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首页> 外文会议>International Symposium on Friction Stir Welding >Effect of welding parameters on microstructure and mechanical properties of friction stir welded precipitation-hardened aluminum alloys
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Effect of welding parameters on microstructure and mechanical properties of friction stir welded precipitation-hardened aluminum alloys

机译：焊接参数对摩擦搅拌焊接沉淀铝合金微观结构和力学性能的影响

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摘要

Aluminum alloys are widely used in aerospace, automotive, and shipbuilding industries due to their high specific mechanical properties and good corrosion resistance. 2xxx and 7xxx series aerospace aluminum alloys are generally considered as unweldable because of serious hot cracking sensitivity during fusion processes. Friction stir welding (FSW) is a solid-state joining technique, characterized by the plastic flow without melting and solidification problems. So, it is very suited to join various aluminum alloys. Under the combined action of friction heat input and plastic flow, a joint that is unique from conventional fusion welds is produced. Three zones, i.e., the nugget zone (NZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ), are observed on the transverse section. The highest heat input and the most severe plastic deformation occur in the NZ, followed by a decrease in heat input and plastic deformation in the TMAZ, and finally only heat input plays a role in the HAZ. FSW parameters, such as rotation rate, welding speed, plunge depth and tilt angle, and cooling rate, affect the temperature contribution and material flow in various zones, and therefore are responsible for the quality, microstructure and mechanical properties of the joints. Especially, for precipitation-hardened aluminum alloys (2xxx, 6xxx, 7xxx and 8xxx), the HAZ with the coarsening and dissolution of precipitates is the weakest zone that controls the mechanical properties of the FSW joints. In this article, the effect of the rotation rate, welding speed, and tool dimension on the temperature distribution, microstructure, and mechanical properties of the FSW precipitation-hardened aluminum alloys was evaluated. It was indicated that the FSW heat input results in the dissolution and coarsening of precipitates in the HAZs, producing low hardness zones (LHZs) on both advancing and retreating sides. All the thermal cycles experienced by the LHZs under various FSW conditions exhibited approximately the same peak temperature, e.g., 360-370°C for 6061Al-T651. However, the duration of the thermal cycle at higher temperature shortened as the welding speed increased, but is independent of the rotation rate and tool dimension. Furthermore, the evolution in temperature profiles in the LHZs was verified by thermal modeling. By constructing the hardness distribution maps, it was revealed that the change in the shoulder and pin diameters and the rotation rate changed the position of the LHZs, but did not affect the hardness values of the LHZs. However, increasing the welding speed not only moved the LHZs towards the weldcenter, but also increased the hardness values of the LHZs. The FSW joints fractured along the LHZs. The tensile strength of the FSW joints increased as the welding speed increased, but was independent of the rotation rate and tool dimension. Based on these results, two strategies for enhancing the mechanical properties of FSW precipitation-hardened aluminum alloys are proposed, i.e., increasing the welding speed and cooling the HAZs to reduce the coarsening and dissolution of the precipitates. The role of cooling in enhancing the tensile strength of the FSW joints has been successfully demonstrated.
机译：由于其高机械性能和良好的耐腐蚀性，铝合金广泛应用于航空航天，汽车和造船行业。 2xxx和7xxx系列航空航天铝合金通常被认为是不合适的，因为融合过程中的严重热裂解灵敏度。摩擦搅拌焊接（FSW）是一种固态连接技术，其特征在于塑料流动而不熔化和凝固问题。因此，非常适合加入各种铝合金。在摩擦热输入和塑料流动的组合作用下，生产了传统熔焊件独特的关节。在横截面上观察到三个区域，即核对区（NZ），热机械受影响区（TMAZ）和热影响区域（HAZ）。热量输入和最严重的塑料变形发生在NZ中，然后在TMAZ中减少热量输入和塑性变形，最后只有热量输入在HAZ中起作用。 FSW参数，如旋转速率，焊接速度，暴力深度和倾斜角度，以及冷却速率，影响各种区域的温度贡献和材料流动，因此负责关节的质量，微观结构和机械性能。特别是，对于沉淀硬化的铝合金（2xxx，6xxx，7xxx和8xxx），具有粗化和沉淀物溶解的HAZ是控制FSW关节的机械性能的最弱区域。在本文中，评估了旋转速率，焊接速度和刀具尺寸对温度分布，微观结构和机械性能的影响。结果表明，FSW热量导致沉肠中沉淀物的溶解和粗化，在推进和退缩侧产生低硬度区域（LHZ）。在各种FSW条件下，LHZ的所有热循环显示出大致相同的峰值温度，例如660-370℃，6061A-T651。然而，随着焊接速度的增加，较高温度较高的热循环的持续时间缩短，而是与旋转速率和刀具尺寸无关。此外，通过热建模验证了LHz中温度谱的进化。通过构造硬度分布图，揭示了肩部和销直径的变化和旋转速率改变了LHZ的位置，但不影响LHz的硬度值。然而，增加焊接速度不仅将LHZ移动到焊接中心，而且增加了LHz的硬度值。 FSW关节沿LHz裂开。随着焊接速度的增加，FSW接头的拉伸强度增加，但与旋转速率和工具尺寸无关。基于这些结果，提出了两种提高FSW沉淀硬化铝合金的机械性能的策略，即，增加焊接速度并冷却危险以减少沉淀物的粗化和溶解。成功地证明了冷却在增强FSW关节的拉伸强度的作用。

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