钛合金厚板T形接头搅拌摩擦焊工艺对组织性能的影响研究

Effect of Friction Stir Welding Process on the Microstructure and Properties of the T-Joint of Titanium Alloy Thick Plate

摘要

本文对10 mm厚的TC4钛合金T形接头进行了搅拌摩擦焊(FSW)工艺试验,设计了钛合金T形接头搅拌摩擦焊工装,分析了筋板凸出高度和搅拌头旋转速度对焊缝成形的影响,并探讨了焊缝组织演变和力学性能的规律. 结果表明,搅拌头的挤压作用会导致T形接头筋板在焊接过程中凹陷,使得焊缝成形困难．当筋板凸出高度为1 mm、轴肩下压量为0.2 mm、旋转速度为150～250 r/min、焊接速度为50 mm/min时,成功制备了10 mm厚无缺陷的钛合金T形接头．钛合金T形接头横截面上焊缝呈现碗状结构,包括母材(BM)、热影响区(HAZ)、热机影响区(TMAZ)和搅拌区(SZ)4个区域．母材包括长条状α相及岛状晶间β相,平均晶粒尺寸为4.65 μm．相较于母材,热影响区呈现片层状α＋β组织和等轴α相混合结构,平均晶粒尺寸为5.17 μm．搅拌区上部、中部和热机影响区则形成了片层状α＋β组织,搅拌区下部热影响区呈现片层状α＋β组织和少量等轴α相混合结构．其中热机影响区晶粒尺寸为3.18 μm,搅拌区上部、中部与下部高温停留时间和散热条件不同时,晶粒尺寸分别为7.40 μm、8.83 μm和6.53 μm,呈现明显的梯度变化．T形接头横截面显微硬度分布呈W形分布,抗拉强度随焊接转速增加而降低．当旋转速度为150 r/min时,T形接头沿壁板方向的抗拉强度达1 022 MPa,沿筋板方向的强度达810 MPa,断裂位置均位于热影响区,壁板断口呈韧性断裂特征,筋板断口呈韧-脆混合断裂模式．

Abstract

This study conducted friction stir welding(FSW) process tests on 10-mm-thick TC4 titanium alloy T-joints. A friction stir welding fixture for titanium alloy T-joints was designed, and the effects of the rib plate protrusion height and the rotational speed of the stirring tool on weld formation were analyzed. The evolution of weld microstructure and the laws of mechanical properties were also investigated. The results indicate that the extrusion effect of the stirring tool causes the rib plate of the T-joint to sink during the welding process, thereby making weld formation challenging. When the rib plate protrusion height is 1 mm, the shoulder plunge depth is 0.2 mm, the rotational speed is 150—250 r/min, and the welding speed is 50 mm/min, a defect-free 10-mm-thick titanium alloy T-joint is successfully fabricated. The cross-section of the titanium alloy T-joint weld exhibits a bowl-shaped structure comprising four distinct regions: the base metal(BM), the heat affected zone(HAZ), the thermomechanically affected zone(TMAZ), and the stir zone(SZ). The base metal consists of an elongated α-phase and an island-like intergranular β-phase, with an average grain size of 4.65 µm. In contrast to the base metal, the HAZ has a mixed structure of lamellar α＋β and equiaxed α-phase, with an average grain size of 5.17 µm. The upper and middle parts of the stir zone, and the TMAZ, form a lamellar α＋β structure, whereas the lower part of the HAZ of the stir zone exhibits a mixed structure of lamellar α＋β and a small amount of equiaxed α-phase. In the TMAZ, the grain size is 3.18 µm. Because of the differences in high-temperature residence time and cooling conditions in the upper, middle, and lower parts of the stir zone, the grain sizes are 7.40 µm, 8.83 µm, and 6.53 µm, respectively, showing a distinct gradient variation. The microhardness distribution across the T-joint cross-section exhibits a W-shaped profile, and the tensile strength decreases with the increase in the welding rotational speed. At a rotational speed of 150 r/min, the tensile strength of the T-joint along the skin plate direction reaches 1 022 MPa, whereas that along the rib plate direction is 810 MPa. The fracture locations are all within HAZ, with the skin plate fracture showing ductile fracture characteristics and the rib plate fracture exhibiting a mixed ductile-brittle fracture mode.

关键词

TC4钛合金 / T形接头 / 搅拌摩擦焊 / 组织演变 / 力学性能

Key words

TC4 titanium alloy / T-joint / friction stir welding(FSW) / microstructural evolution / mechanical property

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基金资助

国家重点研发计划资助项目(2023YFB3710602)

国家优秀青年科学基金资助项目(52322408)

航空基金资助项目(20240011048001)