Effect of bonding temperature and heat treatment on microstructure and mechanical property of Mg−6Gd−3Y alloy vacuum diffusion bonded joints

Diffusion bonding of as-cast Mg−6Gd−3Y magnesium alloy was carried out at temperatures of 400−480℃ with bonding pressure of 6 MPa for 90 min.Diffusion bonded joints were solution treated at 495℃ for 14 h and then aged at 200℃ for 30 h.Microstructures and mechanical properties of joints were analyzed.The results showed that rare earth elements and their compounds gathering at bonding interface hindered the grain boundary migration crossing bonding interface.Tensile strength of as-bonded and as-solution treated joints increased firstly and then decreased with the bonding temperature increasing due to the combined effects of grain coarsening and solid-solution strengthening.As-bonded and solution-treated joints fractured at matrix except the joint bonded at 400℃,while aged joints fractured at bonding interface.The highest ultimate tensile strength of 279 MPa with elongation of 2.8%was found in joint bonded at 440℃ with solution treatment followed by aging treatment.

Effect of joining temperature on microstructure and properties of diffusion bonded Mg/Al joints

The joining of AZ31B Mg alloy to 6061 Al alloy was investigated at different joining temperatures by vacuum diffusion bonding method. The microstructures of Mg/Al dissimilar joints were studied by means of optical microscopy （OM）, scanning electron microscopy （SEM） and energy dispersive X-ray （EDX）. The results show that the thickness of each layer in the diffusion zone increases with the increase of joining temperature, and the microstructure changes obviously. At joining temperature of 440 °C, the diffusion zone is composed of Mg2Al3 layer and Mg17Al12 layer. At joining temperatures of 460 and 480 °C, the diffusion zone is composed of Mg2Al3 layer, Mg17Al12 layer, eutectic layer of Mg17Al12 and Mg-based solid solution. The width of high-hardness zone in the joint increases with increasing joining temperature, and the micro-hardnesses at different locations in the diffusion zone are significantly different. The joining temperature of 440 °C offers the highest tensile strength of 37 MPa, and the corresponding joint exhibits brittle fracture at the intermetallic compound layer of Mg17Al12.

Diffusion welding of SiCp/2014Al composites using Ni as interlayer

SiCp/2014Al composites were bonded with the vacuum diffusion welding technique using Ni as the interlayer metal. Ni and Al were interdiffused and there were intermetallic compounds formed in the inter transition layer, which was composed of Ni3Al//NiAl//NiAl3. The relation between the diffusion distance and the element concentration was calculated according to Fick＇s second law. The relations of the diffusion concentration and the diffusion welding technique parameters were calculated.

Interfacial Microstructure and Properties of Ti(C, N)/Ni Bonded by Transient Liquid-phase Diffusion

Effects of the main process parameters（temperature and time） on microstructure and properties of Ti（C, N）/Ni interface bonded by （Cu＋Nb） interlayer in a vacuum diffusion bonding device were investigated. The interfacial microstructures consisted initially of Ni3Nb metallic compound and eutectic of Ni3Nb ＋ CuNiss, and finally transformed to （Ti, Nb） （C, N）＋Ni3Nb near Ti （C, N） and NiCuss ＋ Ni3Nb near Ni when diffusion bonding temperature was 1 523-1 573 K. It was clear that Cu was a constituent in the transient liquid phase （TLP） into which Ni was dissolved by forming Cu-Ni transition liquid. Nb was dissolved in Cu-Ni transition liquid rapidly. Ti （C, N） conld be wetted by resultant Ni-Nb-Cu transient liquid phase which was followed by a little （Ti, Nb） （C, N） solid solution formed at interface. This increased the interface combining capability. Ultimately the interface shear strength was able to reach 140 MPa. The theoretle analysis and experimental results show that the growth of interfacial reaction layer Ni3Nb accords with parabola law, and the activation energy of diffusion reaction is 115.0±0.5 kJ/mol, while the diffusion reaction speed constant is 12.53 mm/s^1/2.

Microstructure and properties of alloying coating on AZ31B magnesium alloy

Vacuum thermal diffusion technique was applied to preparing alloying coating on AZ31 B magnesium alloy. The microstructure and phase composition of the coatings prepared at different holding time were investigated in detail using optical microscopy（OM）, scanning electron microscopy（SEM）, energy dispersive spectrometer（EDS） and X-ray diffraction（XRD）, and so on. The microhardness tester and electrochemical workstation（PS-168a） were used to measure the microhardness and corrosion resistance of the alloying coating. The results showed that the alloying coatings gradually generated with the extension of holding time under constant temperature. And the obvious bonding interface between the coating and substrate was observed, and the bonding interface was changed from smooth to zigzag. EDS and XRD analyses showed that the microstructure of alloying coating mainly consisted of eutectic α-Mg phase and continuous network β-Al（12）Mg（17） phase. The average microhardness of the coatings increased by 113% in comparison to the substrate, and the self-corrosion potential increased from-1.389 to-1.268 V at the same time.