•A novel method of friction surfacing assisted hybrid friction stir welding was proposed to join dissimilar metals.•The tensile load of Ti/Al joints was improved to 12.2 kN, reached 85.3% of the Al base material.•Tool abrasion was totally avoided by introducing a friction surfaced Al-coating layer.•The bonding was combined contribution of nanoscale-IMCs and mechanical interlocking.A new method of friction surfacing assisted hybrid friction stir welding (FS-HFSW) technique was developed to improve the joint efficiency and avoid the pin abrasion for joining of dissimilar Ti/Al joints. The FSW tool with enlarged head and concave end-face was designed to broaden the lap width and promote material flow. The maximum tensile load reached 12.2 kN, representing 85.3% of the parent Al alloy, with a ductile fracture locating at the heat affected zone of base Al. The excellent bonding of Ti and Al was based on the combined effects of nanoscale TiAl3 IMCs layer and complex mechanical inter-locking.Download high-res image (187KB)Download full-size image

•A novel self-riveting friction stir lap welding technique is developed.•A self-riveting structure forms with plasticized aluminum and imposed pressure.•The self-riveting structure can bear load even tearing of interfacial bonding.•The self-riveting structure is beneficial to prevent total failure of joint.•Enlarged elongation enables joint to function under fluctuating load.A novel self-riveting friction stir lap welding technique was developed by the prefabricated holes to realize sound and effective joining of 6082-T6aluminum alloy to QSTE340TM steel. Partial dynamic recrystallized aluminum flows downwards and fills the prefabricated holes forming self-riveting structure. Metallurgical bonding as diffusion layers formed at the interface of Al/Steel. The joint fracture process contains separation of self-riveting structure and unilateral hole wall, tearing of metallurgical bonding and final failure of self-riveting structure. An average fracture load of 3.21 kN is obtained, which is stronger with high average elongation than that without prefabricated holes. The self-riveting structure is beneficial to prevent total failure of different materials joints with applicative perspectives.

In the present study, pure iron/copper composite metal cladding was deposited onto carbon steel by tungsten inert gas welding. The study focused on interfacial morphological, microstructural, and mechanical analyses of the composite cladding layers. Iron liquid–solid-phase zones were formed at copper/steel and iron interfaces because of the melting of the steel substrate and iron. Iron concentrated in the copper cladding layer was observed to exhibit belt, globule, and dendrite morphologies. The appearance of iron-rich globules indicated the occurrence of liquid phase separation (LPS) prior to solidification, and iron-rich dendrites crystallized without the occurrence of LPS. The maximum microhardness of the iron/steel interface was lower than that of the copper/steel interface because of the diffusion of elemental carbon. All samples fractured in the cladding layers. Because of a relatively lower strength of the copper layer, a short plateau region appeared when shear movement was from copper to iron.

•The Al2O3–M7C3/Fe MMC coatings were successfully fabricated by laser cladding.•Thermite reactants addition can enhance the wear resistance of the composite coating.•The excellent wear resistance is mainly due to the presence of hard reinforcements.In the present work, Al2O3–M7C3 particle reinforced iron matrix composite coatings were fabricated on a steel substrate by laser cladding with different mixtures of Fe-based alloy powder and Al/Fe2O3 thermite reactants. The microstructure of the composite coating was investigated by X-ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. The hardness and dry sliding wear properties of the composite coatings were also investigated by Vickers microhardness and block-on-ring dry sliding wear test. The results show that Al2O3 ceramic and M7C3 carbide are in situ synthesized by laser cladding. With the increase of thermite reactants, the amount of Al2O3 ceramic and M7C3 carbide in the composite coatings increases gradually. The microstructure is characterized by a cellular dendritic structure at the bottom, a typical cellular microstructure in the middle and an equiaxed crystal at the top of the composite coatings. The increased thermite reactants significantly enhance the microhardness and the wear resistance of the composite coatings, which should be ascribed to the grain refinement strengthening, precipitation hardening and solid solution strengthening.

