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Laser welding/brazing of AA5182 Al to ZEK100 Mg in a lap joint configuration was performed by using a Ni interlayer. The stick-out width of Ni interlayer (WNi) had significant effects on the weld appearance, interfacial microstructure and joint strength of laser Al/Mg joints. Weld defects including porosity and crack were largely reduced with the increase of WNi from 2 to 6 mm, but a fracture occurred at the Mg/Ni interface when it increased to 8 mm which led to an immediate failure after welding. Mg–Al, Mg–Ni and minor Al-Ni IMCs were observed at the Mg/Ni interfacial region. The joint strength first increased and then decreased with the rising WNi, which was mainly determined by the width of Mg-Ni IMCs. [ABSTRACT FROM AUTHOR]

The experiment was conducted on the 907A high strength steel T-joint weldment with double pass laser based on the fiber laser welding system. The welds were fully characterized by means of metallography, microhardness and tensile test. It can be concluded that when the welding speed and defocus amount remain unchanged, the width and penetration of two weld beads increase with the increase of laser power. Uniform thin lathy martensite was found in the weld seam, which may have something to do with the preheating by the first scan and the effect of heat treatment of the second pass laser. Residual austenite and a small amount of carbides were found in the heat affected zone (HAZ). The microhardness of weld seam and HAZ are all higher than the base metal. Dimple and cleavage steps feature were easy to be found from the fractograph of the tensile samples, which can be concluded that ductile-brittle compound fracture was reached. [ABSTRACT FROM AUTHOR]

A study of the laser surface hardening process of low carbon steel has been carried out. A tiny lath martensite can be obtained in hardened zone and it can increase the hardness of steel surface. Laser hardening surface treatment can decrease the friction coefficient to improve the wear resistance of steel surface. Softening in overlapping passes by laser-overlapped scanning surface hardening is a difficult problem of laser surface modification. The effect of activation energy of diffusion for carbon atom in steel and heating rate of laser hardening on the decomposition of martensite have been investigated by a diffusion model based on the principle of carbon diffusion in martensite. The results indicated that activation energy for diffusion of carbon in steel plays a main role in hindering decomposition of carbide and increasing heating rate of lap scanning has a limited action in reducing temper softening during laser overlapping scanning. [ABSTRACT FROM AUTHOR]

Galvanised steels have been joined using an arc brazing process with Cu97Si3 as the filler metal. The arcing time ranged from 1 s to 5 s with arcing current of 70 A in flowing argon. Excellent wetting between the base materials and the filler was observed for all samples. The reaction and products were confirmed by analysis of possible reaction products at the interface using thermodynamics, SEM, and EDS methods. From this, the schematic cycle of the interface Fe/Si compound growth mechanisms and fragmentation mechanisms of a whiskerlike intermetallic compound were determined. It has also been observed that Fe5Si3(Cu) particles are most likely to be generated at the interface through 'dissolve separation' 'whiskerlike compound fragmentation', and 'anode spot action' methods in the present arc brazing process. [ABSTRACT FROM AUTHOR]

Galvanised steel sheets have been joined using an arc brazing processing technique with Cu97Si3 as the filler metal. Gas metal arc (GMA) brazing and gas tungsten arc (GTA) brazing tests were conducted in flowing argon and with varying process parameters. Excellent wetting between base material and filler was observed in all samples. Tensile specimens fractured at the base material in samples prepared using optimal brazing parameters. Microhardness tests performed on the cross-sections of joined samples indicated that joint zone hardness is higher than base material or copper filler. Examination using energy dispersive X-ray analysis revealed the presence of intermetallic compound Fe5Si3(Cu) in the joint as well as a small amount of copper inside the base material. The dispersal of fine Fe5Si3(Cu) particles in the joint is the main strengthening factor. The Fe5Si3(Cu) particles were determined to arise from three sorces: whiskerlike fragmentation, dissolve-separation, and anode spot action. MST/6157 [ABSTRACT FROM AUTHOR]

Joining of metal to ceramic is difficult owing to the formation of cracks at the interface of brazed joint. In the present paper, the crack forming metallurgical mechanisms is studied primarily. The vacuum brazing experiments of ceramic Al2O3 and Kovar, Ni, Fe or Co metals are all conducted. It can be obtained that the cracks could be formed at the Al2O3–Kovar and Al2O3–Fe joint, but not at the Al2O3–Ni and Al2O3–Co joint. In addition, the interfacial morphology and compound composition near cracks are confirmed. It can be concluded that the formation of intermetallic compound FexTiy is the main reason why cracks formed. [ABSTRACT FROM AUTHOR]

This work was carried out at temperatures of 1100 - 1140°C for holding times in the range 10 - 90 s. The solution mechanisms of the base metals of the Ti/Fe contact reaction couples and the growth rules of the Ti-Fe compound and β-Ti(Fe) were studied. The results show that the solution process of the base materials is transient, counted by the time in Ti/Fe contact reaction couples. It can be seen that the quantities of the Ti-Fe compound and β-Ti(Fe) can be reduced effectively through controlling the holding time. When temperature is 1100°C and the holding time is less than 10 s, there is no coarse block Ti-Fe compound in the contact reaction liquid phase zone, and the growth process of the lamellar β-Ti(Fe) experiences a latent period. When the holding time reaches 30 s, the density of the lamellar β-Ti(Fe) reaches a maximum value. The thickness of the liquid phase zone reaches 60 μm at a temperature of 1100°C and a holding time of 10 s. [ABSTRACT FROM AUTHOR]