The formability of friction stir welded (FSW) AA7075-O aluminum alloy sheet specimens was tested under a range of warm uniaxial and biaxial loading conditions. To study the effect of FSW process conditions on formability, four groups of specimens were prepared using a range of FSW parameters. Two rotational speeds (500 and 1000 rpm), four travel speeds (4.2, 5.1, 8.5, 12.7 mm/s), and four axial force levels (6895, 7006, 7117, 7346 N) were included in the test matrix. Each specimen had a butt joint centrally located and oriented parallel to the sheet rolling direction. Specimens from each of the four groups were then tested under different combinations of uniaxial (e.g., transverse tensile test) and biaxial loading conditions (bulge test), including at two different strain rates (0.0013 and 0.013 1/s) and three different temperature levels (25, 200, and 300 °C). From the flow curves obtained from each test combination, the relative effect that FSW parameters (rotational speed, travel speed, and axial force) and forming parameters (temperature and strain rate) had on formability was investigated in detail. Mechanical and structural variations of the weld zone were compared with those of the base material. Tool rotational speed was observed to have a major effect on the yield and tensile strength of FSW blanks, with strengths varying by as much as 20% over the range process and forming parameters tested. Stress-strain curves obtained by using hydraulic bulge tests yielded a 5–10% increase in strain values compared with uniaxial tensile test results. In the bulge tests, the fracture zone was only observed to occur at the apex of the dome along the joint line for specimens tested at 300 °C and a strain rate of 0.0013 1/s. Specimens tested under other FSW parameters and process combinations did not fail in this location. In tensile tests, the specimens were only fractured on the welding line under forming conditions of 300 °C and at either the low or the high strain rate. Otherwise, the specimens failed away from the joint line. The maximum dome height, as a measure of formability, was obtained under forming conditions of 200 °C temperature and at a 0.0013 1/s strain rate. This result correlated well with stress-strain curves obtained from uniaxial tension testing.

中文翻译：

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AA7075-O摩擦搅拌焊接接头的单轴和双轴变形特性

搅拌摩擦焊接（FSW）AA7075-O铝合金薄板样品的可成形性在一定的单轴和双轴热加载条件下进行了测试。为了研究FSW工艺条件对可成形性的影响，使用一系列FSW参数制备了四组样品。测试矩阵中包括两个转速（500和1000 rpm），四个行进速度（4.2、5.1、8.5、12.7 mm / s）和四个轴向力水平（6895、7006、7117和7346 N）。每个试样的对接接头位于中心并平行于薄板轧制方向定向。然后，在单轴（例如，横向拉伸试验）和双轴载荷条件（膨胀试验）的不同组合下测试了四组样品，包括两种不同的应变率（0.0013和0.013 1 / s）和三种不同的温度水平（25，200，和300°C）。从每种测试组合获得的流动曲线中，详细研究了FSW参数（转速，行进速度和轴向力）和成形参数（温度和应变率）对成形性的相对影响。将焊接区的机械和结构变化与基础材料进行了比较。观察到工具旋转速度对FSW毛坯的屈服强度和抗拉强度有重大影响，其强度在整个过程和测试的成形参数范围内变化高达20％。与单轴拉伸试验结果相比，使用水力膨胀试验获得的应力-应变曲线使应变值增加了5-10％。在膨胀测试中 在300°C和0.0013 1 / s的应变速率下测试的样品中，仅观察到沿接合线的圆顶顶点处出现断裂区域。在其他FSW参数和工艺组合下测试的样品在该位置没有失败。在拉伸试验中，仅在300°C的成形条件下，在低应变率或高应变率下，使试样在焊接线上断裂。否则，标本会从接缝处脱落。在200℃的温度和0.0013 1 / s的应变速率下获得最大的穹顶高度，作为可成形性的量度。该结果与从单轴拉伸试验获得的应力-应变曲线很好地相关。样品仅在300°C的成形条件下以及在低应变率或高应变率下在焊接线上断裂。否则，标本会从接缝处脱落。在200℃的温度和0.0013 1 / s的应变速率下获得最大的穹顶高度，作为可成形性的量度。该结果与从单轴拉伸试验获得的应力-应变曲线很好地相关。试样仅在300°C的成形条件下以及在低应变率或高应变率下在焊接线上断裂。否则，标本会从接缝处脱落。在200℃的温度和0.0013 1 / s的应变速率下获得最大的穹顶高度，作为可成形性的量度。该结果与从单轴拉伸试验获得的应力-应变曲线很好地相关。