•A novel method of self-support friction stir welding (SSFSW) was introduced.•The grain structure and second phase particles of SSFSW joint was reported.•The microstructural development was a strong function of the local thermo-mechanical cycle.•The TMAZ was characterized by coarse equiaxed grains and dissolution of precipitates.In this paper, 5-mm-thick 6082-T6 aluminum alloy was joined by means of self-support friction stir welding (SSFSW). Here we report the grain structure and second phase particles in various regions including the welding nugget zone (WNZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ). In the upper part of the joint, microhardness in the TMAZ in proximity of the UWNZ was the highest (average 89.4 HV) due to the severe plastic deformation. The similar result was also found in the lower part of the SSFSW joint. The microstructural development in each region was a strong function of the local thermo-mechanical cycle experienced during welding. Some coarse equiaxed grains which were produced in incomplete dynamic recrystallization process and dissolution of some precipitates have been observed in TMAZ. The HAZ retained the same grain structure as the base material, however, the grain size decreased with increasing distance of the weld centerline.

Inorganic silica/alumina multilayer films with excellent mechanical and anti-atomic-oxygen erosion properties were fabricated on polyimide by the hybrid implanting and depositing processes. X-ray photoelectron spectroscopy demonstrated that the silica/alumina graded structures consisted of SiO and AlO bonds, as well as AlOSi and AlOC bonds in the transition layers. The results revealed that bonding between the alumina coating and the polymer occurred primarily via AlOC bonds, and SiOAl bonds were formed in the interface between silica and alumina coatings. The multilayer films presented good adhesion property, demonstrating that balanced internal stresses and alternating bonding structures were crucial for enhancing anti-crack performance. The multilayer inorganic films exhibited good anti-atomic-oxygen erosion properties were well matched with the behavior of adhesion property.Highlights► Inorganic multilayer films were fabricated for protection against AO in LEO. ► The graded structures consisted of AlOSi and AlOC bonds in transition layer. ► Multilayer films were stitched by AlOC and SiOAl interconnected bonding networks. ► Balanced internal stress and alternating bonding structure were crucial for stability.

TIG welding–brazing of Ti–6Al–4V to Al5A06 alloys with pure Al and Al–Cu–Zr fillers was investigated. The Zr and Cu additions enhanced the spreadability of Al-based fillers on Ti–6Al–4V substrate under TIG heating condition, and a sound Ti/Al dissimilar butt joint was obtained. Influenced by Zr addition, a discontinuous TiAl3 layer with a thickness of 2–4 μm was observed at the Ti/seam interface under a low heat input condition, which was replaced by TiAl3+L–(Ti,Zr)Al3+H–(Ti,Zr)Al3 multi-sublayers when a high heat input was adopted. The joint with Al–Cu–Zr filler has higher tensile property and wider processing parameters than that with pure Al filler. The largest tensile strength of the joint produced by Al–Cu–Zr filler reaches 284 MPa up to 85% of base Al5A06 alloys, and the fracture occurred by quasi-cleavage mode at the TiAl3 sublayer. Zr addition was favorable to enhance the spreadability on Ti substrate, and the welding processing parameters were broadened by the presence of Zr addition.

Fluxless soldering with surface abrasion has been developed for joining aluminum foams. To improve the wettability of the molten filler metal on the joined surfaces, 2 methods of abrasion were used to remove the oxide film from the aluminum foams prior to soldering. The effectiveness of the abrasion was determined by microstructure observation. The mechanical properties of the joints were examined by tension and compression tests. Assisting with the mechanical abrasion, fluxless soldering using a Zn-based alloy was proven suitable for joining aluminum foams. The joints showed no visible macroscopic deformation and did not cause the foam structure to collapse, which indicates a good wetting process. The mechanical properties of the joints were similar to the parent material, and a higher compressive strength was achieved. Fluxless soldering with surface abrasion not only offers an alternative means to join aluminum foams but also lays the foundation for joining metal foams by soldering.Highlights► A method of fluxless soldering with surface abrasion was introduced to join aluminum foams. ► The metallurgical joint of aluminum foams was achieved, and interdiffusion occurred. ► Surface abrasion was suitable for wetting process.