Abstract

In this study, friction stir butt welding was applied to weld an aluminum–zinc alloy produced by semi-solid method (rheocasting). For this aim, the effect of tool rotational and traverse speeds on the microstructure was investigated. The microstructures of the processed materials were studied using optical microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy, and X-ray diffraction. The Vickers hardness test was used to evaluate the hardness of the joints. The results showed that the friction stir welding using optimum parameters improved the structure of the rheocast alloy. The porosities were eliminated due to severe plastic deformation induced to the material, which caused filling the voids. Friction stir welding lead to replacement of the semi-solid structure by finer equiaxed grains, which are formed by continuous dynamic recrystallization mechanism. High rotational speeds and low traverse speeds (high heat inputs) caused formation of larger grains, due to grain growth at higher temperatures. On the other hand, at high heat inputs the eutectic phases were more scattered throughout the microstructure, and super saturated solid solution was formed. Because of this behavior, the relationship between the hardness and grain size of the joints did not follow the classical Hall–Petch equation.

Graphic Abstract

摘要

在这项研究中，摩擦搅拌对接焊用于焊接通过半固态方法（流变铸造）生产的铝锌合金。为此目的，研究了刀具旋转速度和移动速度对显微组织的影响。使用光学显微镜，配备能量色散光谱的扫描电子显微镜和X射线衍射研究了加工材料的微观结构。使用维氏硬度测试来评估接头的硬度。结果表明，采用最佳参数的搅拌摩擦焊可改善流变合金的组织。由于材料引起的严重塑性变形消除了孔隙，从而导致填充了空隙。搅拌摩擦焊接导致更细的等轴晶粒替代了半固态结构，由连续动态再结晶机制形成。由于较高温度下的晶粒生长，高转速和低横向运动速度（高热量输入）导致形成较大的晶粒。另一方面，在高热输入下，共晶相在整个微观结构中散布得多，并形成了超饱和固溶体。由于这种行为，接头的硬度和晶粒尺寸之间的关系不遵循经典的Hall-Petch方程。

图形摘要