| In this paper, the microstructure, the mechanical properties as well as the strengthening and toughening mechanism in joint of TC4 titanium alloys by inertia friction welding were studied. The results show that the rotary speed has a great effect on mechanical properties of joint. Under the conditions of high rotary speed (2140 rpm) and low pressure there are better tensile, impact, and bending properties for as-weld joint, while under the conditions of medium rotary speed(1480 rpm) and lower slip sleep as well as low ratary speed(770 rpm) and large inertia, the tensile properties are better, but the impact and bending properties are worse. The reason is related to the coordination of deformation strengthening at high and low temperature of welded joints as well as the temperature and deformation degree af heat deformation zone (HDZ)in weld. After welding and commercial anealling at 800℃ , the e-longation of joint is significantly improved, but the strength is not decreased, and the fracture toughness is increased too. The microstructure of weld transformed from coarse acicular at the groove to fine equiaxed grain at the centre in the radial direction. The high strength of weld was attributed to fine-grained strengthening, substructure strengthening and cool deformation strengthening. Improvement of elongation of joint is related to weaker cool deformation degree of heat affect zone (HAZ) and uniformity of strength and stress level between weld and base metal. The fracture toughness of weld was poor, which could be explained by the fine grained microstructure , the higher strength level, and the pollution of gas in weld. |
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