MICROSTRUCTURE AND MECHANICAL PROPERTIES EVOLUTIONS OF CONTINUOUS COLUMNAR-GRAINED CuAlNi ALLOY WIRES DURING DIELESS DRAWING PROCESS

Dieless drawing experiments of continuous columnar-grained Cu-14.0%Al-3.8%Ni (mass fraction) alloy wires were carried out at drawing speeds of 0.8-1.1 mm/s and deformation temperatures of 650-900 degrees C, when the feeding speed and distance between the heating and the cooling sources kept invariant at 0.50 mm/s and 15 mm, respectively. Effects of dieless drawing parameters on the microstructure and mechanical properties of the alloy were investigated, and the mechanism of microstructure and mechanical properties evolutions of the deformed alloy was discussed. It was found that the straight continuous columnar-grained boundaries of the alloy wires evolved into regular small zigzag, disordered large zigzag and recrystallized boundaries. When the deformation temperature was 650 degrees C and the drawing speed was 0.8 and 0.9 mm/s, the alloy remained continuous columnar grains with straight boundaries after dieless drawing, while the straight columnar-grained boundaries gradually transformed into zigzag boundaries with the deformation temperature and drawing speed increasing. When the drawing speed was 0.9 mm/s and the deformation temperature up to 850 degrees C. the alloy exhibited obviously incomplete dynamic recrystallized microstructure characteristic, i.e. the original columnar grains were elongated along the deformation direction, and small dynamic recrystallized grains generated at parts of zigzag grain boundaries. The alloy occurred complete dynamic recrystallization at the deformation temperature of 900 degrees C, and the deformed columnar grains were completely replaced by numerous equiaxed dynamic recrystallized grains with larger size. The tensile strengths of the alloy after dieless drawing first showed a very modest increase trend and then decreased greatly, while the elongations kept decrease.