镜对比分析常规淬火和双级淬火对随后自然时效态样品与烤漆态样品纳米相的影响。结果表明：最佳的中间淬火工艺制度为(100 ℃, 1 h)，并且该工艺下合金自然时效过程性能稳定，但随后人工时效硬化速率大；双级淬火样品自然时效后表现出良好的塑性(δ＞28%)、成形性(σ_0.2＜120 MPa，n≈0.24，r≈0.78)和模拟烤漆后强化能力(σ_0.2＞220 MPa，PBR＞110 MPa)。双级淬火样品在100 ℃淬火时形成了均匀弥散并大于临界尺寸的Mg-Si团簇。这些团簇可抑制自然时效过程中小尺寸团簇的形成，从而保持这些样品的性能基本不变。这些团簇使得随后人工时效过程中β″相激活能由76.0 kJ/mol降至57.5kJ/mol，促进了模拟烤漆后形成的β″相的析出，从而提高双级淬火样品的烤漆硬化效果。

The influence of interrupted quenching temperature and holding time on the aging hardening behavior and paint-bake response of the AA6016 aluminum alloy was investigated with hardness test. The nano-size precipitates in the natural aged and paint-baked samples pre-processed by normal quenching or interrupted quenching were analyzed by DSC and TEM. The results show that the optimized interrupted quenching treatment is (100 ℃, 1 h). For the sample processed with this interrupted quenching, the hardness remains almost unchanged during natural aging, but the following artificial aging shows high hardening rate. The tensile test results also reveal that the interrupted quenching sample shows good ductility (δ＞28%), formability (σ_0.2＜120MPa, n≈0.24, r≈0.78) and paint bake hardening response (σ_0.2＞220 MPa，PBR＞110 MPa). The samples after interrupted quenching at 100 ℃ form many Mg-Si clusters that distribute homogeneously and have the size larger than critical size. These clusters suppress the formation of small clusters during natural aging, therefore, the properties of the samples remain almost unchanged. These clusters decrease the precipitation activation energy of β″ precipitates from 76.0 kJ/mol to 57.5 kJ/mol, which accelerates the precipitation of β″ precipitates, and increase the paint-bake hardening response of interrupted quenching samples.

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