T.J. Ma

On microstructure and mechanical properties of linear friction welded dissimilar Ti–6Al–4V and Ti–6·5Al–3·5Mo–1·5Zr–0·3Si joint

Abstract Linear friction welding of dissimilar titanium alloys Ti–6Al–4V (TC4) and Ti–6·5Al–3·5Mo–1·5Zr–0·3Si (TC11) was achieved. Microstructural examination showed that the joint has a clearly identified weld zone and a thermomechanically affected zone on both TC4 and TC11 sides with a clearly identified weld line. In the weld zone of TC4, superfine α grains are dispersed in the β matrix, while in that of TC11, a few recrystallised α grains are observed along the β boundaries. In the thermomechanically affected zone of TC4, both deformed and recrystallised grains exist in the same area, while that of TC11 has a deformed α+β structure. The tensile strength of the joint is comparable to that of the parent TC4 where fracture occurs. The joint microhardness is well related to its microstructure.

Effect of post-weld heat treatment on microstructure and property of linear friction welded Ti17 titanium alloy joint

Abstract In this study, post-weld heat treatment of linear friction welded Ti17 (Ti–5Al–2Sn–2Zr–4Mo–4Cr) titanium alloy joints was performed at 530, 610 and 670°C for 4 h followed by air cooling. Results show that with increasing treatment temperature, the recrystallisation extent of the α and β phases in the weld and deformation zones increases significantly. The overall property of the joint is remarkably improved, and the fracture behaviour of the tensile and impact samples changes from brittle failure to a ductile one. After treatment at 670°C, the impact toughness of the joint is 93·3% of the parent metal, and the failure of the tensile samples occurs in the parent metal far away from the weld. According to these findings, a treatment temperature slightly lower than 670°C but higher than 610°C would be a good value for linear friction welding Ti17 joints.

Microstructure and fatigue properties of linear friction welded TC4 titanium alloy joints

The welded joints are often subjected to cyclic stresses and high-strain-rate deformation resulting in worrisome fatigue failure. Therefore, it is necessary to evaluate the fatigue resistance and cyclic deformation characteristics of these weldments. Ti–6Al–4V–0.3Fe–0.1C–0.05N–0.015H–0.2O (TC4) titanium alloy joints were produced via linear friction welding and a sound joint was obtained. It was observed that fine subgrains formed in the weld zone where the hardness became higher. The strain ratio had a strong effect on the cyclic deformation characteristics of the joint, with hysteresis loops being different at different strain ratios. However, the difference of fatigue life of the joint was small with varying strain ratios. The stress amplitude of linear friction welded TC4 joint showed essentially cyclic softening until failure at all strain ratios. Fatigue cracks initiated from the near-surface of base metal and propagated by the formation of fatigue striations together with secondary cracks.

Experimental Study of Plastic Flow during Linear Friction Welding by Physical Simulation Method

Abstract. In order to study the plastic flow during linear friction welding (LFW), copper particles were added as tracers on the surface of lead block. The flowing state of interior metal in LFW was simulated by the home-made simulator. Results show that the upset speed promotes the plastic flow of metal and the oscillation frequency restrains it. The upset speed influences the plastic flow of metal more significantly than the oscillation frequency. Only when the pressure reaches 800N and the increasing rate reaches 100N/s, can obvious plastic flow of lead happen in the direction perpendicular to the compression. But the plastic flow of lead in the compression direction is visible even if the pressure and its increasing rate are small.

Effects of annealing on microstructure and properties of linear friction welded dissimilar titanium joints

Abstract Linear friction welds of Ti–6Al–4V (TC4, according to Chinese classification) to Ti–6·5Al–3·5Mo–1·5Zr–0·3Si (TC11, according to Chinese classification) were subject to post-weld heat treatment (PWHT) at 650°C×4 h (PWHT1) and at 950°C×1 h+530°C×4 h (PWHT2) under air cooling. In the as welded joint, TC4 had recrystallised sufficiently compared to TC11. After PWHT1, the α grains in the TC4 weld centre zone grew to some extent and many superfine equiaxed recrystallised α grains precipitated along β boundaries on the TC11 side. The grain growth along the weld line in the weld centre zone under PWHT2 was evident. PWHT2 reduced the joint tensile strength due to the coarsening of the microstructure. The joint microhardness decreased after PWHT.

Research on Model of Plastic Flow Heat Transfer during Linear Friction Welding for Low Melting Point Metal

With the self-developed physical simulation equipment of linear friction welding, the plastic flow heat transfer simulation experiment of low melting point Lead metal was implemented. A physical model of plastic flow heat transfer of linear friction welding low melting point metal was established based on the process of the Lead metal plastic flow recorded by high speed digital camera and the Lead metal temperature variation recorded by infrared thermal imager. Introducing the plastic flow element into one-dimensional unsteady heat transfer differential equation, heat transfer mathematical model of plastic zone, perpendicular to the direction of vibration, was proposed. Using finite difference method to solve this mathematical model, calculated value of this model and measured temperature was compared. The results show that the two values correspond basically, which indicates that the proposed model could be used to characterize the process of heat transfer of plastic zone during linear friction welding low melting point metal.

3-Phase 4-Wire VIENNA Rectifier Used in the Resistance Spot Welding Inverter Power Supply

Considering the distortion factor, the large power resistance spot welding (RSW) inverter power supplys actual power factor (PF) is very low. In this paper, the 3-phase 4-wire three-phase/switch/level (VIENNA) rectifier is proposed to realize the power factors correction (PFC). Firstly, an equivalent load model of the back-stage in the RSW inverter power supply is established, thus the real load of this PFC circuit can be archived. Then, the 3-phase 4-wire VIENNA rectifier PFC circuit is analyzed with the simulation software of Pspice. Finally, an experimental circuit power of 3kW is designed. Experimental results show that the PF of this system can be increased to 98.6% that demonstrates the practicability of the 3-phase 4-wire VIENNA rectifier in RSW inverter power supply.

Effect of Process Parameters on Welding Variables during Linear Friction Welding of Ti-6Al-4V Alloy

The orthogonal experimental design was conducted for linear friction welding of Ti-6Al-4V titanium alloy (TC4). The friction power and joint temperature were collected during the welding process. The influence of process parameters on the axial shortening was analyzed. The suitable process parameters were determined by investigating the joint appearance, the requirement of axial shortening and welding variables during welding. The results provide important reference for establishing process parameters of linear friction welding in practice.