To improve the weldability of 6061 aluminum alloy and improve the mechanical properties of welded joints, ultrasonic was introduced into the welding process. The microstructure changes of welded joints under different ultrasonic power were studied, and their effects on the mechanical properties of welded joints were analyzed. The grain size was calculated, and the distribution of precipitated phases was observed by the EBSD technique. The results show that the cavitation and acoustic flow produced by ultrasonic vibration can refine the microstructure of welded joint, reduce the grain size by nearly 50%. It promotes the transition of alloy elements to weld and eliminates the segregation of the strengthening phase to the grain boundary, thus improving the mechanical properties of the welded joint.

Q960 high-strength steel is widely used in pressure vessels, bridges, offshore platforms and other important steel structural components because of its high strength and good plastic toughness, but alloy elements added to this kind of steel have strong hardenability, especially after welding, so the strength and toughness cannot meet the requirements, which limits its application in a wider range. In this paper, from the point of view of the metallurgical treatment of the weld, the goal is to improve the strength and toughness of the Q960 high strength steel weld metal In order to analyze the influence of Zr on the welding process of Q960 steel and the strengthening and toughening effect of weld metal, this paper takes Fe-Mn-Mo-Cr-Ni as the main alloy system, BaF₂-CaF₂-Al-Mg as the basic slag system, and adopts the method of melting consumable electrode self-shielded for welding, and analyzes the welding process, microstructure, tensile property and impact toughness of the welded joint. The experimental results show that when the weld metal contains 0.0061% Zr, the minimum spatter rate is only 7%, the maximum slag removal rate is 95%, the maximum hardness is 357HV, the maximum elongation is 34%, and the impact toughness is the highest. At this time, the acicular ferrite content in the weld microstructure is the highest, and there is a certain amount of equiaxed fine-grained ferrite, and the content of proeutectoid ferrite is the least, which effectively improves the strength and toughness of the weld metal.

High-strength low-alloy (HSLA) steel is used in important steel structural members because of its strength and plastic toughness. Q960 steel is HSLA steel obtained by adding an appropriate amount of alloy elements and quenching and tempering treatment on the basis of ordinary low-carbon steel. This kind of steel has strong hardenability due to the alloy elements added. Cold cracks, embrittlement and softening of the heat-affected zone easily occur after welding. In particular, the low-temperature impact toughness cannot meet the requirements and limits its use. In this paper, self-shielded welding is used to adjust the content of aluminum in flux-cored wire. The relationship between weld metal (WM) microstructure and strength and properties was studied by tensile test and impact test, and the influence mechanism of Al content on weld metal microstructure and properties was analyzed. The results show that when the content of Al is 0.21%, the impact energy at 0 °C~−60 °C is the best, the tensile strength can reach 1035 MPA and the number of pores is small. The size of inclusions in WM is mostly less than 1.0 μm Al₂O₃ spherical oxide. It can become the center of acicular ferrite (AF) and increase the nucleation probability. However, with the increase of Al content, large irregular AlN inclusions are produced, which reduces the tensile strength and impact energy of the welded joint.

In this study, a WC-reinforced Ni-based surfacing layer was prepared on Q235 steel plate by plasma arc welding. The effects of nano-Y₂O₃ with different contents (0 wt.%, 0.4 wt.%, 0.8 wt.%, 1.2 wt.%, and 1.6 wt.%) on the microstructure, phase composition, microhardness, and wear resistance of the surfacing layer were studied by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), microhardness test, and pin-on-disk test. The results show that the phase composition of the surfacing layer was γ-Ni, FeNi₃ solid solution, WC, W₂C, M₂₃C6, M₆C, Cr₇C₃, and other carbides. When the addition of nano-Y₂O₃ was 1.2 wt.%, it has a good improvement on microstructure grain refinement and carbide hard-phase increase. Compared with other contents, 1.2 wt.% nano-Y₂O₃ surfacing layer has the highest microhardness and the lowest friction coefficient and wear loss. At this time, the wear mechanism is abrasive wear accompanied by slight adhesive wear.