Research On The Welding Process Of CNTs/Al Composites

Aluminum matrix composites have been widely applied in the fields ofaerospace, aviation, automobile manufacturing industries, electron and opticsindustries due to its excellent comprehensive properties such as low density, highspecific strength, corrosion resistance and good processability. CNTs reinforcedaluminum matrix composite is one kind of metal matrix composites. At present, it hasbeen focused on the fabricating of this material, however, no reported researches havebeen done in the welding process of it. Thus, in the present paper, the TIG welding,electron beam welding and friction stir welding have been applied to join the CNTsreinforced aluminum matrix composites which fabricated by friction stir processing,and the welding process of CNTs/Al composites were systematic studied in this paper.Mechanical properties of welded joints of CNTs/Al composites were explored, themicrostructure and phase compositions of welded joints of CNTs/Al composites wereobserved by optical microscope, scanning electron microscopy, energy spectrumanalysis and X-ray diffraction, etc. The distribution of CNTs in weld was studied byKelvin probe experiment, the main results were as following:The result on TIG welding for CNTs/Al composites showing that the weld shapewere very poor, however, the weld shape was enhanced when welding in the argonbox full of argon. The TIG welds prone to generating the defects such as porosity andcracks, at the same time, a lot of lath phase Al4C3produced in weld. Themicrohardness was decreasing in weld metal of the joint. According to the result ofKelvin probe test, the CNTs burn out in joints seriously and uneven distributed inweld which decreased the mechanical properties of the joints.The result on TIG welding for CNTs/Al composites showing that, since theenergy density of electron beam welding process is higher than the TIG welding, themassive needles phase Al4C3was generated in the weld, the quantity and size of Al4C3compounds is closely related to the temperature gradient of molten pool. And thequantity and size of Al4C3compounds increased with the increasing of beam currentand the decreasing of welding speed. The CNTs were also burning out and unevendistributed in weld, but the burning out of CNTs was more serious than in TIG weld.The microhardness was significantly decreased in weld metal of CNTs/Al composites electron beam joint, and with the increasing of the welding heat input, the softeningdegree of weld intensified.According to the fusion welding character of CNTs/Al composites, the CNTs/Alcomposites with different volume fraction of CNTs were welded by friction stirwelding, and a good weld shape and excellent properties welding joint was obtained.The CNTs distributed uniformity in weld. And the interfacial reaction occurredbetween the CNTs and matrix which generated Al4C3. The softening phenomenon wasalso occurred in the FSW joints of the composites, the microhardness was decreasing.With the increasing of the contents of CNTs, the strength of the joint was increasing,when the content of CNTs was5%, the joint strength up to95%of the base materialstrength. Tensile specimen fracture analysis shows that the fracture of compositeswere ductile fracture, and the fracture located at weld, the fracture processingdominates by debonding between CNTs and matrix and the pull out of CNTs, theCNTs play a bridging effect. The results show that it is effective to take friction stirwelding technology to enhancing the joint properties of carbon nanotubes reinforcedaluminum matrix composite.