Wettability, microstructure and properties of 6061 aluminum alloy/304 stainless steel butt joint achieved by laser-metal inert-gas hybrid welding-brazing

Laser-metal inert-gas(MIG)hybrid welding-brazing was applied to the butt joint of 6061-T6 aluminum alloy and 304 stainless steel.The microstructure and mechanical properties of the joint were studied.An excellent joint-section shape was achieved from good wettability on both sides of the stainless steel.Scanning electron microscopy,energy-dispersive spectroscopy and X-ray diffractometry indicated an intermetallic compound(IMC)layer at the 6061-T6/304 interface.The IMC thickness was controlled to be^2μm,which was attributed to the advantage of the laser-MIG hybrid method.Fe3Al dominated in the IMC layer at the interface between the stainless steel and the back reinforcement.The IMC layer in the remaining regions consisted mainly of Fe4Al13.A thinner IMC layer and better wettability on both sides of the stainless steel were obtained,because of the optimized energy distribution from a combination of a laser beam with a MIG arc.The average tensile strength of the joint with reinforcement using laser-MIG hybrid process was improved to be 174 MPa(60%of the 6061-T6 tensile strength),which was significantly higher than that of the joint by traditional MIG process.

MODEL OF LASER-TIG HYBRID WELDING HEAT SOURCE

The welding mechanism of laser-TIG hybrid welding process is analyzed. Withthe variation of arc current, the welding process is divided into two patterns: deep-penetrationwelding and heat conductive welding. The heat flow model of hybrid welding is presented. As todeep-penetration welding, the heat source includes a surface heat flux and a volume heat flux. Theheat source of heat conductive welding is composed of two Gaussian distribute surface heat sources.With this heat source model, a temperature field is calculated. The finite element code MARC isemployed for this purpose. The calculation results show a good agreement with the experimental data.

Numerical Analysis of Energy Effect in Laser-TIG Hybrid Welding

The hybrid source that combined CO2 laser with TIG arc to proceed welding was analyzed. Based on an energymodel, the temperature field and weld shape were calculated numerically. The heat transfer characteristic of thehybrid heat source to workpiece and its effect to weld shape were also analyzed. Through analyzing the enhancementeffect of the hybrid heat source, the absorption effect and defocusing effect of the hybrid arc to laser were calculated,and the regularity of the energy density to the current was obtained subsequently. At last, the critical energy matchesto induce the enhancement effect of CO2 laser-TIG arc hybrid welding were obtained.

Welding characteristics in different laser-TIG hybrid manners

An experiment for determining the laser-TIG hybrid welding characteristics was carried out in three kinds of hybrid methods: CO_2 laser-TIG coaxial hybrid, CO_2 laser-TIG paraxial hybrid and Nd: YAG laser-TIG paraxial hybrid. The experimental results indicate that hybrid welding has two welding mechanisms in CO_2 laser-TIG hybrid welding: deep penetration welding and heat conduction welding. As the effect of the laser-induced keyhole, the arc root is condensed, the current density and penetration depth increase significantly, the welding characteristic is apt to deep penetration welding. When current increases to some degree, the keyhole induced by laser disappears, which produces a shallow penetration and wide bead. The weld exhibits heat conduction welding characteristics. Furthermore, the arc images and weld bead cross-sections of three kinds of hybrid manners were also compared and analyzed at different welding currents, which established the foundation for understanding the welding characteristics of laser-TIG hybrid welding comprehensively.

