| TD3alloy, with a nominal composition of Ti-24Al-15Nb-1Mo, was a kind ofTi3Al-based alloy with moderately high Nb content. It had a lot of good properties such asoxidation resistance, high fracture toughness, excellent plasticity and high-temperaturesoftening resistance. TD3alloy was a promising alloy which can be applied as hightemperature structural materials in the fields of aeronautics and astronautics. Because itcan endure high temperature between700℃and1000℃. Compared with the traditionalweld technology, laser welding had incomparable superiority on various aspects such asthe welding precision, efficiency, automation and so on. In recent years, laser weldingtechnology was applied in automobile industry, energy industry and other fields.In this paper, the influence of welding parameters on microstructure and mechanicalproperties for laser welded TD3alloy joints were studied. Ring rolling TD3alloy andforging TD3alloy were used in the paper. The results were shown as follows:（1）Under the condition of the front side gas protection, weld bears were alloxidated, and horizontal cracks appeared in the welding joints at the same time. When thewelding speed was30mm/s and laser power was changed from2500to2900W, with theincrease of the laser power, the welding process was deep pentration, and weld profilechanged from V-shape to X-shape and then to V-shape. With the increase of the laserpower, the deep-aspect ratio decreased, the deformation of parent metal increased, and thewidth of heat affected zone changed along with the change of weld cross section shape.When the laser power was2000W and welding speed was from15to25mm/s, weldingprocess was heat conduction welding due to the low power density, and the weld bearswere all incomplete penetration.（2）When forging TD3alloy and ring rolling TD3alloy was laser welded, a gasprotection in the bottom and on the side from the welding process was needed. The sidegas flow no matter too large or too small would have a bad influence on the weldingprocess. With the increase of the laser power, the width of heat affected zone increased.When laser power increased to a certain degree, the width of heat affected zone decreased,the width of weld bear increased and the size of columnar grain grew in the welded zoneincreased at the same time. With the increase of the welding speed, the width of heataffected zone decreased and the size of columnar grain decreased in the weld bear zone. （3）The main phases of far weld zone were β phase and primary2phase in thelaser welding of forging TD3alloy. And the main phases of near weld zone were β phaseand some residual primary2phase. The main phases of far weld zone were primary2phase, β phase and some O phase in the laser welding of ring rolling TD3alloy. And themain phases of near weld zone were β phase and minor residual primary2phase.（4）The average microhardness of the heat affected zone and the weld bear washigher than the average microhardness of the parent metal, and the average microhardnessof the heat affected zone was the highest. When the laser power was greater, the averagemicrohardness of the welding joint was higher. When the welding speed was faster. theaverage microhardness of the welding joint was lower. With the increase of the heat input,the average microhardness of the heat affected zone and the weld bear zone was generallyin an increasing trend. The tensile test in the room temperature showed that all joints ofthe forging TD3alloy fractured in the heat affected zone. Most joints of the ring rollingTD3alloy fractured in the heat affected zone and the tensile strength of the joints waslower than the tensile strength of the parent metal. The tensile strength of welding jointwith side gas flow of20L/min was higher than the tensile strength of welding joint withside gas flow of30L/min. For forging TD3alloy, with the increase of the line heat input,the tensile strength increased. But if the heat input was too high, the tensile strengthdecreased. The fracture surface of heat affected zone and weld bear, no matter forgingTD3alloy laser welding joints or ring rolling TD3alloy laser welding joints, presented thecharacteristics of brittle fracture. The fracture surface of parent metal was brittle fracture.But fracture surface exhibited toughening nest like properties, which indicated someplastic of the joint. |
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