Study on welding characteristics of combining laser welding and resistance seam welding joined Ti-6Al-4V lap joints

Combining laser welding and resistance seam welding (LW-RSEW), lap welding of Ti-6Al-4V alloy plates with 1.4mm thickness was carried out and the welding characteristics of LW-RSEW joint were investigated. The results indicate that, compared with “V” profile of LW weld, the cross section of LW-RSEW joint is “cross” profile and the weld width at faying interface is greatly increased, which is correspond to increase the joint shear strength. The LW-RSEW joints fail in the heat affected zone (HAZ) and average tensile shear load is 21.50kN. By means of X-rays inspecting, it’s found that there is almost no porosity in the LW- RSEW joints. The mechanism of porosity elimination was analysed in detail. Furthermore, metallographic examination of the joint reveals that in the nugget the microstructure is coarse β with internally acicular morphology and the HAZ consists of a mixture of primary α and transformed β with some acicular α. Hardness of the HAZ slightly rises compared with base metal (350HV); the hardness in the nugget is highest and the peak value reaches about 425 HV due to the structure transformation to martensite.