材料期刊网

针对铝合金焊缝性能低于母材、现有成形极限分析方法不适宜分析铝合金搅拌摩擦焊板材成形极限的现状,提出了一种基于二次多项式新本构模型的铝合金拼焊板成形极限理论模型。核心思想为利用材料自身的性能差异替代经典M-K理论模型的沟槽假设。针对铝合金硬化指数低、幂指数回归精度差的问题,将二次多项式新本构模型应用于M-K理论模型,最终建立了适合于铝合金搅拌摩擦焊拼焊板的成形极限理论预测模型。对铝合金搅拌摩擦焊板材进行了成形极限实验,并通过XJTUDIC三维数字散斑应变变形测量系统实时测量变形过程中的应变值,得到了铝合金搅拌摩擦焊拼焊板的实验成形极限图。最后对实验结果和理论分析结果进行了对比。相比传统的幂指数本构模型,二次多项式对应力-应变曲线的回归,无论在初试屈服阶段或后期变形阶段均有很好的吻合精度。幂指数最大拟合误差超过12%,而二次多项式的拟合误差小于1%,二次多项式回归模型能很好地拟合铝合金搅拌摩擦焊接接头的应力-应变关系;采用二次多项式本构关系的理论模型能很好地预测铝合金搅拌摩擦焊板材的成形极限,第一主应变的预测误差小于0.01;而幂指数理论模型则导致平面应变状态下的极限应变预测结果明显不准,在相同应变路径下第一主应变的预测误差达0.14。

Automobile lightweight can effectively save fuel consumption and reduce CO₂ emissions. Aluminum and its alloys are desirable for the automotive industry due to their excellent high-strength to weight ratio. However, due to the introduction of the welding seam, it has brought new changes to the forming process, especially to the forming limit. To establish a reasonable forming limit curve (FLC) analysis method of friction stir welding (FSW) aluminum alloy blank, a new theoretical model was proposed based on the new second order function constitutive model. The main idea is using the differences in mechanical property between the welding and heat affected zone substitution for the hypothesis of geometry groove in the classic M-K theoretical model. The new second order function constitutive model was applied to M-K theoretical model. Eventually, a new FLC theoretical model for FSW aluminum alloy blank was established. Such theoretical model also overcomes the low strain hardening exponent of aluminum alloy material, which leads to a poor regression accuracy by power-exponent function model. The forming limit test for FSW aluminum alloy blank was performed, and the real-time strain was measured by three-dimensional digital speckle strain measurement system (XJTUDIC). Finally, the results of experiments and the theoretical analysis are compared. Compared with the traditional power law, the regression result of the new second order function constitutive model on the stress-strain curve no matter in the initial yield stage or in late deformation stage has a good fitting precision. The maximum fitting error of the power law on the stress-strain curve is more than 12%, but the fitting error of the new second order function constitutive model is less than 1%. The theoretical prediction based on the new second order function constitutive model is significantly better than the theoretical predictions based on power law in predicting the forming limit of FSW aluminum alloy blank. The prediction error of the first principal strain based on the new second order function constitutive model is less than 0.01. While the maximum prediction error of the first principal strain based on the power law is 0.14.