Novel hybrid method: pulse CO_2 laser-TIG hybrid welding by coordinated control

In continuous wave CO2 laser-TlG hybrid welding process, the laser energy is not fully utilized because of the absorption and defocusing by plasma in the arc space. Therefore, the optimal welding result can only be achieved in a limited energy range. In order to improve the welding performance further, a novel hybrid welding method--pulse CO2 laser-TIG arc hybrid welding by coordinated control is proposed and investigated. The experimental results indicate that, compared with continuous wave CO2 laser-TIG hybrid welding, the absorption and defocusing of laser energy by plasma are decreased further, and at the same time, the availability ratio of laser and arc energy can be increased when a coordinated frequency is controlled. As a result, the weld appearance is also improved as well as the weld depth is deepened. Furthermore, the effect of frequency and phase of pulse laser and TIG arc on the arc images and welding characteristics is also studied. However, the novel hybrid method has great potentials in the application of industrials from views of techniques and economy.

Research on weldability of ZL101/TiB2 MMCs by laser-TIG hybrid welding

The weldability of in situ TiB2 reinforced ZL101 metal matrix composites （ MMCs） was examined using laser-TIG hybrid welding technology. High speed camera was employed to observe the coupled results between laser plume and electric arc. Optical microscope （OM） , scanning electron microscope （SEM） , tensile machine and wearing equipment were used to evaluate the quality of welding joint. The effective hybrid welding was realized and defect-free seam was obtained when the laser power （8 kW）, TIG current （ 100 A） and welding speed （3 nv/min ） were combined. TiB2 distribution became much more homogeneous than the pre-welded, and microstructure of seam was .finer obviously. Tensile and wear resistance test showed that the weld seam presented higher strength and better wear-reslstance properties than the base metal. The results indicated that TiB2 reinforced aluminum matrix composites were successfully welded using the laser-T1G hybrid welding method.

Microstructure and mechanical performance of AZ31/6061 lap joints welded by laser-TIG hybrid welding with Zn-Al alloy filler metal

A series of Zn-xAl(x=0-35 wt.%)alloy filler metals were designed to join AZ31 Mg alloy to 6061 Al alloy by laser-TIG hybrid welding.The effect of Al content on the wettability of filler metals,microstructure evolution and strength of joint was investigated.The results indicated that the strength of joints was improved with the increase of Al content in filler metals.When Zn-15Al filler was used,the ultimate fracture load reached the maximum of 1475.3 N/cm,which was increased by 28%than that with pure Zn filler.The reason is that the Al element acts as a"reaction depressant"in filler metal,which contributes to inhibiting the dissolution of Mg base metal and the Mg-Zn reaction.The addition of appropriate quantity of Al element promoted the precipitation of Al-rich solid solution instead of Zn solid solution.The MgZn_(2) IMCs have lower lattice mismatch with Al solid solution than Zn solid solution,thus the strength of joints is improved.However,the excessive addition of Al caused the formation of brittle Mg32(Al,Zn)49 ternary compounds,leading to the deterioration of joint performance.

Joining mechanism of Mg alloy/steel butt joints with Cu-Zn interlayer by hybrid laser-TIG welding source

Hybrid laser-TIG （tungsten inert gas） welding technology was used to join the Mg to steel with Cu-Zn interlayer. The effect of Al content in Mg alloy on the interface bonding of AZ31BMg/Q235 steel dissimilar butt joints was investigated. For comparison, ZK60 Mg alloy with no Al addition and AZ31 Mg alloy were utilized. The results showed that AZ31/Q235 butt joints with Cu-Zn interlayer, of which the fractures occurred in the Mg weld seam, showed quite sound and reliable interface bonding. The obvious concentration of element Al occurred along the Mg/steel interface. The results indicated that the addition of Cu-Zn interlayer, especially Zn, could significantly decrease the reaction temperature of Fe-Al at the Mg/ steel interface and promote the formation of reaction layer along the interface. The diffusion of Al element on the Mg-Fe interface was increased by the Cu-Zn interlayer. For ZK60 Mg alloy, Mg and Zn approaching the Mg-Fe interface were evaporated. The intense vaporizing could inhibit the direct contact between steel and Mg weld pool, even destroying the possible formation of reaction layer. The intimate interface bonding of AZ31/Q235 butt joints was attributed to the synergistic effect of element AI and Cu.