Influence of (Cr₂O₃+Al) powder thermite on nugget in resistance spot welding of 6061 aluminum alloy

The resistance spot welding of 6061 aluminum alloy with addition of Cr₂O₃+Al powder thermite was conducted. With the assistance of reaction heat released by the metallurgical reaction of powder thermite,the quality factors,including the nugget formation,microstructure and mechanical property, were affected by the Cr₂O₃+Al powder thermite during the welding. The experimental results show that the nugget dimensions of 6061 aluminum alloy spot weld was improved effectively as the reaction heat was released. Because the reaction heat lowered the temperature gradient and more heterogeneous nucleation distributed in the central zone of nugget with the addition of Cr₂O₃+Al powder thermite,the large-scale composition supercooling was enlarged in front of the solid-liquid interface upon solidification. This was beneficial to the nucleation of isometric dentrite which was distributed more uniformly. The grain bundles were refined and the cellular crystal region was strengthened, which improved the strength of the spot weld.