타이타늄합금의 전자빔용접성

Electron beam weldability of titaniun alloy

&nbsp;&nbsp;Electron beam weldability was investigated for 1 ㎜ thick cold rolled sheets of commercially pure grade titanium and Ti-6Al-4V alloy.<BR>&nbsp;&nbsp;Accelerating voltage of 40㎸, beam current of 6㎃, and weld speed of 0.8m/min was used and focal position of focused electron beam was just on the surface of workpiece.<BR>&nbsp;&nbsp;Microstructure of weld metal, the heat affected zone and base metal was observed using optical microscope. Vickers hardness was measured across the welds and the transverse tensile test was carried out. Hydroformability test was also carried out for the butt welded coupons of commercially pure grade titanium.<BR>&nbsp;&nbsp;For the electron beam welded CㆍP Ti, the average grain size was equiaxed α (15~25㎛) for base metal, coarse equiaxed α (80~200㎛) for weld metal and annealed and enlarged grain(40~120㎛) for the HAZ. The vickers hardness of CㆍP Ti was 180-200Hv for base metal, and 160~180Hv for the weld metal and the HAZ.<BR>&nbsp;&nbsp;For the electron beam welded Ti-6Al-4V alloy, the vickers hardness was 360Hv for the base metal, abd 400~425Hv for the weld metal and the HAZ.<BR>&nbsp;&nbsp;All the failure occurred at the base metal, when the transverse weld tensile test was carried out for both electron beam welded CㆍP Ti and Ti-6Al-4V alloy.<BR>&nbsp;&nbsp;The formability of electron beam welded CㆍP Ti was decreased compared with that of CㆍP Ti base alloy.