[Mechanical properties of weld area soldered by lasers and structural changes in hot reaction zone]

To analyse and measure the welding depths and strengths of three kinds of welding materials under different laser welding conditions as well as the structural changes of the heat affected zone.

Under different voltages and pulse duration three kinds of measuring sticks, including Co-Cr alloy, Ni-Cr alloy and pure titanium were welded and their strengths were compared with that of control group. At the same time, the structure of the heat-affected zone was analysed by means of the gold-phase method.

The welding depth and strength of Co-Cr alloy were in direct proportion to the setting voltage, with averages of 335MPa (250V) to 573MPa(330V). At the heat-affected zone, the crystal particle was small and the end point of welding by laser bean presented the shape of the mountain peak and the interval of finger shape. The center of measuring sticks had a black zone with the circle shape. The setting voltage was in direct proportion to the welding depth of pure titanium and in inverse proportion to the welding strength with averages of 221MPa(250V) to 154MPa (330V). The crystal particle in the heat affected zone grew large and the solid phase expanded, the interval of the crystal oxidised, and the structure showed honeycomb changes.

The laser welding is favourable to the welding properties of Co-Cr and Ni-Cr alloys, but its effect on the welding properties of pure titanium needs further discussion.