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本文利用金相显微镜(OM)、透射电子显微镜(TEM)及拉伸测试研究了不同Cu元素含量对Al-Mg-Si合金的析出行为和力学性能的影响，并结合差示扫描量热仪(DSC)对析出相的激活能进行定量计算，并通过硬度测试实验加以验证。结果表明，添加Cu元素可以促进β″相的析出，含Cu合金的析出相的数量密度更高且尺寸更细小。T4P态Base合金、 0.1%Cu-added合金及0.2%Cu-added合金的屈服强度差异较小，经过185℃×20 min的烤漆时效处理后，随着Al-Mg-Si合金中添加Cu含量的增加，合金的烤漆硬化能力得到提高，Base合金、 0.1%Cu-added合金及0.2%Cu-added合金的强度增量(∆Rp0.2)分别为87, 91和104 MPa。基于DSC分析计算出Base合金、 0.1%Cu-added合金及0.2%Cu-added合金在非等温时效过程中β″相的析出激活能(Q)分别为68.28, 63.48和55.42 kJ·mol-1，并建立了可预测合金中β″相析出速率的动力学方程；同时添加Cu元素可有效促进合金时效过程中β″相的形核率，致使合金的硬度更高，硬度增速更快。
Abstract：As the awareness of energy saving and emission reduction is gradually taking root in people's hearts, the trend towards automobile light weighting is inevitable. Aluminum alloys are extensively used as automotive lightweight materials due to their low density, high specific strength, good corrosion resistance, ease of processing and forming, and recyclability. Among these, 6 xxx series(Al-Mg-Si) aluminum alloys are particularly prevalent in the manufacture of automobile body panels due to their excellent properties such as medium-high strength and good formability. Al-Mg-Si alloys are heat-treatable and are reinforced alloys, and their main reinforcement mechanism is aging reinforcement, and β″ phase, which is the primary reinforcing phase within Al-Mg-Si alloys, is the sub-stabilized phase precipitated during the aging process. The precipitation behavior of Al-Mg-Si alloys can be modified by changing the composition or adjusting the heat treatment process, and Cu is frequently added to Al-Mg-Si alloys because the formation of a new precipitation phase, Q′, is observed during aging as well as the aging precipitation behavior of the alloys can be changed. Simulations indicate that the baking process for Al-Mg-Si alloy body panels should be conducted at 185 ℃ for 20 min, and this low-temperature, short-time treatment often fails to achieve the peak aging state of the alloy, and does not fully exploit the alloy's age-hardening potential of the alloy, leaving the alloy in an under-aged condition. There is a greater focus on the impact of Cu addition on the peak aging state of alloys, but fewer investigations have been conducted on the baking paint hardening behavior of Al-Mg-Si alloys in an under-aged condition with Cu addition. In summary, exploring the effect of Cu addition on the bake-hardening behavior of Al-Mg-Si alloy body sheets is of great significance. In this study, three alloy ingots with varying Cu contents—0, 0.1% and 0.2%—by introducing Cu into Al-0.6 Si-0.7 Si alloy and employing semi-continuous casting were produced. The ingots were then homogenized and processed through hot rolling, intermediate annealing, and cold rolling to achieve a 1 mm thick coldrolled sheet. The cold-rolled sheets were solution treated for 170 s at 555 ℃ in a salt bath furnace, followed by water quenching and a preageing treatment at 75 ℃ for 7 h to obtain T4P state alloy sheets. Subsequently, these T4P plates were subjected to an aging treatment at 185 ℃ for 20 min after pre-stretching by 2% to obtain T6B state plates. The microstructure and precipitation kinetic parameters of the alloy plates with different Cu contents were investigated using optical microscopy(OM), transmission electron microscopy(TEM) and differential scanning calorimetry(DSC). Mechanical property tests were conducted on an AG-XPlus 100 KN microcomputer-controlled electronic universal mechanical tester. Tensile specimens were cut from the cold-rolled plates perpendicular to the rolling direction to measure the yield strength of the alloy plates in both T4P and T6B states, determine the strength increment, and examine the impact of different Cu contents on the baking hardening behavior of the alloy. The microstructure analysis revealed that the grain structure of T4P state alloy was completely recrystallized, consisting of numerous equiaxed recrystallized grains. Despite some variations in the average grain size among the three alloys, the differences were minor and did not significantly affect strength. TEM results indicated that the precipitated phase in T6B state alloy remained β″ phase or Guinier-Preston(GP) region, but Cu-containing alloys exhibited higher precipitate density and finer particle size. The addition of Cu promoted the formation of β″ phase. Tensile test results showed that tensile strength increases with Cu content in the T4P alloy, while elongation remained unchanged. The yield strengths of T4P Base alloy, 0.1%Cu-added alloy and 0.2%Cu-added alloy were 93, 97 and 96 MPa, respectively. After a baking aging treatment at 185 ℃ for 20 min, the yield strengths increased to 180, 188 and 200 MPa, with strength increments (∆Rp0.2) of 87, 91 and 104 MPa, respectively, demonstrated that the baking hardening capacity of Al-Mg-Si alloys was enhanced with increasing Cu content. The activation energies(Q) for β″ phase precipitation during non-isothermal aging were calculated from DSC curves for Base alloy, 0.1%Cu-added alloy and 0.2%Cu-added alloy as 68.28, 63.48 and 55.42 kJ·mol-1, respectively. Kinetic equations predicting the precipitation rates for Base alloy, 0.1%Cu-added alloy and 0.2%Cu-added alloy were derived based on Q and kinetic parameters(k0, Tpeak, t) from the calculations: Y=1-exp[-4.45×1012t2 exp(-16426/T)], Y=1-exp[-5.76×1011t2 exp(-15270/T)], Y=1-exp[-1.51×1010t2 exp(-13332/T)]. Furthermore, the addition of 0.2%Cu significantly promoted the nucleation rate of β″ phase during aging, leading to increased hardness and a more rapid hardness increase within the first 20 min of aging at 185 ℃. The hardness of 0.2%Cu-added alloy increased from HV 70.9 to HV 100.3 (∆HV=HV 29.4) compared to Base alloy, which increased from HV 68.4 to HV 86.5 (∆HV=HV 18.1).
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基本信息:
DOI：10.13373/j.cnki.cjrm.XY24020008
中图分类号:TG146.21
引用信息:
[1]程大航,刘贞山,陈凯欣,等.微量Cu对Al-Mg-Si合金烤漆硬化行为及力学性能的影响[J].稀有金属,2026,50(02):159-168.DOI:10.13373/j.cnki.cjrm.XY24020008.
基金信息:
国家重点研发计划项目(2021YFB3704203,2023YFB3710401)资助
2026-02-15
2026-02-15