| The hybrid structures of aluminum and stainless steel, which are widely employedin the field of aviation, manufactures of automobiles as well as shipbuilding, attract thegreat attention for its properties of light weight, high strength and corrosion resistance.Joining of aluminum and steel has been a problem that a great many researchers haveracked the brains to solve because of the extremely low solid solubility between themand great difference in thermal properties. Diverse methods have been studied toachieve the effective joints, and the technique of TIG welding-brazing turns out to beone of the most prevailing zones owing to its economical characteristics andconvenience. However the cooperation of filler metal and flux, and the control ofintermetallic compound (IMC) are two essential elements in order to effectuate thejoint of aluminum and steel with high quality.Within this study, the TIG welding-brazing method was employed to join thedissimilar metal (Al/steel) through the agency of precoating technique on the surface ofsteel. The weld wires of Al-Si, Al and Al-Cu were utilized as filler metal separately soas to match them with appropriate special alloying flux. While the base material of fluxwas Nocolok (KAlF465%+K3AlF635%), alloying elements were added to it at somefixed scale. And then the growth of IMC was controlled by a series of metallurgicreactions in the welding conditions, which ensured the excellent mechanical propertiesof joint. The findings indicated that when Al-Si wire was taken as the filler metal, theNi powder in flux would suppress the growth of IMC at interface, which enhanced thestrength of joints, and the strength reached maximum when mass fraction of Ni arrivedat35%in flux. While the pure aluminum wire was taken, the attachment of Al powderin flux would promoted the stable spread of filler metal on steel. Although it didn’thave much influence on the thickness of IMC, Al powder contributed to the increase ofprecipitated phase in seam. The comprehensive properties of the joint with Al wiresreached the maximum when mass fracture arrived at50%in flux. Finally, when itcomes to Al-Cu wires, none elements added to flux could enhanced the properties ofjoint. Moreover the different joints with above3kinds of welding wires were compared, and results showed that the strength of joint corresponding to Al-Cu wireswas the highest, nevertheless its tenacity was extremely poor. For the joint with Al-Siwires, both tensile strength and tenacity were fairly low. And the comprehensiveproperties of joint of pure aluminum were excellent both in strength and tenacity. Sothe conclusion were draw that the Al/Steel joint corresponding to pure aluminum fillermetal matching the Nocolok flux with50%Al powder added possessed the mostsatisfactory mechanical performance.In addition, the pulsed welding technique was employed to effectuate the joiningof aluminum and steel with the thickness of1.5mm,3mm,4mm separately combinedthe above research. The optimal welding process parameters were determined from theview of appearance of weld and the properties of the joints. The relationship betweenmicrostructure and the properties of the joint was given by the observation and analysisof metallurgic graphs of Al/steel joints. For the base metal with1.5mm thickness, onlythe pulsed technique could ensure excellent appearance of seam, while both pulsedwelding and convention method could contribute to brilliant appearance of basemetal’s seam of3mm and4mm thick. However the pulsed welding technique wasobviously able to homogenize the thickness of IMC at interface for base metals of3mm thick, it didn’t show much effects on the base metal of4mm thick.On the basis of above research, with the appropriate fixtures, effective butt jointsof dissimilar metal pipes (Al/steel) were achieved harnessing exact welding-brazingparameters. And the appearance of the seam of pipes was uniform and favorable. |
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