Abstract

In the present research, the effects of friction stir welding (FSW) on the microstructure of 7075-T6 aluminum alloy (AA) thin sheet were investigated. For this purpose, three different welding rotational speeds of 600, 1000 and 1600 rpm at the constant traverse speed of 50 mm/min were studied. It was observed that FSW of an AA7075 thin sheet leads to an irrecoverable drastic reduction in the tensile properties. However, it was proven that for a thin sheet, at different rotational speeds, totally very different mechanisms of microstructural evolution were present within the stir zone (SZ). Also, it was observed that the mean grain size and subgrain density of the SZ have a nonlinear relation with rotational speed. Electron backscattered diffraction analysis indicated that continuous and discontinuous dynamic recrystallization is present within SZ simultaneously as the mechanisms of grain refinement, but with different effects. It was confirmed that heat input of the welding process in FSW of a thin sheet has a negligible effect on the microstructure, although the plastic strain is the determinant parameter. Also, the relationship between the microstructural observations and mechanical properties of friction stir-welded AA7075-T6 is discussed.

中文翻译：

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转速对搅拌摩擦焊接7075-T6薄板组织和力学性能的影响

摘要

在本研究中，研究了搅拌摩擦焊（FSW）对7075-T6铝合金（AA）薄板显微组织的影响。为此，研究了在50 mm / min的恒定移动速度下600、1000和1600 rpm的三种不同的焊接转速。观察到，AA7075薄板的FSW导致拉伸性能无法恢复地急剧降低。然而，事实证明，对于薄板，在不同的旋转速度下，搅拌区（SZ）内存在完全不同的微观结构演化机制。另外，观察到SZ的平均晶粒尺寸和亚晶粒密度与转速具有非线性关系。电子背散射衍射分析表明，SZ内同时存在连续和不连续的动态再结晶，这是晶粒细化的机制，但影响不同。可以确定，尽管塑性应变是决定性参数，但薄板FSW中焊接过程的热量输入对微结构的影响可以忽略不计。此外，还讨论了搅拌摩擦焊接AA7075-T6的显微组织观察与力学性能之间的关系。