Microstructure and Mechanical Properties of Electron Beam Welded Large Thickness Ti-6Al-4V ELI Alloy

The electron beam welding tests of 55 mm thick Ti-6Al-4V ELI titanium alloy plates were carried out by using different defocusing distances and scanning amplitudes, and the weld forming, the microstructure and properties were investigated through metallographic analysis, tensile test at room temperature and microhardness test. The results show that when small defocusing distance is used for welding, increasing the scanning amplitude significantly reduces the depth to width ratio of the weld, and when the defocusing distance is big, undercut defects and obvious spiking defects are easy to appear in the weld bead. The weld microstructure is thick columnar crystals, and the interior of the crystals is composed of acicular martensite α'phase arranged in a cross pattern. When the defocusing distance is -15 mm, the scanning amplitude is 0.2 mm, the tensile strength of the welded joint is higher than that of the base metal, and there is no obvious difference of tensile strength along the depth direction. The mechanical properties of the welded joint are stable. The microhardness of the weld zone is 323 HV, which is 40 HV higher than that of the base metal.