In this work, a welding solidification crack sensitivity test platform was established to study the effect of wire feeding speed (WFS) on solidification crack sensitivity during cold metal transfer (CMT) welding for AA6061 aluminum alloy. The test results show that as the WFS increased from 4 m/min to 5.5 m/min, the sensitivity of the solidification cracks also increased. With a further increase in the value of the WFS, the crack sensitivity decreased and eventually ceased to exist. A new perspective of the microstructure and crack propagation mechanics model was applied to understand the effect of WFS on solidification cracks. With the use of scanning electron microscopy (SEM) and a high-speed camera, it was found that as the WFS increased from 4 m/min to 5.5 m/min, the microstructure of the grain size changed from bigger to smaller, and the stability of the crystal microstructure was reduced. The crack propagation mechanics model was changed, which promotes crack propagation, increasing by 233%. When the WFS continued to increase beyond 5.5 m/min, the size of the crystal structure changed from small to big, the stability of the crystal microstructure was increased, the crack generation was suppressed, and the cracking rate was significantly reduced.

Background: Laser additive manufacturing has been used for surface repair and remanufacturing due to fast laser processing speed, high energy density, and dense microstructure. However, the properties of coating samples produced by laser additive manufacturing of iron-based alloys vary considerably, resulting in a large amount of data that needs to be accumulated and analyzed. Methods: The coating properties of iron-based alloy powders manufactured by laser cladding are studied. The optimal process parameters of the laser cladding are determined by exploring and comparing the macroscopic appearance, hardness, and conductivity of the junction of the cladding. Results： From the macroscopic appearance, when the ratio of the height to the width of the cladding layer is 3.615, the surface of the cladding layer has a smooth surface and is closely combined with the substrate. Conclusion： The hardness of the cladding layer is found to increase significantly, with an average hardness of 663 HV. Besides, it is found that the blackhead's hole causes the conductivity change. The ratio of the largest hole area to the smallest hole area is 8.29 times, and the depth ratio is 1.91 times, but the average resistance ratio is about 1.6 times.

DP780 dual-phase galvanized steels with 0.8mm thickness were lap welded by 4kw continuous fiber lasers to investigate the formation of porosity. By observing the welding parameters and recording the welding process with high speed cameras, the formation mechanism of internal porosity and external porosity was proposed. Based on the formation mechanism of porosity, we established the escape channel model of zinc vapor leaving the molten pool during the welding process, by controlling the dynamic balance of the pores of each channel to reduce the welding internal pores and external porosity defects, improve the welding quality.