大厚度TC4钛合金窄间隙焊接接头组织性能研究

Effect of Large-Thickness TC4 Titanium Alloy Narrow Gap Weld Structure on Mechanical Properties of Joints

围绕磁控窄间隙TIG焊接(MCNG-TIG)和真空电子束焊接(EBW)大厚度TC4钛合金接头微观结构不均匀性及其对接头力学行为的影响进行了对比研究。利用扫描电子显微镜对两种接头中部焊缝区和热影响区不同区域的微观组织进行了表征,并对接头截面显微硬度分布和室温拉伸性能进行测定。结果表明,两种接头焊缝区皆为网篮组织,但MCNG-TIG焊缝中α板条宽度比EBW焊缝更加细小。热影响区为初生α相+β转变组织构成的混合组织。随着距焊缝中心的距离增大,β转变组织含量降低。MCNG-TIG热影响区中β转变组织比EBW热影响区更加细小。MCNG-TIG接头平均硬度分布为:热影响区>母材>焊缝;EBW接头平均硬度值分布为:焊缝>热影响区>母材。两种接头的室温拉伸强度系数皆达到0.9以上,EBW接头强度和延伸率略高于MCNG-TIG接头。MCNG-TIG接头室拉伸断裂位置位于靠近母材的热影响区,而EBW接头断裂位置位于焊缝中心。拉伸应变演化结果表明,MCNG-TIG接头在拉伸早期阶段在焊缝中和靠近母材的热影响区同时出现了应变峰值区域。随着拉伸的进行,双应变峰值区特征消失,塑性应变主要集中在靠近母材的热影响区。

A comparative study was conducted focusing on the microstructural inhomogeneities and their effect on the mechanical behavior of magnetically controlled narrow gap TIG welding(MCNG-TIG)and vacuum electron beam welding(EBW)of large-thickness TC4 titanium alloy joints.The microstructure of different regions,including the weld zone and heat affected zone,in the middle of the two joints was characterized using scanning electron microscopy.Moreover,the micro-hardness distribution and room temperature tensile properties of the joint sections were measured.The results showed that the weld zone of both joints had a basketweave structure.But theαlath width in the MCNG-TIG weld was finer than that of the EBW weld.The heat-affected zone is a mixture of primaryαphase+β-transformed structure.The content ofβ-transformed structure decreases with increasing distance from weld seam center.β-transformed structure in the MCNG-TIG heat affected zone is finer than that in the EBW heat affected zone.The average hardness distribution of the MCNG-TIG joints is:heat affected zone>base metal>weld seam;the average hardness value distribution of the EBW joints is:weld seam>heat affected zone>base metal.The room temperature tensile strength coefficients of both joints were above 0.9,and the strength and elongation of EBW joints were slightly higher than those of MCNG-TIG joints.The room tensile frac‐ture location of MCNG-TIG joints was located in the heat-affected zone near the base metal,while the fracture location of EBW joints was in the weld seam center.The tensile strain evolution results showed that in the early stage of tensile testing,the MCNG-TIG joints showed both peak strain regions in the weld and in the heat affected zone near the base material.As the tensile proceeds,the double strain peak region feature disappears and the plastic strain is mainly concentrated in the heat-affected zone near the base metal.