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Inconel718 superalloy samples with V-grooves were experimentally repaired by electromagnetic stirring assisted laser repairing (EMS-LR) under different magnetic field currents. The effects of the magnetic field current on morphologies of single pass repaired zone (RZ), microstructure and mechanical properties of multilayer RZ were experimentally investigated. Microstructure observations show that metallurgical bonding is obtained between the RZ and the substrate when the optimized process parameter is used. The microstructure in RZ is coarse columnar crystal when no electromagnetic stirring is used, which grows epitaxially along the deposition direction. With the increase of magnetic field current, the convection of liquid metals prompts the transformation from coarse columnar to fine equiaxed grains. The strong scour of liquid metal convection can affect the interdendritic γ+Laves eutectic reaction and prohibit the growth of Laves phase. Electromagnetic stirring can improve the spreading of liquid metal in a certain extent. The width and deposition height of the single trace were measured and it is found that the width and deposition height ratio changes from 3.26 when no electromagnetic stirring is used to 3.33, 4.14 and 5.14 when the applied magnetic field current is 20, 40 and 60 A, respectively, and the penetration is found to be decreased inversely. The tensile strengths of repaired components increase from 487 MPa to 510, 673 and 770 MPa for magnetic field currents of 0, 20, 40 and 60 A, respectively.

A double reinforced layer on an aluminum alloy surface was produced using friction stir processing (FSP) by adding 34CrNiMo6 powder into Al (AA2024) substrate for better wear resistance and gradient transitions. The microstructures of the composites were analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The phase composition was examined by X-ray diffraction (XRD). The results show that the double reinforced layer of the Al13Fe4 intermetallic compound could be successfully fabricated via FSP. The volume fraction of Al13Fe4 in the double reinforced layer was higher than in the single reinforced layer due to adding 34CrNiMo6 powder and reinforced twice, and the Al13Fe4 particles were dispersed more homogeneously in the double reinforced layer. The interfaces between the double and single reinforced layer had a good metallurgical bond. The microhardness of the double reinforcement layer was significantly increased. Compared with the AA2024 substrate, the microhardness of the double and single reinforced layers increased five- (576 HV) and two-fold (254 HV), respectively.

Five tools with different pin-tip profiles like thread taper, triangular, square, three grooves, and conical platform were designed to friction stir weld 20-mm-thick AA7075 alloy plates. The effects of pin-tip profiles on thermal cycles, material flow, and mechanical properties of the joints were studied. The results show that the temperature greatly decreases from the top to the bottom of the weld, and higher peak temperatures along the thickness are obtained using three grooves tool. Due to poor plastic flow reflected by local transfer behavior of material, thread taper and conical platform tools yield macro cross-sectional level pore defect on advancing side in nugget zone. However, triangular, square, and three grooves tools produce defect-free joints due to improving plastic flow resulted from stronger pulsating action and stirring power, leading to higher transfer displacements of local material. The tensile test results show that the joints fabricated by three grooves tool have better mechanical properties including strength and ductility owing to better material flow. A higher ultimate tensile strength of 391 ± 10 MPa, yield strength of 310 ± 12 MPa, and elongation of 8.3 % are obtained, respectively. This can be attributed to finer grains, greater natural aging response and optimum hardness.

In this study, 20-mm-thick 7075-T6 aluminum alloy plates were joined by friction stir welding, and the temperature field, microstructure evolution, and mechanical properties of the joint along the thickness were investigated. The temperature profiles in different zones of the weld were measured by designing various thermocouple layouts. Fine dynamic recrystallized structures in the nugget zone (NZ) were observed, and different grain sizes were estimated by electron back scattering diffraction (EBSD) along the thickness. Also, the precipitate distributions and types in different locations were characterized by scanning electron microscope (SEM) and transmission electron microscopy (TEM) techniques. Vickers microhardness was measured across different cross sections of the weld. Moreover, the results of tensile properties showed that the slice in the middle-upper had the highest ultimate tensile, yield strength, and elongation compared to other slices. Most of the failures for the joints presented a ductile fracture. All results were consistent with a temperature gradient along the thickness during friction stir welding (FSW).

In this study, a new solid-state technique of friction stir additive manufacturing (FSAM) based on friction stir welding (FSW) principle was used to build successfully a multilayered stack of an Al-based component. The results show that a hook stretches into the nugget zone on advancing side, while it moves upwards to the periphery on retreating side for a single-level welding. With manufacturing the second layer, the hooks bend outward significantly attributing to the extrusion of above plastic material, which can avoid the hook to stretch into the stirred zone. A transition zone (TZ) is also formed near the interface between two layers. In addition, fine equiaxed grains are observed due to the dynamic recrystallization in the whole. However, a difference in grain size still exists through the build direction and in the TZ is forming coarse band grains. A similar change occurs in the precipitate morphology, size, and distribution. Form the top to the bottom, the microhardness changes dramatically, and a maximum 115 HV at the top is obtained. The tensile strength of all the slices increases and the elongation decreases slightly in comparison of Al substrate, and the slice top has the highest mechanical properties, which is attributed to fine grains and desirable precipitate characterization.

Three kinds of cooling conditions, i.e., water cooling, metal cooling, and air cooling, were used to prepare 34CrNiMo6 steel thin-wall component by laser rapid forming (LRF) technology. The microstructure and mechanical properties of LRFed thin-wall component were investigated. Results indicate that 34CrNiMo6 steel thin-wall components without internal defect could be fabricated under three kinds of cooling conditions. Cooling condition has a significant effect on the microstructure and mechanical properties of LRFed thin-wall component due to the different tempering effects of subsequent LRFed process. The microstructure along the deposited direction is substantially uniform under the water-cooling condition, which consists of bainite and retained austenite. However, the microstructure of gradient structure changes from bainite to ferrite in thin walls produced under the metal-cooling and air-cooling conditions. The LRFed component under the metal-cooling condition has the best tensile property, of which the maximum tensile strength, yield ratio, and elongation reached to 993 MPa, 0.78, and 10.4 %, respectively. The LRFed component under the water-cooling condition is most brittle, and it is only 4 %. In contrast, the LRFed component under the air-cooling condition has the best plasticity.

The effects of the solution treatment temperature on the microstructure, the chemical composition homogeneity and the microhardness of laser solid forming GH4169 superalloy were investigated. It is found that the grain boundaries become clearer with increasing of the solution treatment temperature. The recrystallization occurs when the samples are solution treated at 1000–1170 °C for 1 h; when the solution treatment temperature is higher than 1000 °C, a large number of twin crystals can be observed, and the grains are refined remarkably compared with the as-deposited grains. The chemical homogeneity can be achieved through solution treatment at 1100 °C for 1 h. With increasing of the solution treatment temperature, the microhardness first decreases rapidly, and then slowly when the solution treatment temperature is above 1100 °C. The variation of microhardness can be explained based on the precipitation behaviors of γ′, γ″ and δ phases during the solution treatment. It is concluded that the temperature of 1100 °C is the low limit of solution treatment temperature range for laser solid forming GH4169 superalloy.