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Study on Microstructure and Fatigue Propeties of High Density Beams Welded Joints of TC4 Titanium Alloy

Author: ChenBin
Tutor: YangXinZuo
School: Tianjin University
Course: Materials Processing Engineering
Keywords: TC4 titanium alloy High-energy beam welding Lap with stack welding head Fatigue fracture Fatigue strength
CLC: TG407
Type: Master's thesis
Year: 2010
Downloads: 240
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Abstract


The detailed study of the fatigue fracture behavior of TC4 titanium alloy, high-energy beam (laser welding LBW and electron beam welding EBW) overlap stack welding head. First application of ANSYS software, the stress of welded joints centralized computational analysis; Second microstructure of welded joints, micro-hardness, fatigue strength and life characteristics were studied, and the observation and analysis of weld defects on fatigue fracture explore the fatigue behavior of weld defects observed on the fatigue fracture using scanning electron microscopy (SEM); last welded joint fatigue crack initiation and propagation behavior analysis discussion on the law of the mutual influence of the welding defects and fatigue strength. The finite element analysis shows that the type of welded joint and overlapping gap is a key factor of stress concentration, lap joint stress concentration from 6.8 to 7.3 was significantly higher than wide welding head of 1.4 to 2.3, but the lap joint gap increases corresponding force concentrated impact; Laser stacked maximum stress of welded joints the board undercut defects in the weld; electron beam welding bite maximum stress in the upper plate side or the lower plate convex height. The fatigue test results of TC4 titanium alloy lap joint fatigue fracture location of high-energy beam welding in the heat-affected zone. Derived by linear fitting of the fatigue life analysis: laser welding corresponding to N = 2 × 106 fatigue life of lap fatigue strength of 41.3MPa, while the corresponding electron beam welded joints fatigue strength of 39.7MPa; laser stitch welding corresponding to the fatigue strength of welded joints was 210.3MPa, and the fatigue strength of the corresponding electron beam welded joints 184.1MPa laser welded joint has a higher fatigue strength. For lap joints, the main factors affecting its fatigue strength lap gap; stack for laser welded joint, with the undercuts the high increase in the depth and the root of the weld projection, fatigue strength declining; on the surface of the electron beam welding. melting, making its fatigue strength increased by 80% on average. Analysis of fatigue fracture, stress levels and joint form of TC4 titanium alloy welded joint fatigue fracture characteristics. With the increase in the stress level, the increased the smooth small number of facets of the source area and expansion area of ??the fracture fatigue cracking of the initial stage of crack propagation lamellar secondary cracks more obvious expansion area becomes rough, height difference increases; ride joints there are multiple crack source, the speed of crack propagation, basic secondary cracks. The microstructure analysis indicates that the base material of the original TC4 small α β equiaxed grain structure after welding into α β α 'martensite cross mixed uneven and roughened organizational structure. Laser weld basket-like α 'martensite than electron beam remelting the weld heat-affected zone, the situation was exactly the opposite. Laser welding the upper plate and lower plate of the weld and heat affected zone hardness higher than the base material, while the hardness values ??and the base material of the plate by electron beam welding of the weld zone is fairly lower plate of the weld and heat affected zone hardness higher than the base metal. The findings provide an important reference for laser and electron beam welding in the field of aviation manufacturing.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding general issues > Mechanical properties of welded joints and Intensity
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