The Microstructure and Mechanical Properties of Dual-Spot Laser Welded-Brazed Ti/Al Butt Joints with Different Groove Shapes

Laser welding-brazing was performed to join Ti and Al together. The dual-spot laser beam mode was selected as the heat source in this study. Ti-6Al-4V and 6061-T6 Al alloys were selected as the experimental materials. Al-12Si welding wire was selected as the filler material. The effect of groove shape on the weld appearance, microstructure, temperature field, and mechanical performance of Ti/Al welded-brazed butt joints was investigated. The interfacial intermetallic compound (IMC) layer at the Ti/Weld brazing interface was inhomogeneous in joints with I-shaped and Y-shaped grooves. In Ti/Al joints with V-shaped grooves, the homogeneity of temperature field and IMC layer was improved, and the maximum thickness difference of IMC layer was only 0.20 μm. Nano-sized granular Ti7Al5Si12, Ti5Si3, and Ti(Al,Si)3 constituted the IMCs. The tensile strength of Ti/Al joints with V-shaped grooves was the highest at 187 MPa. The fracture mode transformed from brittle fractures located in the IMC layer to ductile fractures located in the Al base metal, which could be attributed to the improvement of the IMC layer at the brazing interface.

Visual inspection of weld surface quality

Welding is an important method for modern material processing. In actual processing, due to the influence of processing accuracy and welding thermal deformation, various defects often appear in the appearance of the weld. At present, visual inspection is mainly used for the appearance inspection of welds. The detection of weld defects mainly depends on the work experience of the staff. Based on the above background, the purpose of this article is to visually inspect the weld surface quality. This article uses visually obtained fringe images of weld contours as information sources to explore a visual-based weld appearance detection algorithm, including the measurement of weld formation dimensions and the detection of weld appearance defects. This algorithm overcomes manual measurements of the misjudgments and omissions caused by eye fatigue and experience differences. It improves the efficiency and accuracy of welding appearance inspection, and meets the needs of automation and intelligence of the entire welding process. In this paper, a subpixel stripe centerline extraction algorithm based on the combination of the Hessian matrix method and the center of gravity method is used; to further improve the accuracy of the extraction of the centerline of the weld seam, this article also performs the work of removing the wrong points and the compensation of the broken seam. Obtain a fringe centerline with better connectivity. Comparing the extraction algorithms of each centerline, the centerline obtained by this method has high accuracy, less time-consuming and high stability. It laid the foundation for the subsequent inspection of weld appearance. Through the training of the model, the accurate classification and recognition of surface defects of tube and plate welds have been achieved. The experimental results show that the improved vision-based welding surface defect recognition and classification proposed in this paper has better performance and accuracy. Up to 96.34%.

Laser Oscillating Welding of TC31 High-Temperature Titanium Alloy

The joining of high-temperature titanium alloy is attracting much attention in aerospace applications. However, the defects are easily formed during laser welding of titanium alloys, which weakens the joint mechanical properties. In this work, laser oscillating welding was applied to join TC31 high-temperature titanium alloy. The weld appearance, microstructure and mechanical properties of the laser welds were investigated. The results show that sound joints were formed by using laser oscillating welding method, and a large amount of martensite was presented in the welds. High mechanical properties were achieved, which was approaching to (or even equaled) the strength of the base material. The joints exhibited a tensile strength of up to 1200 ± 10 MPa at room temperature and 638 ± 6 MPa at 923 K. Laser oscillating welding is beneficial to the repression of porosity for welding high-temperature titanium alloy.

Microstructure and mechanical properties of cold metal transfer welded galvanized steel/magnesium alloy dissimilar joints

The joining of magnesium alloy to galvanized steel was realized by cold metal transfer method with AZ31 magnesium alloy welding wire. Weld appearance, microstructure and tensile properties of Mg–steel joints under various welding parameters were investigated with different welding heat inputs. The results showed that magnesium alloy-steel brazed joints had good weld appearance. When the welding heat input was 141 J/mm, Zn elements were enriched in the Zn-rich zone (ZRZ), and the interface layer was composed of a large portion of Mg–Zn phases and minor Mg–Al phases. With the increase of welding heat input, Zn elements in the ZRZ gradually decreased, Fe/Al phase appeared in the interface layer, and the strength of welding joint increased. When the welding heat input was 159 J/mm, the tensile strength of welding joint reached the maximum value of 198 MPa. However, when the welding input was increased to 181 J/mm, Zn element in the ZRZ was burnt and volatilized seriously, resulting in poor wetting and spreading properties of liquid phase at the interface zone of the steel.

Investigation of Arc Bubble Affecting the Arc Stability and Improvement of Weld Appearances Using Bubble Constraint Device in Underwater Wet Welding

The generating, floating and collapsing of arc bubble is a special phenomenon in underwater flux-cored wet welding. The configuration changing process of bubble will change the stress on droplet and influence the droplet transfer process. In this study, the shape changing of bubble is captured in graphic and the real-time electric signal data is obtained. The impact of bubble floating and collapsing results in the globular repelled transfer mode, which also reduces the arc stability. A self-designed gas-shield cover is used as a bubble constraint device to improve the welding process stability and weld appearances by limiting the free floating and expansion of arc bubble. The relationships between the cover diameter and the characteristics of weld appearance are studied.